Download Importance Of Biochemistry

Chapter No. 2
Biochemistry
It is a branch of biology, which deals with the study of chemical components and
chemical processes in living organisms. Or
The scientific study of chemical substances, process, and reactions, that
occurs in living organism.
Importance Of Biochemistry

A basic knowledge of biochemistry is essential for understanding anatomy
(physical structure of organism) and physiology (study of functioning of living
things), because all of the living structures of an organism have Biochemical
Organization.
For example, Photosynthesis, Respiration, Digestion and Muscle Contraction
can all be described in Biochemical terms.

Chemistry Of Life




All living organism are made up of chemical compounds, which are either
organic or inorganic.
The most important organic compounds in living organisms are carbohydrates,
proteins, lipids and nucleic acids.
The important inorganic compounds are water, carbon dioxide, acids, bases
and salts.
The biochemical compounds of a typical bacterial (prokaryotic) and animal
(eukaryotic) cell are:
Cellular Metabolism And Material Exchange
Chemicals taken in from the environment
Used to make chemicals of living matter
New cellular materials
Used for E. Need
METABOLISM: (Gk; matabole = to throw differently, to Change)
 All the chemical reactions taking place within a cell are collectively called
Metabolism
Anabolism Reaction: (Gk; katabole=throwing up)
Those reactions in which simpler substances are combined to form complex
substances with the help of energy are called anabolic reactions.
Catabolic Reaction: (Gk; Katabole = throwing down)
A metabolic process in which energy is released through the conversion of complex
molecules into simpler ones.
Catabolism (Destructive metabolism)
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LIFE’S MOLECULAR DIVERSITY & PROPERTIES OF CARBON




Carbon is the fundamental element of organic compounds.
Certain special properties give it the central position in the skeleton of life.
It can react with many other elements forming covalent bonds.
When it combines with four other atoms or radicals, the four bonds are
arranged symmetrically in a tetrahedron. (Tetraedron=four sided, hedra=face,
an object with four triangular sides)

Tetrahedron is a very stable configuration; this property combined with
tetravalency of carbon makes it a favourable element for synthesis of
complicated cellular structures.
CARBON BONDING BEHAVIOUR
Carbon atom combines covalently, forming branched or unbranched chains or
ring structures.
 Carbon combines with H, O, N, P and S, forming a variety of organic
compounds.
 Carbon and Hydrogen (C-H bond) is the potential source of chemical energy for
all cellular activities.
 C-O association is glycosidic linkage provides stability to the complex
carbohydrate molecules.
 Carbon combines with nitrogen to from peptide bonds and produce proteins,
which are important due to their diversity (variety) in structure and function.
(Peptide bond= A chemical bond formed when the amino group of one amino acid
condenses with the carboxyl group of another)
IMPORTANCE OF ORGANIC COMPOUNDS
 Large organic molecules (macromolecules) such as cellulose, fats, proteins etc
are insoluble in water hence they form cellular structures.
 Macromolecules act as storage for smaller molecules like glucose that is later
on used as source of energy by the cell.
 Micro molecules, such as glucose, amino acids, fatty acids etc. are either
function as pool of energy or subunits to build macromolecules.
 Certain other unstable molecules that are immediately broken down to release
energy e.g. ATP. Such compounds are instant source of energy for cellular
respiration.

Biochemical reactions
Almost all
e.g. Hydrolysis of Most abundant
reactions of
macromolecules in all organisms
cell occur in
presence of water
(65---89%) e.g.
Human Tissues
Medium of life
20% in bone cells
85% in brain cells
Heat capacity
Solvent properties
Ionization of water
Heat of Vaporization
Protection
LIFE SUPPORTING PROPERTIES OF WATER
Water As Solvent
Solvent = A substance that dissolves another material (solute).
Water is an excellent solvent for polar substances. These include ionic substances like
salts, whose charged particles (ions) dissociate (separate) in water.
 Some non-ionic substances like sugar and simple alcohols, which contain
changed (polar) groups such as (- OH), are dispersed in water.
 Once a substance is in solution its molecules or ions can move about freely,
thus making it more chemically reactive.
 It is because of this property of water that almost all reactions in cells occur in
aqueous media.
 In cells all chemical reactions are catalysed by enzymes, which work in
aqueous environment.
 Non-polar organic molecules, such as fats are insoluble in water and help to
maintain membranes that make compartments in the cells.
