Download MULTIPLE ALLELES Characteristics of multiple alleles – Skin colour

MULTIPLE ALLELES
Mendel’s concept of inheritance envisaged alternative forms of a gene or a factor .
This would mean that each gene had two alternative forms or allelomorphs (also
called alleles) ,one being dominant or partially dominant & the other recessive,one
being wild form & the other mutant.However soon it became know that a gene can
have more than two allelomorphs making a series of multiple alleles. It is also
possible that several alleles exhibit themselves within the same phenotypic range,
whether wild or mutant. Such alleles expressing themselves within the same
phenotypic range are called as isoalleles. If the phenotype is wild,these are normal or
wild isoalleles & if the phenotype is mutant, they will be called mutant isoalleles.
eg. Multiple alleles for eye colour in drosophila can be represented as red –W;
apricot –wa, eosin we, ivory –wi, blood-wb,cherry-wc etc. In fact, multiple alleles are
the mutant forms of the same gene & transmit the same character with different
phenotypic expression.
Characteristics of multiple alleles –
a) Multiple alleles always occupy the same locus in the homologous
chromosomes.
b) Multiple alleles do not exhibit the process of crossing over in themselves due
to the same loci.
c) Multiple alleles always regulate a particular character.
d) Among the alleles produced, the wild type is almost always dominant over the
normal allele. The other mutant alleles may be either dominant or
intermediate.
e) Multiple alleles on crossing with two of its mutant type produce progeny
which possess the mutant type phenotype & not the wild type.
Skin colour in rodents –
In Rabbits, four kinds of skin colour are known. Rabbits are accordingly
classified as coloured agouti , chinchilla , Himalayan , albino(having pink eyes &
white coat colour except at the ties like nose ,tail & feet etc. which are black) &
albino .These various coat colours are controlled by a series of four alleles & can be
denoted as follows- C, cch,ch,c.
1) wild type / agouti /coloured- The allele “C” is responsible for agouti & it is
dominant to all other alleles. The hair on the body are brownish grey, the
middle part is yellow & the tip of the hair is black.
2) Albino – The allele ‘c‘ is responsible for albino & it is expression to ‘C’ due to
of skin
3) Chinchilla – The allele cch is responsible for the chinchilla & is recessive to ‘C’
allele. The coat colour is lighter than wild grey & without yellow band.
1) Himalayan – The allele ch is responsible for the Himalayan & it is dominant
only over ‘c’ & recessive to ‘C’.The coat colour is white but the extremities of
the body such as ears, nose, lips of limbs & tail or dark brow
GENETICAL EXPLAINATION FOR THE COAT COLOUR &
THEIR INHENITANCE
The normal colour of the coat of the wild type (Agouti) rabbit is brownish grey
which carry the genetic constitution ‘CC’ for brownish grey colour. Sometimes due to
mutation, the chemical composition of one of the ’C’ allele in a developing germ cell
has changed & it acts as a recessive allele. This changed allele is called mutant ‘c’
allele.
Suppose ,when the gamete containing allele ‘c’ in place of allele ‘C’ unites with
the gamete containing usual allele ‘C’ then the resulting individuals obtained in
F1generation are having genetic constitution Cc. These F1 individuals when produce
the gametes, half of them contain ‘C’ allele & half containing ‘c’ allele. In F2
generation when two gametes, each containing ‘c’ unite with each other, produce an
individual having genetic constitution ‘cc’ which is albino.
Like the mutation from ‘C’ to ‘c’, it is happened sometimes that in case of wild
type rabbit having the genetic constitution ‘CC’ the chemical composition of one of
the ‘C’ allele in a developing gem cell becomes changed by mutation.At this time the
resulting allele partially restricts the development of colour & it forms the colour only
in the extremities. Let us denote this changed allele as C h. When in an individual two
such type of alleles ,one coming male parent & other from the female parent, then it is
called Himalayan individual Ch Ch.
Similarly, the mutation from C to Cch takes place & the changed allele Cch
produce the chinchilla colour.
ABO Blood Groups in Humans In 1900 -1901, Karl Landsteiner at the university of Vienna in the process of
trying to learn why blood transfusions sometimes cause deat & at other times save a
patient in humans ,discovered ABO blood groups. For this discovery, thirty years
later, he belatedly received the 1930 Noble Prize in Physiology or Medicine. These
blood groups were established on the basis of presence & absence of certain antigens
‘A’ or ‘B’& as a result four blood groups were established. These blood groups are
now popularly described as ABO blood groups or Landsteiner blood group.
Inheritance of blood group -
MENDELIAN PRINCIPLES
Gregor Mendel ( 1822-1884) was born to a poor family in an area which is now
part of Czeckoslovakia. At very early age he was ordinates a priest of Augustinian
monastery. Later he was sent to University of Vienna & was working as a teacher of
natural science at Brunn. He developed the statistical skill which paid him a lot in his
experimental studies. In his monastery garden, he carried out his famous experiments
on the garden peas from 1857 to 1865. After many years of studying the garden pea,
he was able to put forth in laws of inheritance. These laws were known as Mendelian
theories. The results of his classic experiments & conclusions are basic to the science
of heredity . His work remained unnoticed until his theories were rediscovered 26
years after his death.
MENDELS WORKMendel took garden pea-Pisum sativum, as his experimental material due to
certain helpful & suitable reason.
a) pollination in this plants could be easily controlled, hence cross pollination
was easy.
b) Pea plants were easy to cultivate .
c) Pea plants had many sharply distinct inheritable different (Mendel had chosen
only seven diff. characters)
d) Large number of offsprings were obtained there minimizing the error.
MONOHYBRID CROSS –
Mendel considered only a single trait i.e. height of the pea plant. He selected &
crossed a tall variety with a dwarf variety. He then considered tall variety as a male
parent & dwarf variety as a female parent. (P1). The resole seeds obtained were tall
plants. The progeny of hybrid obtained were called first filial or F1 generation.
Again he made reciprocal cross by consider tall variety as a female parent &
dwarf variety as a male parent. Reciprocal cross also gave the same results as above.
He then allowed F1 hybrids to self pollinate to find out what had happened regarding
dwarfness. After self fertilization (i.e. F1*F1) the mixed progeny obtained were called
second filial generation or F2. In F2 generation 1064 plants were obtained & out of
these 787 were tall and 277 were dwarf. Is 3:1 ratio (monohybrid ratio). In other
words 75% tall & 25% dwarf. Hence the phenotypic ratio is 3:l & generation ratiois
1:2:1 i.e.25%pure tall ;50% hybrid tall ;1pure dwarf in F2 . Subsequently the ratio
obtained in F3 generation is 3:l & so on.
Depending upon the result obtained Mendel came to certain conclusion & put
forth Mendel’s principles. These are as follows –
1) Principle of unit characters – Mendel said that there was something in
the plant germ cell which controlled the transmission of certain characters.
In his experiments on inheritance of the trait height found that in F1
generation all plants were tall. In F2 generation tall & dwarf plants were produced.
He then conluded that tallness & dwarfness is controlled by something which is
transmitted from parents to offsprings through the gametes.
To this something Mendel coined the term “factors” or “unit”. These
factors were present in sex cells (pollen & egg or sperm or ova). They from the
connecting bridge betn parents & their offsprings. These ‘factors’ occurs in a
pair.Each parent passes only one factor of a pair to the F1 offsprings. Based on this
, Mendel put forth “law of unit characters” ,which states that every trait is
controlled by a factor occur in a pair. The factors in a pair are always contrasting.
These tallness is factors are called alleles or allelomorphs. Thus ,tallness is factor
which is dominant over dwarfness in pea plant or the tallness & dwarfness are two
contrasting alleles of a trait height.
ll]PRINCIPAL OF DOMINANCE –
Mendel had already calculated that when a monohybrid cross is made betn. tall
& dwarf pea plant in F1 generation only tall plants appeared. But on selfing F1
progeny, both tall & dwarf plants appeared in F2 generation in the ratio 3:l. From here
it is clean that in F1 generation, tall ness conceals the dwarfness character so that only
tallness appears. Thus the character which appears in F1 generation is called as
dominant character & the character which remains unexpressed is called recessive
character.
Hence law of dominance states that in crossing betn organisms pure for
contrasting characters of a pair, only one character of the pair appears in the F1
generation.