High Heat Capacity:
The specific heat capacity of water is the amount of heat, measured in calories
to raise the temperature of 1g water by “1C0 ” (i.e., 150c —160c). It is “1” for water.
 Due to high heat capacity water can absorb much of heat with out
increase in its temperature. The most of energy supplied is used to break
hydrogen bonds that result in relatively small rise in temperature.
Benefits: (Water’s Temperature Stabilizing Effects)
i) Biochemical reactions proceed at more constant rates and are less likely to be
inhibited by extremes of temperature.
ii) Water also provides a very constant external environment for many cells and
organisms.
High Heat of Vaporization:
Water absorbs much heat as it changes form liquid to gas. Heat of vaporization
is expressed as clones absorbed per gram vaporized. The specific heat of vaporization
of water is 574 Kcal/ Kg, which plays an important role in the regulation of heat of
produced by oxidation.
The high heat of vaporization means that a large amount of heat can be lost
with minimal loss of water from the body e.g evaporation of only 2ml out of 1liter of
water, lower the temperature of the remaining 998 ml by 10c
Sweating and
Panting of mammals
The grening of
mouth of source
reptiles in sunshin
IONIZATION OF WATER
The water molecules ionize to from H+ and OH- ions.
Transpiring leaves
H2O
H+ + OHThis reaction is reversible but equilibrium to maintain. At 25 0 c the
concentration of each of H+ and OH- ions in pure water is about 10-7 mol/litre. The H+
and OH- ions affect, and take part in many of the reactions that occur in cells.
PROTECTION
Water is affective lubricant that provides protection against damage resulting
from fiction. For example, tear protect the surface of eye from the rubbing of eyelids.
Water also forms a fluid cushion around organs (lungs, heart etc) that helps to
protect them form trauma.
PROTEIN
PRIMARY STRUCTURE:
The primary structure is the number sequence of amino acids held together by
peptide bonds in a polypeptide chain. The sequence of amino acids of a protein
dictates its biological function. In turn this sequence is strictly controlled by the
sequence of bases in DNA. Substitution of just a single amino acid can cause a major
alteration of the function of protein e.g sickle cell anaemia.
Example:
Insulin
Discover
= F. Sanger (1944-1954)
No. of amino acids = 51
Chains
= 02
SECONDARY STRUCTURE:
The polypeptide chains is protein molecule usually do not lie flat. They usually
coil into a helix or into some other regular configuration.
- Helix
- pleated sheet
- Helix :
It usually takes the form of an extended spiral spring. The structure is
maintained by many hydrogen bands which are formed between adjacent Co and NH
groups. The H atom of NH group of one amino acid is bonded to “O” atom of the Co
- Helix makes
group three amino acids away. X-ray diffraction analysis shows that
one complete turn for every 3.6 amino acids.
H
N-H
R-C-H
C=O
H-N
H-C-R
O=C
N-H
R-C-N
C=O
H-N
N-C-R
O=C
N-H
R-C-H
C=O
N-H
Example: Keratin [entirely
- helical and hence fibrous]
 It is structural protein of hair, wool, nails, Claus, beaks feathers and horns.
 Its hardness and stretch ability vary with degree of cross-linking by disulphide
bridges between neighbouring chains.
 Theoretically all Co and NH groups can participate in H-bonding So
-helix is a very stable structure.
ß-PLEATED SHEET:
This protein comprises a number of adjacent chains which are arranged in parallel
fashion but running in opposite directions to each other. They are joined together by
H-bonds formed between the C=O and NH groups of one chain and NH and C=O
groups of adjacent chains. This is called ß-configuration and the whole structure is
known as a ß-pleated sheet.
O
C
O
N
N
R4
O
N
C
C
C
C
R5
N
N
O
R1
N
O
C
N
C
N
N
R2
O
N
C
C
C
C
N
N
C
N R3 O N R 1
R3 O
N R1
C
N
C
C
C
C
N
C
C
N
O
R2
N
O
R4 N
C O
TERTIARY STRUCTURE:
Usually the polypeptide chain bends and folds extensively forming a precise,
compact, globular shape. This is proteins tertiary conformation and is maintained by
the interaction of three types of bonds i.e.
 Ionic
 Hydrogen
 Disulphide bonds as well as hydrophobic interactions
The latter are quantitatively the most important and occur when protein folds so
as to shield hydrophobic side groups from the aqueous surroundings, at the same
time exposing hydrophilic side chains.
C=O
H-N
Hydrogen bonds
between aminoacids
Hydrogen Bonds
between side chains
O-H
O=C
Disulphide bond formed by
sulpher-containing amino acids
S
S
Ionic bond between charged
groups of polypeptide chains
CO
H3N+
Hydrophobic interaction
of non-polar R-groups
RO
R
QUATERNARY STRUCTURE:
Many highly complex proteins consist of an aggregation of polypeptide chains held
together by hydrophobic interactions and Hydrogen and ionic bonds. Their precise
arrangement is the quaternary structure.
Example: Haemoglobin [auocked out by Kendrew and perutz]
It consists of for separate polypeptide chains of two type’s i.e two
-chains contain
141 amino acids which each ß chain contains 146 amino acids.
Structure
Fibrous
Type
Fibrous
Globulins
Composition
Alobabr
Simple
Function
Conjugated
Nature
Function
Secondary
structure
most Perform
structural
important (little or no tertiary functions in cells and
structure)
organisms e.g.
 Insoluble in water
 Collagen (tendons,
 Physically tough
bone matrix)
 Long parallel polypeptide
 Myosin (in muscles)
cahins cross-linked at
 Silk (spider, rubes)
interuals forming long
 Keratin (hair, horn
fibres or sheets.
and feathers)



Tertiary structure most
important
Polypeptide
chains
tightly folded to form
spherical shape.
Easily soluble to form a
colloidal suspension.





Globulins of blood
serum
(immunology)
Form antibodies.
Form enzymes
Form hormones
Important
in
protoplasm b/c they
hold water and
other
substances
and
serve
to
maintain molecular
organisation.
LEVELS OF PROTEIN STRUCTURE
Level of structure
Primary
Description
Sequence of amino acids
Secondary
Alpha helix and ß-sheet
Tertiary
Folding and twisting
Type of Bond
Covalent (peptide) bond
between amino acids
Hydrogen bond between
amino acids along the
peptide chain
Hydrogen, ionic and
Quaternary
Several polypeptides
covalent (S – S) bonds,
hydrophobic
interactions between R
groups.
Hydrogen, ion bond
between
polypeptide
chains.
CARBOHYDRATES (Hydrated Carbons)
SEVERAL FORMULAS:
C x (H2o) y, where x is whole number from three to many thousands.
DEFINITION:
Chemically, carbohydrates are defined as polyhedron aldihydes or ketenes or
complex substances which on hydrolysis yield plyhydroxy aldalydr or ketene
subunits.
OR
Organic compounds deceived from carbon, hydrogen, and oxygen. They are
important source of food and energy for humans and animals.
EXAMPLES:
i) Cellulose of wood, cotton and paper
ii) Starch preset in cereals, root tubers
iii) Cane sugar and milk sugar etc.
SOURCES:
The sources of carbohydrates are green plants. These are primary produces of
photosynthesis. Other compounds of plants (i-e proteins, lipids etc) are produced from
carbohydrates by various chemical changes.
IMPORTANCE:
Carbohydrates are of great significance because
i) They play both structural and functional roles.
ii) Simple carbohydrates are the main source of energy in cells.
iii) Some carbohydrates are the main constituents of cell walls in plants and
micro-organisms.
CONJUGATED MOLECULES: (Conjugate Latin = to marry)
Carbohydrates in cell combine with proteins and lipids and the resultant
compounds (conjugates compounds) are called glycoprotein and glycolipids
respectively. These molecules are much important because.
i) Glycoproteins and clycolipids, have structural role in the extra cellular matrix
of animals and bacterial cell wall.
ii) Both of those conjugated molecules are components of biological membranes.
CLASSIFICATION OF CARBOHYDRATES
(Carbohydrates also called saccharides that is a Greek word “Sakcharon” meaning
sugar)
Sugars
Monosaccharides
Polysaccharides
(many sugars)
Oligosaccharides
(Few Sugars)
A. PHYSICAL PROPERTIES
i)
They are small
i)
molecules
ii) They are sweet in
taste.
iii) They are readily
soluble in water.
ii)
iv) They are crystalline
in form.
v) They are not
hydrolyzed.
iii)
They are larger
than
monosaccharide but
smaller than
polysaccharides.
They are also sweet
but their sweetness
is less than that of
monosaccharide.