In various cross experiments, the dominant character are transmitted from
parents to the offsprings. These characters are carried by the gametes containing the
hereditary units from one generation to the other. The hereditary units are called
‘factor’ or ‘determiner’ by Mendel. These are now called as genes. Every trait is
controlled by a pair of factors. Two contrast factors are called ‘alleles’.
In plants, so many characters were found to be dominant out of these some of the
characters are listed below which shows rightness of law of dominance.
DOMINANT
RECESSIVE
Sunflower – Branched habit
Wheat – susceptibility to rust
*
*
Unbranched habit
Immunity to rust
The law of dominance is equally applicable to the animals as well.
Eg. In Guinea pigs, homozygous pure black coated was mated with homozygous
pure white the offspring obtained in F1 generation will be black. This indicate that
black coat colour dominant over white coat colour.
Black coat
BB
!
B
*
Bb-F1-hybrid black
!
F1 * F1
Bb * Bb
white coat
bb
!
b
iii) Principle of segregation –
It states that the hybrids of F1 generation have two contrasting characters or
allelomorphs of dominant & recessive nature. These characters though remain
together but do not intermingle with each other & will separate during gametogenesis
( gamete formation) so that each gamete will have only one character i.e. dominant
or recessive . As the gamete produced contain only one ‘factor’ or ‘gene’ for one
contrasting character. Thus law of segregation in also called law of purity of gametes.
TALL
TT
!
(T)
*
DWARF
tt
!
(T)
Tt
!
- parents
- genotype
- gamete
-F1- tall but hybrid
l gamete information
T Segregation of two t
types of characters
In above cross, homozygous (pure) tall & homozygous (pure) dwarf pea plants, the
plants obtained in F1 generation were all heterozygous (hybrid) tall.
Though the factor (gene) for tallness ‘T’ & factor (gene ) for dwarfness ‘t’,
remained in close association in F1 generation, this was no mixing with each other.
When F1 will form gametes, two factors (genes) ‘T’ & ‘t’ separate or segregate from
each other & formed two kinds of gametes in equal number. i.e. one for tall (T) &
other for dwarf (t). The gametes obtained are pure for the particular gene.
2) Principle of independent assortment –
Besides monohybrid crosses, Mendel also considered dihybrid crosses in
which he took two pairs of contrasting characters at a time & noted the relation of
these characters during their inheritance.
One of the dihybrid crosses done by Mendel is the cross betn a homozygous
pea plant bearing yellow and round seeds & homozygous green wrinkled seeds pea
plant. In F1 generation hybrids with yellow or seeds are produced which on self
pollination produce for types of plants in the ratio of 9:3: 3:1.
i.e.Yellow round seeded plants – 9
Yellow wrinkled seeded plants-3
Green round seeded plant - 3
Green wrinkled seeded plant- 1
From the above result, Mendel formulated the law of independent which states that
when a cross is done betn parent differing in two or more pairs of contrasting
chatracters ,the inheritance one one pair of contrasting character is independent of the
other pair of contrasting character. The two characters are transmitted independently
in their own patterns.
Mechanism
Yellow Round
Seeds
YY RR
!
YR
*
YyRr
Male
YyRr
!
(YR) (Yr) (yR) (yr)


*
Green Wrinkled- P1
Seeds
yy rr - genotype
!
Yr – gametes
–F1-hybrid yellowround
Seeds
female – P2 (heterozygous)
YyRr – genotype
!
(YR) (Yr) (yR) (yr) – gametes
Solve by punnet square method
F2- 9: 3: 3:1: - phenotypic ratio
1: 2: 2: 4: 1: 2: 1: 2: 1: - genotypic ratio
To understand the mechanism involved in the indepedant assortment
of characters assume that homozygous pea plant bearing yellow & round seeds
is represented by RRYY (RR for roundness & YY for yellow colour of the
seed ), alleles, while homozygous plant with green & wrinkled seeds by ‘rryy’
During gametegenesis, ‘RRYY’ plant will produce gamete with RY alleles &
‘rryy’ plant will produce gamete with ‘ry’ alleles which after fertilization will
result in to a hybrid plant with ‘RrYy’ alleles. This plant will produce yellow &
round seeds because ‘R’ dominates ‘r’ & ‘y’ alleles dominants Y alleles.
During gamete genesis in this hybrid plant,form possible gametes can be
produced is ‘RY’ ‘Ry’ ‘rY’ & ‘ry’. Thus, four type of alleles are associated
independently in the four types of gametes, which on fertilization can produce
sixteen plants in F2 generations .
Out of sixteen plants 9 plants bear yellow round seeds, 3 yellow wrinkled
seeds, 3 green round seeds & one green wrinkled seeds giving 9; 3; 3;1; this
proves that law of independent assortment & showed that each pair of
contrasting character behaves independently & bears permanent association or
relation with particular character.
Back cross & test cross – when F1 hybrid are crossed with one of the
two parent then such a cross is called back cross. In this type of crosses.
Dominant character the recessive characters appear in the progeny. On the other
hand, if the hybrid (F1) is crossed with recessive parent only,then both
dominant & recessive characters appear in equal numbers. Is l:l ratio . This type
of back cross It is called test cross , it is used to test whether the individuals is
homozygous or heterozygous.
Eg. Monohybrid cross
Dihybrid cross
Cross betn homozygous tall pea plant
cross betn tall & smooth seeded
(DD)& homozygous dwarf pea plant
plant & dwarf & wrinkled seeded
(dd) then are obtain offsprings in ratio l:l
plant, in progeny we get form phe
,
-notypic ratio of l:l:l:l.
Incomplete Dominance & Co- Dominance
Incomplete dominance – The law of dominance is not always found to be correct as
there are many examples where the complete dominance is absent. The familiar
cross of red flowered pea plant & white flowered pea plant is taken for example.
Here after crossing the two pure variety, the F1 plants do not show red colour but
pink colour of flowers appears. Thus the heterozygous plant (Rr) does not show the
complete dominance of red colour in flower what happens here is that red colour is
not able to dominance white completely resulting in the appearance of intermediate
colour, the pink.In F2 generation too, one pure red, two pink, & one white coloured
flowers are seen. Such inheritance is also called intermediate inheritance & the
factor or genes. For such characters are called intermediate genes or factor. It is
also called as partial inheritance or blending inheritance. There are many examples
of this condition in plants as well as animals.
In 4”0” clock plant (Mirabilis jalapa), the incomplete dominance is seen with
flowers colour. The pure variety have red or white flowers but on crossing the two
varieties, F1 generation shows only pink colour (heterozygous on selfing F1 in the
F2 generation one pure red, two pink & one pure white flower are (hybrid)
generation show dominant character which is incomplete. The ratio obtained in F2
generation in completely modified is lizil. This show that phenotypic & genotypic
ratios are similar.
Co- Dominance – co – dominance is a state in which each allele of a
gene expresses an effect in a heterozygous individual. In co – dominant & recessive
alleles lack then dominant & recessive relationships & both the genes express their
expression independently.
Eg. Roan colour in cattle.
When a red bull is crossed with a white cow, the F1 hybrid obtained are roan
in colour .The roan colour is caused by a mixing of two types of hairs is red & white
hairs in a mosaic fashion. No hair has intermediate colour of red & white. When F1
roan coloured hybrids inbred, the F2 generation obtained consists of 1 red ,2 roan & 1
white. The F1 hybrids obtained in this case are roan coloured because the gene for the
red colour & the gene for the white colour both have about equal effect. So, there
being no dominance of one character over the other.
HUMAN GENETICS
Genes control various traits in an organism through a control exercised on the
development processes. Such a control is due to synthesis of proteins which is
underdirect control of genes. Some of these proteins synthesised by genes are
enzymes & control biosynthetic pathways. That genes are express themselves
through synthesis of enzymes was demonstrated for the first time in 1941 by G. W.
Beadle & E.L. Tatum ( both Noble Prize winners of 1958 ). They both proposed a
concept called one gene-one enzyme hypothesis. Such a hypothesis means that if in a
biosynthetic pathway several steps are involved, each step is controlled by a specific
enzyme, which is synthesized under the control of a specific gene.
Phenylketonuria & alkaptonuria in his book “Inborn errors of
metabolism.” These there diseases are associated with the metabolic break down of
phenylalanine.