They are less
soluble
iv) They are also
crystalline
v) They are
hydrolyzed and on
hydrolysis 2—10
monosaccharide are
produces.
i)
They are
macromolecules.
ii) They are tasteless.
iii) They are insoluble
iv) They are non
crystalline
v) They are also
hydrolyzed and on
hydrolysis they
yield simple sugars.
B. SYNTHESIS
They are simple sugars
Made by joining 2---10 They are made by
anonosacckocides
joining many molecules
of monosaccharide
C. DIAORAMATIC REPRESENTATION OF STRUCTURE
Glycosidic linkage
D. GENERAL FORMULA
(CH2O)n n=3—7
Usually C12H22O11
(2—10 monosaccharide)
Cx (H2O)
E. CHEMICAL PROPERTIES
All are reducing sugars
Some
are
reducing All polysaccharides are
sugars and some are non-reducing
non reducing
In nature monosaccharide with 3 to 7 carbon atoms are found. They are called trios
(3c), tetroses (4c), pentoses (5c), hexoses (6c) and heptoses (7c)
FORMULA:
Glucose is the most important hexose. It is present in free state in fruits like grapes,
figs and dates.
 Our blood normally contains 0.08% glucose.
 In combined form it is present in disaccharides and polysaceliarides e.g.
 Glucose is naturally produced in green plants by photosynthesis.
Light energy
Chlorphyll
6CO2 + 12H2O
12O6 + 6O2 + 6H2O
Energy is consumed in this process. This energy is provided by sunlight. 717.6 Kcal of
solar energy is required for the synthesis of 10 grams of glucose. This energy is stored
in glucose as chemical energy. During oxidation (respiration) of glucose this energy is
released in the body of organisms and is used in different activities e.g. in animals it
is used for:
i) Growth and repair
ii) Maintenance of body temperature.
SIGNIFICANCE OF MONOSACCHARIDES
TRIOSES: C3H6O3 for example cluceraldelyde, Dihydroxyacetone.
 They are intermediate sin respiration (glycolysis) and photosynthesis (dark
reaction)
TETROSES: C4H8O4
Rare in nature. They occur mainly in bacteria.
PENTOSES: CyH10O5 e.g. ribose, ribulose.
 They are the integral part of nucleic acids i.e, ribose is a constituent of RNA
and deoryribose of DNA.
 They are involved in the synthesis of some co-enynos e.g. NAD and NADP.
 They are involved in the synthesis of AMP, ADP and ATP.
 They play a role in biochemical reactions e.g.
 Ribulose bisphosphate is the CO2 acceptor is photosynthesis.
HEXOSES: C6H12O6 e.g. glucose, fructose, galactose, manose.
 They are immediate source of energy e.g glucose in sugar
 They are used in the synthesis of oligosaccharides.
 They are used for the synthesis of polysaccharides.
SIGNIFICANCE OF OLIGOSACCHARIDES
Most commonly studied are:
Glucose + glucose
= maltose
Glucose + galactose
= lactose (milk sugar)
Glucose + fructose
= sucrose (cane sugar, most abundant in planty,
commercial sugars are sugar cane and sugar beat)
Disacchacide and polysaccharide synthesis formula
IMPORTANCE OF POLYSACCHARIDES
IMPORTANCE OF STARCH:
 It is found in fruits, vegetables, grains, seeds and tubers.
 It is main reserve food material in plants, available for animals.
 It gives many molecules of glucose on hydrolysis.
STARCH TEST:
Starch gives blue colour with iodine.
TYPES:
Amylase have unbranched chain of glucose. It is soluble in hot water.
AMYLOPECTIN:
It has branched chains. It is insoluble in hot or cold water.
IMPORTANCE OF GLYCOGEN
 It is also called Animal Starch. It is chide storage compound of animals.
 It is found in liver and muscles. It is also found in all animal cells.
 It gives glucose on hydrolysis.
TEST:
 It is insoluble in water
 It gives red colour with iodine
IMPORTANCE OF CELLULOSE
It is most abundant carbohydrate in nature.
Cotton and paper are the pure forms of cellulose.
It is the main component of cell walls of plants.
It cannot be digested in human trail. However it plays a role in reabsorption
and propulsion of faces in large intestine.
 It is digested in herbivores due to presence of micro-organisms (bacteria,
yeasts, protozoa). These micro-organisms secret an enzyme called cellulose for
its digestion.
 It yields glucose molecules on hydrolysis.