Phenylketonuria (PKU) / phenyl ketone uric imbecility –
A.E. garrod (1858-1936) was an English physician, who described
various physiological abnormalities of men that appeared to be inherited. This is
because of absence of specific enzymes which were present in normal persons.
“ Chart showing phenylalanine tyrosine metabolism and cause of PKU”
Phenylalanine is a part of almost all protein foods we eat. During digestion
the proteins breaks down into their component amino acids. Thus phenylalanine
becomes free in the digestive tract. It is absorbed along with other soluble food
products & can pass in to cell, it may follow one of the three course so for depending
upon which enzyme acts upon it. It may be converted into another amino acid,
tyrosine or it may be converted into phenyl pyretic acid.
In normal persons the enzyme phenylalanine hydroxyl’s catalysis the
conversion of phenylalanine into very similar amino acid tyrosine. But there are some
people who genetic reasons, lack this enzyme. The recessive gene P2, for instance,
when homozygous (P1,P2), causes a fair lure in the production or functioning of this
enzyme. The persons who lack this enzyme cannot convert phenylalanine into
tyrosine in the regular way, but large concentrations of it are accumulated in The
blood, the cerebra-spinal fluid, & the wine. In normal persons some phenylalanine is
converted into phenyl pyruvic acid, but in persons lacking phenylalanine hydroxylase
Enzyme excessive amount of this substance ( phenylpyruvic acid) are produced &
excreted in the urine. Due to the presence of the ketene phenylpyruvic in the urine, the
condition is known as phenylketon uria or PKU. The persons with the PKU are also
called the phenyl pyruvies.
Normal – P1,P1( produce more enzyme )
PKU trait/ carrier – P1,P2 (heterozygous carrier) (produce less enzyme)
PKU – P2,P2 (failure in producing enzyme )
1 to 2 mg/ 100 ml – normal level
- plasma phenylalanine
15 to 63 mg / 10 m- PKU
30 mg / 100 ml – normal person
- urine
300 to 1000 mg / 100 ml - PKU
Children suffering from this disease are known as phenylpyruvic idiots. High
quantities of phenylalanine in body tissues interfere with the development of the brain
& cause mental retardation or idiocy.
PKU – IQ below 20 (idiot) – 64%
Below 50 (imbecile) – 96 %
Bet (n) soft to – 4 %
Children suffering from PKU can be rectified by giving phenylalanine free from
protein food. It can be detected carrier gene for PKU. By cheeking the level of both
phenylalanine & tyrosine from plasma.
GENETIC COUNSELLING –
It is defined as a process of communication that deals with human problems
associated with the occurrence or risk of a genetic disorder in a family.
The genetic counselling includes education of genetic diseases as well as
psycho- social counselling. It deals with issue directly or indirectly involved with
genetic disease. The genetic counsellor gathers information regarding family life
history of the patients. He educates the patient about general genetic principals related
to disease risk both for themselves & others in the family. He assists in determining
the role of genetic testing for the individual & family. Thus, the approach to genetic
counselling has important ethical, social, & financial implications.
GENETIC COUNSELLING IS OF TWO TYPES –
1) Prospective genetic counselling – In this the heterozygous individuals
for any defect is identified & adviced not to many heterozygous individuals of
same gene.
2) Retrospective genetic counselling – such kind of counselling is for
those family members where hereditary disorders have already occurred.
a) Sickle cell anaemia – parental diagnosis is now available for couples at
risk of producing a child with SCA. DNA from foetal cells can be directly
examined & the presence of sickle call mutation can be accurately diagnosed.
Genetic counselling to such couples is most helpful to prevent the birth of
defective children.
b) Amniotic fluid & preparing kargotypes from cells derived from the foetus &
floating in this fluid, the sere of developing feetrs can be identified.
When a pregnant women is known to have a chance of bearing a child
with a genetic disorder, it may be desirable to diagnose the condition in the foetus.
This can be done by taking some cell. From the foetus by drawing a few millilitres of
amniotic fluid with the help of a hypodermic needle, the technique is called
amniocentesis hydroxylase enzymes. And is usually performed at 15 th week of
pregnancy, to allow enough time for safe abortions. The amniotic fluid has free cells
of foetal origin, which can be cultured & tested in various ways eg. Kargotype
,enzyme production, restriction site pattern analysis of its DNA or quantitative PCR.
A large number of disorder is detected through such an antenatal diagnosis, abortion
of foetus can then be recommended.
With in 18 work period disease
can be identified.
(Amniocentesis & antenatal –natal diagnosis)
c) PKU genetic disorder – (described earlier )
d) Haemophilia and colour blindness – In sex linked inheritance a
mutant gene ‘X’ on chromosome in males will express it self reading as there
is no normal allele, while a mutant gene on X chromosome in female will not
express itself in the presence of the normal allele. Eg. Haemophilia “ if an
affected male marries a normal female, the gene is transmitted to all the
daughter will be carriers & 50% normal. 50% of her sons will be normal &
50%affected. Genetic counselling in such instances in helpful.
e) Erythroblastosis foetal is – this disease occurs mainly in new born in
farts or children having Rh-positive blood group whose mother is Rh-ve &
father is Rh+ve .in such a case the blood group of a child is Rh+ve which is
due to the inheritance of the Rh-antigene from the father. Sin a rh+ve
condition is dominant over Rh-ve condition, the blood group of the child
becomes Rh+ve .
During pregnancy a connection called placenta is developed
bet (4) .embryo & the mother. Through the placental blood vessels months blood
circulates in embryo. At the first 4 months of pregnancy only mother blood which
is Rh-ve in present in embrgo.
At 5th month of pregnancy the embryo starts producing its own
blood which is Rh-ve. Some red blood cells of embryo escape in mother
circulation. Thus, mother bloods starts synthesizing antibodies at the end of 5th
month or during 6th month onwards. Against the R.B.C.S. of embryo. These
antibodies them enter the embryo through the month blood & destroy the R.B.C.s
of embryo by agglutination. The clumps of dearl R.B.Cs gather in liver & block
the sinusoids. The outflow of bite stop & cause jaundice in the embryo.
The first child of Rh+ve father & Rh-ve mother is born normal
because, this case during pregnancy period. The antibodies produced by the
mothers blood are less in number & .. fail to destroy the embryo. But later on in
the 2 nd & in the next pregnancies the blood of the mother produces antibodies
right from the initial stager of pregnancy & reaches to maximum strength , thus
the number of antibodies produced by the mothers blood in all these pregnancies
is higher than the first pregnancy. This is the reason due to which the second
Rh+ve child born is abnormal suffering from the disease jaundice & anaemia. The
disease is know as every throblasters is foetal is which cause the death of the
child.
When both the parents are Rh-ve or if the mother is Rh+ve them
there is no danger to the child.
RIBOSOMES
The factory of protein synthesis
1) Introduction –
The Ribosomes are small, dense, rainded and granular particles of the
ribonucleoproteins. Ribosomes are located everywhere in the cell i.e. In the
nucleus, on the nuclear membrane, in the cytoplasm, on the cell organelles like
ER, in the cell organelle like mitochondria & chloroplast.
Ribosomes are described as factories of proteion synthesis. Ribosomes
were frist discovered by Claude (1941) and named them as microsomes. Palade
(1995) named them as ribosomes. For the mapping of ribosomes Dr.
Ramkrishnan got Noble Prize in October 2009.
The number of ribosomes in the cell is directly related to the RNA
content of the cell.
2) Ultra structure of ribosome
Ribosomes are spherical bodies. Each ribosome consists of two subunits, namely
a large subunit and a small subunit. The subunits occure separately in the
cytoplasm. They join together to from ribosomes only at the time of protein
synthesis. Generally 5 or more ribosomes line up & join an mRNA chain, such a
string of ribosomes is called polyribosome or polysome.
The small subunit holds the mRNA during protein synthesis.
The large subunit has two slots, namely P-site and A-site. The P-site carries a
tRNA containing polypeptide chain. The A- site carrier a t RNA containing
activated or charged amino acid.
Fig. polyribosome in action.
3) Types of Ribosomes
According to the size & sedimentation coefficients 3 types of ribosomes
have been reported. They are 70s, 80s and 55s ribosomes.
1) 70s ribosome / prokaryotic ribosome-
The 70s ribosome is found in prokaryotic cells. It has molecular wt. 3*10 (6)
Daltons .it is composed of rRNA & proteins.
Fig. diagram to show the composition of prokaryotic ribosome.