TEST:
 It is insoluble in water.
 It gives no colour with iodine.
i) Solubility
ii) Iodine test
Starch
Genrally
insoluble
Blue colour
Glycogen
Insoluble
Cellulose
Insoluble
Red colour
No colour
PROTEIN
The word protein is derived from a Greek word proteios meaning “first place”.
Every one of us has tens of thousands of different hinds of proteins each with unique
structure suited fro its function. Proteins are important to the structure of cells and
organisms and participate everything they do. Proteins are made of amino-acids.
An amino-acid can be defined as a molecule containing an amino group
(NH2), a carboxyl group (-COOH2), and a hydrogen atom, all bonded to a central
carbon atom:
R= may be a hydrogen atom as in glycine or CH3 as in alamine or any other group. So
amino-acids mainly differ due to the type or nature of R group.
About 170 types of amino-acids have been found to occur in cells and tissues.
Of these about 25 are constituents of proteins. Most of the proteins are however made
of 20 types of amino-acids.
AMINO ACIDS CAN BE LINKED BY PEPTIDE BONDS
Cells link amino acids together by dehydration synthesis.
The linkage between the hydroxyl group (-OH) of carboxylic group of one amino acid
releases H2O and C-N link to form a bond called Peptide Bond. The resultant
compound gycylolanine has two amino acid subunits and is called a dipeptide. A
dipeptide has an amino group at one end a carbonyl group at the other end of the
molecule. So both reactive parts are again available for further peptide bonds to
produce tripeptide, tetrapeptide and pentapeptides etc. leading to a polypeptide
chains.
Polypeptides range in length from a few monomers to 3000 thousand or even
more in different proteins.
For example insulin has 51 amino acids where as haemoglobin has 574.
LIPIDS (Gr. Lipos = fats)
The lipids heterogonous group of compounds related to fatty acids. They are
insoluble in water but soluble in organic solvents such as ether, alcohol, chloroform
and benzene. Lipids include fats, oils waxes, cholesterol and related compounds.
ACYLGLYCEROLS (triglycerides or neutral lipids)
Acylglycerols can be defied as Esters of fatty acids and alcohol (glycerol).
ESTER:
It is defined a chemical compound produced as a result of chemical reaction of an
alcohol with an acid and a water molecule is released as shown below.
C2H5OH + HOOCCH3
C2H5OCOCN3 + N2O
Alcohol
Acetic acid
an ester
GLYCEROL:
A three carbon alcohol, each of whose carbon bears a hydroxyl group. Glycerol
forms the back bone of a fat molecule.
FATTY ACIDS:
Long hydrocarbon chains ending in a carboxyl (-COOH) group. Three fatty
acids are attached to the glycerol backbone in a fat molecule.
PROPERTIES OF FATTY ACIDS
1. Fatty acids contain even number (4-30) of carbon atoms in straight chains
attached with hydrogen and having an (-COOH) group.
2. They may be salutated with no double bonds or unsaturated with 1---- 6
double bonds.
3. In animals the fatty acids are straight chains while in plants these may be
branched on signed.
4. Solubility of fatty acids in organic solvents increases with increase in number
of carbon atoms e.g. palonitic and (cl6) is much more soluble an organic solvent
than butyric acid.
5. Melting paint also increases with increase in number of carbon atoms. e.g. the
melting point of potmicitic and is 63.10c and of butyric acids -80c.
Formula from book
FATS AND OILS
 Fats containing unsaturated fatty acids are usually liquid at room temperature
and are said to be oils e.g. most of plant fats.
 Fats containing saturated fatty acids are sold at room temperature e.g animal
fats.
SPECIFIC GRAVITY OF FATS AND OILS
Fats and oils are lighter than water and have a specific gravity of about 0.8. They are
not crystalline but can be crystallized under specific conditions.
Q;
What is the drawback of a good with high fat contents?
Ans. Higher fat contents of food causes. Slower movement of faces through the
bowels. The bacteria present in food convert the undigested fats into came
causing compounds.
 Also the cholesterol level rises that results in heart disorders.
PHOSPHOLIPIDS
Phospholipids are derivatives of phosphotidic acid, which are composed of glycerol +
fatty acids + nitrogenous bases.
 Nitrogen Bases e.g. chorine, ethanolamine and saline
OR
 A phospholipid has almost the same molecular structure as a cylglycerol. The
only difference is that a phospholipid has one of its fatty acids replaced by a
phosphate ion (Po4) and an R group.