2) 80s ribosome / Eukaryotic ribosome.
The 80s ribosome found in eukaryotes. It is larger in size. It has mol. Wt. of
5*10(6) Daltons. It is composed of rRNA and ribosomal proteins.
Fig. diagram showing composition of eukaryotic ribosome.
3) 55s RNA- mitochondria & chloroplast ribosome.
55s ribosome is present in cell organelles, such as mitochondria and
chloroplast. 55s ribosomes are the smallest ribosomes, they are made up of large
subunit 40s and small subunit 30s.
4) Association & Dissociation of RibosomesThe subunits remain freely in the cytoplasm. In the begining of the process
of protein synthesis the two subunits are unite together & at the end of protein
synthesis they dissociate. Similarly two ribosomes unite together to form a dimer.
Many ribosomes link together to from polyribosome. The association of sub
units as well as ribosomes occure at a high concentration of Mg++.
Fig. Association of ribosomal subunits.
5) Functions of Ribosome
Ribosomes have the following functions1) Protein SynthesisRibosomes play an important role in protein synthesis.
Two or more ribosomes simultaneously take part in protein synthesis .During
Protein synthesis, the two subunits link together on m RNA. Thus many ribosomes
are attached to the mRNA, forming polyribosomes.
2) ProtectionRibosomes are protective in function. The strand of mRNA passing through
the ribosomes is protected from the enzyme action (i.e. nucleases). Similarly
polypeptide chains passing through the channel between the subunits are protected
from the action of protein digesting enzymes (i.e. proteases).
POLYTENE CHROMOSOME
A special chromosome
( Poly- many, Tene – arms )
Polytene chromosome have the following salient features –
1) It was discovered by Balbiani in 1881.
2) It was found in the salivary gland cells of chironomus larva or drosophila
larva ; hence it is also called salivary gland chromosome.
3) It is larger in size eg. In drosophila, it is 1000 times larger than somatic
chromosome.
4) The larger size of the chromosome is due to the presence of many
longitudinal strands, called chromonemata. Hence they are also called
polytene chromosomes ( many stranded)
5) The many stands of the giant chromosome are due to repeated divisions of
the chromosome without the cytoplasmic division, this type of division is
called endomitosis.
6) The polytene chromosome contains two types of transverse bands, namely
dark bands & inter bands. The dark bands are darkly stained with nuclear
stains. The dark bands contains more DNA & less RNA. The inter bands
contains more RNA and less DNA.
7) The bands of polytene chromosomes become enlarged at certain times to
from swelling, called puffs or Balbiani rings. The formation of puffs is
called puffing. In the region of puffs the chromonemata uncoil and open out
to from many loops.
The puffs indicate site of active genes, when m RNA synthesis takes
place.
Fig. polytene chromosome of salivary gland of male drosophila.

Functions of polytene chromosome –
1) To carry genes – The main function of polytene chromosome is to
carry the genes which control the physiology of an organism. These
Genes are of DNA molecules.
2) Protein synthesis – The polytene chromosomes also help in protein
synthesis indirectly. Nucleolus contains RNA. This RNA serves as a
means of transmission of genetic information to the cytoplasm,
leading to the form action of specific protein.
CENTROMERE AND TELOMERE
A) Centromere –
Centromere is the most important part of chromosomes. It is a
constricted or notch like part, where the arms of chromosomes meet. Centro mere is also called kinetochore. During the cell division spindle fibres attaches
to kinetochore (also called kinetochore microtubules) and sister chromatids
pulls apart at anaphase.
According to the position of centromere, the chromosome are of 4 types Telocentric
Acrocentric
Sub – metacentric
Metacentric
Generally only one centromere is present in chromosome, which is called
monocentric chromosome. But some times two or many centromeres are
present called Dicentric or polycentric respectively. The dicentric & polycentric
cases are rare & they will be not survive. Sometimes centromere is absent ,the
chromosomes called acentric. Acentric chromosomes not attached to the spindle
fibres & remains in the cytoplasm.
B) TelomereIt is the terminal region of chromatid. Telomeres differ in structure &
composition from the rest of the chromosome.
When chromosomes are broken, due to the effect of some physical
mutagen, the broken ends (without telomeres ) becomes sticky & these two
broken ends can fuse with each other i.e. the two normal ends having telomeres
never fuse with each other & the original structure of chromosome is preserved/
maintained.
Telomeres are specially modified regions of chromosomes for the
attachment to the nuclear envelope. Telomeres contains telomerase enzyme
which has characteristics of reverse transcription.
Fig. chromosome showing telomeres & centrometes.
ENDOPLASMIC RETICULUM
A site of protein synthesis
1) INTRODUCTION –
ER was first observed by Porter ( 1945)
It occurs in all eukaryotic cells except erythrocytes (RBCs) of mammals.
ER is absent in prokaryotes.
Well developed in the cells of liver , pancreas etc.
It is a network of memb. bound cavities distributed throughout the
cytoplasm.
Morphologically ER is composed of three types of structures1) Cisternae – These are long , flattened and usually unbranched tubules.
They are arranged parallel to each other. They are having
uniform width throughout.
Thickness is 40-50 Mm.
Outer surface is having ribosomes.
2) Vesicles – Rounded or oval
Diameter is varies about 25 to 500 Mm.
The vesicles are engaged in protein synthesis, in hepatic &
pancreatic cells.
3) Tubules - small smooth walled or rough, branched diameter is about 50190 Mm.
They are found in the cells which are busy in the
Synthesis of steroids like cholesterol, glycerides & hormones.
Arrangement varies in diff. cells.
They are also found in pigmented epithelial cells of
ratina.
3) Ultrastructure
On the basis of presence or absence of ribosomes, the ER is of two
types1) RER – It the ribosomes of about 100 to 140 A0 diameters are present in
large number on wall of ER ,then is called RER.
Ribosomes are always present on outer surface of ER. RER is
high in ribonucleic acid (RNA)
RER contains about 40% RNA & 60% proteins i.e.
Ribonucleoprotein.
Ribosomes are imp .in protein synthesis.
2) SER – If the ribosomes are absent on outer surface of ER, it is called SER.
Membrane of SER is contineous at some places with the mem.
of Golgi or PM. It forms complex lattice of dimater of about 50 to 100 Mm.
SER present in the cells which are active in synthesis of steroid compounds
eg. Cholesterol glycerides & hormones .
3) Functions of ER1) Mechanical support ER forms a skeletal network / framework in cytoplasm & divide
fluid content in compartments.
2) protein synthesis –
RER plays important role in protein synthesis.
ER also helps in transport of proteins to the outside of cells.
3) Glycogen synthesis & storage –
SER plays imp. role in the synthesis of glycogen (glyceraldehydes)
i.e. glycogenesis, with the help of simple sugars& stored in ER.
4) Enzymatic activitiesER memb. shows various synthetic & metabolic activities within
The cell.
Varios enzymes eg. NADP diaphorase ,NADH –cytochrome
Oxidase, Mg activated ATPase, Glucose 6-phosphatase etc.
5) Lipid synthesis & storage
ER is the site of triglyceride formation (only SER)
Proteins & phospholipids – synthesized in RER.
ER functions as intracellular transport & storage of lipids.
6) Detoxification Memb. of SER have several enzyme system, which acts on toxic
Substance & destroy them.
7) Synthesis of cholesterol & steroid hormones 8) Formation of nuclear membrane ER is the source of origin of NM during cell division.
9) Muscle contraction & relaxantion
ER helps the muscle contraction & relaxation with the help of
Calcium ions.
GOLGI COMPLEX
A secretory granules of cells.
1) INTRODUCTION
Golgi complex is a cluster of smooth membranes associated with the
endoplasmic reticulum. It was first described by Camilo golgi (1898) in the nerve
cells of barn owl. The golgi complex has been variously named as golgy body,
dictyosome, lipochondrion, internal reticular apparatus, canalicular system etc. by
various workers. The term dictyosomes is used for the golgi material of
invertebrates & plants.
The golgi complex is absent in prokaryotic cells, certain fungi, sperm
cells of bryophytes & pterdophytes and sperms and RBCs.
Animal cell contains only one golgi complex. Plant cells usually
contain hundreds of golgi bodies. The golgi complex is difficult to observe in living
cells, because its refractive index is similar to that of matrix.
2) ULTRASTRUCTURE OF GOLGI COMPLEX
The golgi complex is morphologically very similar in both plant & animal cells.
Electron microscopic observations of golgi complex by several workers states that
it is made up of three membranous components – 1) flattened sacs or cisternae.
2) small tubules/ vesicles
3) large vacuoles.
1) Flattened sacs or cisternae Cisternae are flattened, plate like closed compartments. They are held in
parallel bundles or stacks one above the other size & number of cisternae exhibit
variation. The number is usually between 4 to 8 in most animal & plant cell types.
In euglena, the number may go up to 20 the animal cells may contain about 5 to 6
golgi cisernae .The cisernae have two well defined faces namely convex & the
concave. The concave is the mature or distal face while the convex is the immature
or proximal face.
The relative lengths of cisternae shows great variations. All cisternaes are
interconnected ,due to which the golgi complex appears as a system of branched
tubules. The cisternae are stacked together & large number of small vesicles remain
associated with each stack of cisternae. Each stack of cisternae has two faces,
namely cis face & trans face. The entry face receives vesicles from endoplasmic
reticulum, it is called cis face. The second face is trans face or exit face from where
the golgi vesicles leave the complex.
2)Small Tubules & Vesicles –
From the peripheral area of cisternae arise a complex flat network of tubules.
The vesicles are small droplet like sacs. They remain attached to the tubules at
the periphery of the cisternae. The vesicles are of three types –
a) transitional vesicles
b) secretary vesicles.
c) Clathrin – coated vesicles
3) Large vacuoles The large vacuoles are clear & lie at the edge of the golgi complex.
They represents modified & expanded cisternae in which the two membranes
have become widely separated & the vascular space enlarged. This vacuoles
are filled with some amorphous or granular substance.
3) FUNCTIONS OF GOLGI COMPLEX
1) Formation of Acrosome during spermiogenesis Spermiogenesis means maturation of sperm i.e. conversion of spermatids to
spermatozoa. Golgi complex play important role in the formation of acrosome
which contains hydrolytic enzymes.
2) Role in secretionGolgi complex plays very important role in secretion of
substances like mucus, sweat, tears, hormones, antibodies, enzymes etc.
various
3) Role in cell – plate formationDuring cytokinesis, the golgi vesicles accumulate in the equitorial plate
& helps in the formation of cell plate.
4) golgi complex stores lipids & proteins .
5) primary lysosomes are formed from the golgi membranes the same way as
the secretary vesicles .
6) golgi complex helps in the intercellular translocation of materials.
7) pigment formation
In many mammalian tumor ( cancer) cells, the golgi complex has been
described as the site of origin of pigment granules i.e. melanin.
8) milk protein droplet formation In the loctating mammary gland of mice ,the protein droplets are
produced which are related with golgi complex.
LYSOSOME
1) INTRODUCTION
Lysosomes are recently discovered organelles of the cell. They are
observed in liver cell. They were first named as percanalicular bodies depending
on their location. They are renamed as lysosomes. By De DUVE in 1995. The
centrifugal properties of lysosome somewhat intermediate between those of
mitochondria & microsomes.
Lysosomes have high content of acid phosphatase and other hydrolytic
enzymes .Due to their enzymatic properties, they were named lysosomes (lysis –
dissolution soma -body). These organelles contain digestive enzymes capable of
lysis or digestion of food molecules. Therefore lysosome is a lytic body present in
the cytoplasm
Lysosomes are present in both animal & plant cells. They are absent in
bacterial cells &mature mammalian erythrocytes (RBCs)
2) Ultra structure of lysosome –
lysosomes are difficult to identify under electron microscope, because
they do not have characteristic shape or structure. Generally they are globular
structures. They remain filled with dense material & are bounded by single unit
membrane. Since the size & shape of lysosome vary from cell to cell & time to
time i.e. they are polymorphic.
On the basis of following criteria, lysosomes can be identified. They are
1) It should be bound by a limiting membrane.
2) It should contain two or more acid hydrolases.
If the enzymes of lysosome are released, because of their hydrolytic nature,
they digest & dissociate the cell, due to which the lysosomes are called
sucide bags.
Generally lysosomes are traced in four formsa) Primary lysosome
b) Secondary lysosome
c) Residual or post lysosome
d) Autophasic vacuoles
fig. polymorphism of lysosomes.
a) Primary lysosomesthese are also called the true, pure or original lysosomes having a single unit
membrane containing enzymes in the inactive forms. It is possible that the golgi
complex buds of primary lysosomes containing hydrolytic enzymes.
b) secondary lysosomes- (Digestive vacuoles)
These are formed by the fusion of primary lysosomes with phagosomes
(phagosome –A vesicle formed by phagocytosis or pinocytosis) . They contain
engulfed material & enzymes. The material is progressively digested by enzymes.
c) Residual or post lysosomesthe secondary lysosomes with undigested wastes are called residual
lysosomes. The digested material is diffused into cell cytoplasm through the
lysosomal membrane.
d) Autophagic vacuoles – the autophagic vacuoles are formed when the cell feed
on its intracellular organelles, such as the mitochondria & endoplasmic reticulum
by the process of qutophagy.
The autophagic vacuoles are formed when the cell feeds on its own kinds
organelles.& during some physiological & pathological conditions. Eg. During
starvation of organism many autophagic vacuoles developed. In the liver cells they
feed on the cellular components.
3) Functions of lysosomes 1) Extra cellular digestion Lysosomal enzymes may be released outside the cell where they take
part in the hydrolysis of extra cellular material. Eg. The lysosomes of sperms
discharge their enzymes digests the membranes of ovum & form penetration path in
ovum for the sperms.
2) Intracellular digestion Digestion of substances within the cell is called intracellular digestion
.intracellular digestion may involve autophagy or heterophagy.
3) Autolysis
In certain pathological conditions the lysosmes start to digest the
various organelles of the cell, which is know as autolysis, or cellular autophagy.
4) Chromosome breaksRibosome contains the enzyme deoxyribonuclease (DNA ase). This
enzyme causes chromosomal breaks & also their rearrangement.
5) Removal of dead cells The lysosome helps in the removal of dead cells in tissues.
6) Fertilization Penetration of sperm nucleus by breaking egg membrane by
lysosomal enzymes is the key step in fertilization.
7) Role in Metamorphosis The large amount of larval tissue is destroyed during
metamorphosis of insects & amphibians. Eg. Degenerate of tail of frog tadpole.
8) role during cell division During cell division, the repressors of the cytoplasm are trying to
inhibit the cell division, but lysosomes secrete some depressors which destroy the
repressors & continue the cell division.
9) Useful during germinationDuring seed germination, the lysosomes in embryo cells are
involved in the hydrolysis & removal of protein & starch, required for growth of
seedlings.
CYTOSKELETON
The skeleton of the cell.
1) INTRODUCTION
The ability of eukaryotic cells to adopt a variety of shapes & to carry out
co-ordinated & directed movements depends on the cytoskeleton. The cytoskeleton
extends throughought the cytoplasm & is a complex network of three types of
protein filaments – 1) Microtubules
2) microfilaments ( or actinfilaments ) and
3) Intermediate filaments
The cytoskeleton is also refered to as cytomusculature, because it is directly
involved in movements such as crawling of cells on a substratum.
The existance of an organized fibrous array or cytoskeleton in the structure
of the protoplasm was postulated in 1928 by Koltzoff.
The main proteins that are present in the cytoskeleton are tubulin (in
microtubules) ,Actin , Myosin, Tropomyosin & other (in microfilaments) and
keratins, vimentin desmin & lamin (in interdiate filaments ).
2) Microtubules – structure –
Microtubules were first of all observed in the axoplasm of the myelinated
nerve fibres by Robertis& Franchi(1953). They called them neurotubules.
Microtubules are found in every cells with rare exceptions such as the
human erythrocytes, microtubules are found in all eukaryotic cells either free in the
cytoplasm or forming part of centrioles, cilia & flagella. Microtubules are located
in cytoplasm, in nerve cells, in sensory cells in axopodia of protozoa, in fiagella &
cilia of animals etc.
Structurally microtubules are long & hollow cylinders composed of many
subunits, called protofilaments. The number of protofilaments in microtubules is
variable . A T. S. of cytoplasmic microtubule shows 13 subunits or protofilaments.
They lie parallel to the long axis of the microtubule .
The outer diameter of the cylinder of the microtubule is about 250 A0 ,while
the hollow core is about 150 A0. The thicknees of the wall of cylinder is about 50
A0. The length of microtubule varies from few microns to several microns, while in
some cases , the microtubules are about several mm. long.
The protofilament is composed of a series of globular protein (tubulin)
units. Each unit looks like a string of beads and is about 50 A0 *40 A0 in size.
Under normal physiological conditions, the tubulin is dimer, made- up of two
similar polypeptides. The two units of tubulin dimer are called < -tubulin and B –
tubulin .
These two units are arranged alternately in the protofilament. The
mol.wt.of < -tubulin is 55000 Dalton & of B-tubulin is about 57000 Dalton. The
amino acid composition of these two units are similar. The tubulin shows helical
structure with 13 tubulin molecules per turn of the helix.
In the protofilament, with the tubulins there are about 20 to 25 secondary
proteins, called microtubule- associated proteins (MAPs) have been reported.
Microtubules may be labile or stable. Labile microtubules are easily disrupted by
treatment with inhibitors such as colchicine & vinblastine.
Fig. A) cross section of cytoplasmic microtubule showing 13 protofilaments.
B)surface view of microtubules showing probable arrangement of < & B –
tubulin units.
3) Functions of microtubules –
1) Maintanance of cell shape Microtubules are rigid structures, which work as a supporting
framework or cytoskeleton & give shape to the cell. They also maintain shape of
long processes like cilia & flagella.
2) Morphogenesis ( change in the cell shape ) Microtubules changes the shape of the cells during cell
differentiation. Eg. Elongation of the cells in the lens of eye, nucleus of the
spermatids during sperm formation.
3) Sensory transduction Many sensory cells ,in association with nerve fibres are provided
with microtubules.
4) Transport of cellular material Various proteins & other substances synthesized in the cell are the
transported to the extracellur matrix or to the other cells with the help of
microtubules.
5) Chromosomal movements in cell division During mitosis or meiosis, the spindle fibres appeared are nothing
but the bundles of microtubules. The shortening of kinetochore microtubules &
elongation of microtubules of contineous fibres provide the force for chromosome
movement during anaphasic stage.
6) Movement of cilia & flagella The central axis or axoneme of cilia & flagella is made up of the
microtubules. These microtubules are involved in the movement of cilia & flagella.
PLASMA MEMBRANE
1) INTRODUCTION The plasma membrane may be defined as thin, elastic semi permeable living
membrane that serves as a boundry for the cytoplasm. The term plasma membrane
was coiled by Nageli in 1855. Plasma membrane is otherwise called cell membrane or
plasmalemma.
Plasma membrane is the outer limiting membrane in all animal cells. But in plant
cells and bacterial cells, it is present below the cell wall.
Plasma membrane is formed of chemicals, these chemicals are arranged in a
definite pattern. Different models were proposed to explain the structure of plasma
membrane i.e.
1) Trilaminar model/ unit membrane –By Robertson (1959)
2) Bimolecular leaflet model – By Danielli & Davson (1934)
3) Lattice model – By Wolpers. (1941)
4) Fluid mosaic model – Singer & Nicolson (1972)
5) Micellar model – By Hillier & Hoffman (1953)
Out of these, the fluid mosaic modal proposed by Singer & Nicolson
( 1972) is universally accepted.
2) ULTRASTRUCTURE & PLASMA MEMBRANE The fluid mosaic modal was proposed by S.J. Singer and G.L.Nicolson of
the California University in 1972. The structure & arrangement of the membrane in
this model are different from those of previous model of Davson & Danielli and unit
membrane concept of Robertson.
The fluid mosaic model is now widely accepted as best explaining properties
of the membrane. This model assume that all biological membranes are quasifluid
(semifluid) structures, where the lipid molecules form a contineous bilayer in which
globular proteins are embedded.
The protein molecules are compared to the icebergs floating in the sea of
lipid bilayer giving a mosaic appearance. The membrane proteins are considered to
be of two types namely extrinsic (peripheral) and intrinsic (integral) proteins. The
extrinsic proteins are found entirely on the outer side of the lipid bilayer while the
intrinsic proteins may penetrate partially or fully into the lipid bilayer. The lipid
membrane provides the permeability barrier.
Chemically all membranes are made up of lipids & proteins. These
molecules are held together in a thin sheet by non – covalent bonds. In addition to
lipids & proteins, membrane also contains carbohydrates.
- The lipid molecules are insoluble in water but dissolve readily in organic
solvents. (eg. Alcohol, Enter etc.) . Lipids are of phospholipids, glycolipids &
cholesterol.
- The basic structure of biological membrane is determined by lipid bilayer
while their specific functions are carried out largely by proteins. These
-
proteins are – Peripheral ( extrinsic) proteins, Integral ( intrinsic) proteins &
Lipid anchored proteins.
Carbohydrates are present only in the plasma membrane & no carbohydrate is
located at the cytoplasmic or inner surface of the plasma membrane.
Carbohydrate are in the from of glycoproteins.
3) FUNCTIONS OF PLASMA MEMBRANE 1) Mechanical support – PM gives shape to the cell. Protects cell
contents & keep the cell contents in place.
2) Transport – PM regulates traffic of molecules into & out of the
cell.
PM acts as semipermeable barrier between cell and extra
cellular matrix.
PM is selectively permiable i.e. it is not permeable to all
types of solutes. This transport is may be active or passive .

Passive Transport – This types of transport doesn’t requires
energy. It occurs in following ways.
a) SIMPLE DIFFUSION – It is a process in which a substance
moves from a region of higher concentration to the region of
lower concentration. The difference between two concentration
is called concentration gradient.




Osmosis – water molecules moves radially through a
semipermiable membrane from a region of lower solute conc.to a
region of higher solute conc.
The process of osmosis is demonstrated by placing a
cell into a solution containing different solute concentrations.
If there is higher solute conc. outside the cell – Hypertonic. In
such condition cell losses water by osmosis & shrinks.
If lower solute conc. outside the cell – Hypotonic . Cells swells or
rapidly gain water.
If solute conc. is same inside the cell & outside the cell – Isotonic
.No loss or gain of water .Cell shape constant.
b) FACILITATED DIFFUSION It differs from simple diffusion as it require facilitative transporter
for transport across membrane. This process is specific &
rate of transport of molecules across memb. is greater.

ACTIVE TRANSPORT – Active transport requires engrgy
(ATP) because ,this type of transport takes place against conc.
gradient i.e. form lower conc. to high conc.
3) CELL RECOGNITION & ADHESION -
The sites of cell recognition lies on the surface of PM. Because
of this property the mammalian WBCs recognizes the
foreign cells like bacteria.
4) HORMONE RECEPTORS PM provides receptors for peptide hormones. Hormonereceptor complex formed at PM & then hormone enters into the
cytoplasm.
5) SECRETION Cell secretion is a process where ribosomes & ER,golgi,
secretory vesicles are involved. Release of secretory products
takes place through PM.
6) ENERGY TRANSDUCTION Membranes are closely associated in the process by which
one type of energy is converted to other type seen in membrane of
chloroplast.
7) ENDOCYTOSIS & EXOCYTOSIS !
!
Process of engulfing Reverse process of endocytosis
food particles or
eliminates undigested material.
foreign materials


Pinocytosis – cell drinking (pinosome)
Phagocytosis – cell eating (phagosome )
8) Chemoreception It is a response to chemical stimuli. Specific receptor proteins
are involved in this phenomenon .Here, PM Plays very important
role.
9) Transmission Transmission of nerve impulse.
Transmission of impulse for contraction of muscle cells.
MITOCHONDRIA
The power house of cells.
(Mitos- filament, chondros – granules)
A) Introduction – The mitochondria are thread – like or granular cytoplasmic
organelles. They contain many enzymes & co- enzymes which are responsible for
energy metabolism. They are described as power – house of cells. Mitochondria are
found in aerobically ( in the presence of 02 ) respiring cells, of plant & animal, but not
in bacteria.
Mitochondria were first discovered by Flemming & Kollikar (1882). These
organelles were first called bioblasts by Altmann. Later the term mitochondria was
introduced by Benda (1898).
B) Shape – The mitochondria may be filamentous or granular in shape. The
shape of mitochondria may change from one to another depending upon
physiological conditions of the cell. They may be rod – shaped, club – shaped, ring
– shaped, rounded or vesicular.
C) Ultra structure Mitochondria are distributed uniformly throughout the cytoplasm.
During cell division, they are concentrated around the spindle,generally they
accumulate at the region of higher activity, i.e. at the site of active muscles.
Number of mitochondria < metabolic activity of the cell.
Typical mitochondria is about 15,000 A0 long & 5000 A0 diameter.
Mitochondria is composed of two membranes i.e. outer membrane & inner
membrane,.The outer membrane is contineuous while the inner membrane is folded
, called as crista. In between the outer and inner membrane there is intermembranous space.
The mitochondria also shows two sites i.e. M-site or matrix site & the
C-site i.e. cytosolic site. Majority of the functions of mitochondria are accumulated
to the M-site.
The matrix of mitochondria contains – circular DNA, ribosomes , Ca+2
& Mg+2 granules, RNA, proteins,F1- particles ( also called oxysomes ) or ETP
(electron transport particles).
Mitochondrial matrix contains number of enzymes, eg. All the enzymes
required for Glycolysis & Kreb’s cycle are present in the mito . matrix. The F1
particle or oxysome is the site of ATP synthesis through the enzyme ATP synthase.
The most important feature of mitochondria is the presence of F1
particles at the M-site. The F1 particle shows different parts as head, middle piece/
stalk and base. The height of F1 particle is 160 A0. The base of F1 particle is
embedded in the inner membrane.
D) Chemical composition of mitochondriaAs the mitochondria are the membranous organelles, each membrane
consists of specific chemical composition.
The membrane of mitochondria is made – up of two main substancesProteins
Lipids
( 65 - 75 % )
( 25 – 30 % )
!
!
Insoluble in water
contains
( hydrophobic )
90 % cholesterol & phospholipids
5 – 10 % free fatty acids.
Besides proteins & lipids, mitochondria also contains 0.5 % RNA and small
amount of circular DNA. Small amount of sulphur, iron, copper & some vitamins
are present. There are more than 70 enzymes and co-enzymes; these enzymes are
distributed in the matrix and in the membranes.
E) Functions of mitochondria –
The main function of mitochondria is the synthesis of energy rich –
compounds, called ATP, hence mitochondria are also called as “power house of
cells.”
1) Respiratory Centres Only during the aerobic conditions, cells shows presence of mitochondria .
If the cells placed in anaerobic conditions, the mitochondria will disappears , it
clearly shows that the mitochondria are the main respiratory centres.
2) Cell respiration Cell respiration takes place in five steps.
a) Glycolysis – Breakdown of glucose to pyruvate .
It takes place in cytoplasm of cell.
During glycolysis, the net gain of ATP molecules is 2ATP along
with 2 NADH i.e. 6 ATP. Total 8 ATP
b) Oxidative decarboxylation – This is link reaction between glycolysis
Kreb’s cycle .
 Pyruvic acid +CO-A + NAD Acetyl CO-A + NADH2 + CO2
In this process 2 NADH molecules are synthesized i.e. 6 ATP.
c) Kreb’s cycle – The sequence of chemical reactions was firstly
discovered by Sir Hans Kreb (1936) . It is also called citric acid cycle
tricarboxylic acid cycle.
Here ,the pyruvic acid is completely oxidized to CO2 & H2O &
24 ATP molecules are produced.
Total energy yield –
C6H120 6 + 602 + 6H20 +38 ADP + 38 Pi -Respiratory /
enzymes
6C02 + 12H20+38 ATP
i.e. from 1 glucose molecule, 38 ATP molecules are synthesized.
Another two steps in cell respiration includes Electron transport chain
(ETC)-The NADH molecules formed in the Glycolysis & Kreb cycle
enters into the ETC and converted to ATP.
The next step is oxidative phosphorylation.
3) ATP transport –
ATP stored in mitochondria, provides energy, where energy requirement is
high. Due to contraction of mitochondria ,the energy (ATP) is squeezed out from
mitochondria. It result in relaxation of mitochondrial membrane & lowering ATP
concentration.
DNA & HISTONES
The binding of DNA
A) DNA –
DNA is the main genetic constituent of a cell & it carries all the genetic
information in a coded form, from one generation to the next generation.DNA is
located in the nucleus of the cell, hence it is also called nucleic acid. DNA is also
present in cytoplasmic organelles like mitochondria and chloroplast, it forms cell
organelle genome.
The organelle genome diffess from nuclear DNA i.e. nuclear DNA is linear,
double stranded and enclosed by nuclear membrane & present in nucleoplasm.
The cell organelle DNA is circular, not enclosed within envelope & suspended
within matrix.
The DNA consists of – Sugar – Deoxyribose Sugar
Phosphoric acid
Purines & Pyrimidines – Nitrogenous bases
Nucleosides
Nucleotides
Sugar & phosphate forms backbone of DNA by phosphodiester linkage. Purines are
Adenine & Guanine these are double ring compound & pyrimidines are Cytosine,
Thymine & Uracil, these are single ring compound.
The purines always pairs with pyrimidines . The pairing is A=T and C= G
The bonds between nitrogenous bases are hydrogen bonds .
Fig. Watson & Crick double helix of DNA.
B) HistonesHistones are small proteins and are basic in nature, because they have a
content of basic amino acid i.e. Arginine & Lysine. Because of their basic nature,
the histones binds tightly to DNA which is acidic.
There are five different types of histones –
2H1,H2A, H2B, H3, H4.
Out of these five, histone H1 is Lysine rich, which can be easily separated
from DNA in chromosome ( chromatin) indicating that this histone is not tightly
bound to DNA i.e. Histone H1 seals off DNA.
The remaining four main histones H2A, H2B, H3 & H4 are considered as
most conserved proteins, because they exhibit similar nature in different species.
Out of these four, H2A and H2B are slightly Lysine rich and H3 & H4 are
Arginine rich proteins . These four histones are called core histones, and are
present in equimolar amount.
The H1 histone mainly involved in higher order folding of chromatin
while core histones are used for holding together the DNA molecules in chromatin
fibres.
NUCLEOSOME & HIGHER LEVEL OF ORGANIZATION
An average human cell contains about 6.4 billion base pairs of
DNA, divided among 46 chromosomes. Each unreplicated chromosome contains,
a single contineous DNA molecule. The larger the chromosome the longer the
DNA it contains. How it is possible to fit 174 cm of DNA (approximately 2m) in
to a nucleus of only 10 Mm in diameter, and at the same time maintain the DNA
in a state that is accessible to enzymes and regulatory proteins? The answer lie in
the remarkable manner in which a DNA molecule is packaged.
Nucleosome - the lowest level of chromatin organization.
( 10 nm in diameter )
Chromosomes are composed of DNA and associated proteins, which
together is called chromatin. The packaging of eukaryotic DNA depends on
histones , a remarkable group of small proteins that possess high content of basic
amino acids – Arginine & Lysine.
Roger Kornberg (1974) at Harward University proposed entirely new
structure of chromatin. Kornberg proposed that, DNA & histones are organized
into repeating subunits called nucleosome.
Each nucleosome contains a nucleosome core particle consisting of 146
base pairs of supercoiled DNA wrapped almost twice around a disc shaped
complex of 8 histone molecules (2 * H2A H2B, H3 & H4). The remaining histone
type H1 resides outside the nucleosome core particle. The H1 histone is referred to
as linker histone because it binds to part of linker DNA that connect the
nucleosome core particle to the next.
As the each nucleosome consists of 8 subunits of core histones, it is also
called octamer.
Solenoid Model – Second level of chromation organization –
(30 nm. Fibre).
Solenoid is the next level of chromatin organization of the nucleosome.
Maintenance of solenoid structure depends on the interaction between histone
molecules of neighbouring nucleosomes. Linker histones and core histones both
implicated in the formation of solenoid structure.
Solenoid is nothing but, wire coiled around central hollow axis .Each turn is
having 6 nucleosomes. Solenoid is looks like disc shaped rather than spherical.
CELL
The structural & functional unit of life
Cell is a fundamental unit of structure of function in an organism.
Prokaryotic cell
1) Structure of prokaryotic cell.
Eukaryctic cell
1) Structure of eukaryotic cell.
2) Examples -bacterial cells & blue green
algal cells.
2) Examples- cells in all higher animals
& plants
3) Cell size is very small i.e. 1-4 M.
4) Cell wall is non – cellulosic
3) Cell size larger than 5 M.
4) Cellulosic cell wall is present only in
plant cells.
5) Cytoplasm is without endomemb.
5) Cytoplasm is with endomembrane
System , without membrane bound
system & many memb. bound cell
cell
organellies,
no
cytoplasmic
organelles,
cytoplasm
shows
streaming no vacuoles.
streaming movements, vacuoles present.
6) cell organelles.
chloroplast, mitochondria, golgi ER &
cytoskeleton absent.
6) Cell organelles.
Well differentiated chloroplast,
mitochondria,
golgi,
ER
cytoskeleton present.
&
7) Nucleus is not well organized & 7) Nucleus is bounded by nuclear memb.
directly in contact with cyto. Matrix
& well organized.
in contact with cyto. matrix. In the
from of nucloid.
8) Genetic material is circular DNA.
9) Endo & exocytosis absent.
8) Genetic material is linear DNA.
9) Endo & exocytosis present.
NUCLEUS
The heart of cell
1) Introduction –
Nucleus is the membrane bound cell organelle, having the genetic
material and various proteins. On the basis of presence or absence of nucleus, the cells
are of two types i.e. prokaryotic cells & eukaryotic cells. In very cases the nucleus is
absent in cells eg. Human RBCs. Nucleus controls almost all activities of the cells,
hence nucleus controls considered as the brain of the cell.
Generally nucleus is present at the centre of the cell but in some cells it is
eccentric. i.e. towords the base or to words the tip of the cell. According to different
sizes of the cells , nucleus also show variations in shape & size eg. Multilobed
nucleus , oval nucleus, bilobed nucleus, kidney shaped nucleus, C – shaped nucleus
etc.
The nucleus was first detected by Leeuwenhock in 1700. Nuclei were first
discovered & named by Robert Brown in 1833, in plant cells.
2) Ultrastructure –
1) Nuclear membrane ( karyotheca) The nucleus is separated from cytoplasm by a semipermiable
membrane, the nuclear membrane. It is double layer & lipoprotein (lipids
& proteins) in nature, as the same as plasma membrane. The outer layer is
called ectokaryotheca & inner layer is called endo karyotheca .They are
separated by perinuclear space , which is about 150 to 300 A0 .
The nuclear membrane shows nuclear pore. Nuclear pores are
circular in shape.
2) Nucloplasm / Nuclear sap / karyolymph –
The nucleus is filled with a homogenous, transparent, acidophilic .
( stains with acidic stain ) substance known as karyolmph or nucleoplasm.
In the nucleoplasm uncondensed chromatin ( i.e. substance containing
DNA & proteins ) is present . Nucleoplasm contains euchromatin
( contains large amount of DNA) and heterochromatin (less DNA).
Nucleoplasm also contains nucleolus.
3) Chromatin Material Nucleoplasm contains many thread – like , coiled and much
elongated structures, known as the chromatin substance or chromatin
fibres. During the cell division i.e.during mitosis & meiosis the
chromatin material becomes thick, ribbon like known as chromosomes.
Chemically chromatin consists of DNA, RNA, basic proteins
(histores) & non – histone proteins.
4) Nucleolus Nucleoli were described by M. J. Schleiden in 1838. the term
nucleolus was coined by Fontana (1781) & Bowman (1840).
Nucleolus is a spherical ball like body laying in the nucleus. The
nucleolus is present in all nuclei of eukaryotes but absent in certain
type of sperms . The number of nucleoli varies from 1 to 4. The
position of nucleolus within nucleus depends upon chromosomes.
The nucleolus is generally spherical in shape.The position of the
nucleolus in the nucleus is generally
eccentric . Ultrastructure of nucleolus shows fibrillar region, granular
region, Amorphous region & nuclear associated chromatin.
3) Functions of Nucleus –
1) Protection of DNA – Nuclear membrane protects DNA from the action
of cytoplasmic enzymes.
2) Nucleo- cytoplasmic material exchange i.e. from nucleus to cytoplasm
to nucleus.
Eg. Ribonucleoproteins , mRNA etc.
3) Contribution to other cell membrane – Biogenesis of endoplasmic
reticulum, mitochondria etc.
4) Synthesis of mRNA – Nucleoplasm carry out synthesis of mRNA.
5) Storage of genetic material in the form of DNA.
6) Controls vital activities of the cells.
7) Chromatin material of nucleus carry genetic information from one cell
generation to the other.
8) Nucleolus carry out rRNA synthesis.
9) Nucleolus plays significant role in mitosis.
10) Biogenesis of ribosomes is the soul function of nucleolus.
CHROMOSOMES
The bags of genes
1) introduction Chromosomes are filamentals or thread like or rod shaped bodies presence
in the nucleus. They are not visible in the active nucleus due to their high water
content, but are visible during cell division. They carry genes or the hereditary
units
.
The chromosomes ( chroma – colour , soma – body ) are easily stained with
dyes. Most of the chromosomes in a cell are called autosomes. In addition there
are also sex chromosomes or heterosomes .
The chromosomes were named by Waldeyer (1888)
3) shape of chromosomes –
The shape of the chromosome is determined by the position of its
centromere. Depending upon the position of centromere , the chromosomes are of
4 types.
A) Telocentric
The centromere is located
at the end of chromosome
or at the tip of chromosome.
These are very rare chromosomes.
C) Submetacentric
B) Acrocentric
These are rod like chromo.in
which the centromere is
situated near the end of
chromo .one arm is very
small & other is very large
(long).
D) Metacentric
These are L- shaped
chromo having two unequal
arms the centromere is
situated some distance away
from the middle.
These are V- shaped chromo .
in which centromere is
situated exactly at the centre.
The two arms are nearly equal.
4) structure of chromosome –
fig. structure of a typical chromosome.
The typical chromosome has elongated, cylindrical & prominent body
consist of two cromatids & matrix . The chromosome shows following
structures.
1) Chromonemata Each chromosome consists of two symmetrical, spirally coiled
& filamentous structures called the chromatids or also called as the
chromonemata. The coiling of chromonemata may be either plectonemic or
paranemic. The plectonemic coiling can be easily separated. Each
chromonemata consist of a single DNA molecule with associated proteins.
2) Chromomeres During metaphase, each chromosome showing two chromatids & fair
granules in the Centro mere. These granules are called centromeric
chromomeres. In anaphase ,when two chromatids separate ,the chromomeres
also separate. Thus two chromomes are found in each chromatid. It is
presumed that genes are located on chromomeres.
3) Centromere A constricted part of the chromosome, where the arms of chromosome
meet, is called centromere. It is also called the primary constriction or
kinetochore. The position of cerntromere varies in different chromosomes,
which gives shape to the chromosome.
During cell division, the centromere is functional, while the rest of the
chromosome is genetically inactive. Centromere is specialized for the
attachment & the formation of the spindle fibres.
According to number of centromeres, the chromosomes are monocentric,
dicentric or polycentric.
4) Secondary constriction -ll
The arms of the chromosome may show one or more secondary constrictions
ll, other than primary constrictions. These are constant in position for a particular
chromosomes, which helps in the identification of chromosomes.
5) Nucleolar organizers The additional constrictions present on the two homologous chromosomes are
called nucleolar organizers or secondary constriction I .These constrictions are
associated with the formation of nucleolus.
6) Satellites A very short piece of chromosome located beyond the nucleolar organizer is
called satellite. It is spherical or round body. The chromosomes with satellite , are
called SAT chromosomes.In chromosomes usually satellites are single.
( SAT = Sine Acido Thymonucleinico).
7) Telomeres The tips of the chromosomes are called telomeres. They differs in structure
and composition from the rest of the chromosome. They prevents the ends of the
chromo.from sticking together. They are specially modified regions of the
chromosome for attachment to the nuclear envelope.
5) Functions of chromosomes –
1) Control on heredity – The hereditary characters of organism are to be
controlled by the chromosomes.
2) Formation of new species –Shifting of position of euchromatin and
heterochromatin shows genetic & phenotypic effects on the organisms.
It leads to format of new species ( speciation ).
3) Formation of nuclolar material – The heterochromatin helps in the
formation of nucleolar material.
4) Control on the synthetic activities of cell – The chromo. Carries
genes, which controls the synthetic activities of the cell eg. Synthesis
of RNA & proteins .
5) Chromosomes also controls physiology of animals.