_______
R- Represents a nitrogen base.
Phospholipids are widespread in bacteria, animal and plant cells and frequently
associated with membranes.
WAXES
Waxes are mixtures of long chain alhanes (C25 = C35) and alcohols, ketenes
and esters of long chain fatty acids.
 They are mainly used as water prefixing material by plants and animals e.g
A. Additional protective layer on cuticle of epidermis of some plant organs
eg. Leaves and fruits.
Waxes are esters of fatty
B. Skin, fur and feathers of animals
acids with long chain
C. Exoskeleton of insects
D. Beeswax is a constituent of the honeyalcohols
comb of bees.
TEREMPOIDS
Terpenoids are very large and important group of compounds which are made
up of simple repeating units called isoperenoid units that contain C5 H8 atoms.
These units by condensation in different ways, gives rise to compounds such as
rubber, carotenoids, steroids, terpenes etc.
NUCLEIC ACIDS (DNA and RNA)
ISOLATION:
Nucleic acids were first isolated in 1870 by F. Mieschoer from the nuclei of pus
cells and states sperms of fish.
REASON FOR NAMING:
Nucleic acids are called “nucleic acid” because of their acidic nature.
DEFINITION:
Nucleic acids are complex substances. They are polymers of units called
nucleotides.
NUCLEOTIDE:
A nucleotide is made up of three subunits:
Nucleoside= Nitrogen bare+sugar
Nucleotide = nitrogen +sugar+phosphorus
i) 5- carbon sugar (monosaccharide)
ii) A nitrogen base
iii) A phosphoric acid
TYPES:
Nucleic acids are of two types i-e. DNA (deoxyribonucleic acids) and RNA
(ribonucleic acids)
OCCURRENCE:
DNA occurs in chromosome, in the nuclei of cells and in much lesser amounts
in mitochondria and chloroplasts. Whereas RNA is present in the nucleolus in the
ribosomes, in the cytosol and in smaller amounts in other parts of cell.
RNA
DNA
Phosphoric Sugar
Nitrogen Phosphoric Sugar
acid
bases
acid
Deoxyribose
Ribose
Purines
(larger)
Pyrimidine
(smaller)
Purines
Adenine
Adenine (A)
Nitrogen
bases
Pyrimidine
Guanine
Guanine (G)
Cytosine
(F-?)
Thyonine
(F-?)
Cytosine
(F-?)
Diagrams= Formation of nucleotide -------- show?
Formula of ATP
List of nucleotides and nucleosides
CHARGAFF’S RULES
1. The amounts of A, T, G and C in DNA varies form species to species.
2. In each species, the amount of A = T and the amount of G = C
The percentage of A + G equal 50%
And percentage of T + C equal 50%
Uracil
(F-?)
FEATURES OF THE DNA MOLECULE
Maurice Wilkins and Rosalind Franklin used the technique of X-ray diffraction
to determinate the structure of DNA. At the same time Watson and Crick published
the model of DNA in 1953 in the Journal Nature. They suggested that DNA molecule
has following characteristics.
i) DNA consists of two plynucleotide chains.
ii) The two strands are coiled round each other in the form of a double helix.
iii) The two strands run in opposite direction i-e Antiparallel, the 3/ end one being
opposite to the 5/ end of the other.
iv) The two strands are held together by hydrogen bonds thymine ( T ) and
Guanine (A) is always paired with cytosine ( c ).
v) There are two hydrogen bonds between A and T ( A = T) and three H-bonds
between G and C (G = C).
vi) Along the axis of the molecule the base pairs are 0.34 nm apart and a complete
turn of the double helix comprise 3.4 nm or 10 base pairs.
(3.4 nm = 34 Angstrom)
5/
Sugar + Phosphate
3/
3.4nm (10 base pairs)
5/
3/
THE AMOUNT OF DNA
The amount of DNA is fixed for a particular species, as it depends upon the number
of chromosomes. The amount of DNA in germ cells (sperms and oxa) is one half to
that of somatic cells (cells of body).
RNA (Ribonucleic Acid)
RNA is a polymer (many parts) of rob nucleotides. The RNA molecules occur as
single strand, which may be folded back on itself, to give double helical
characteristics. There are also four nitrogenous bases in RNA i-e A, G, C and uracil
U.
SYTHESIS:
RNA is synthesized by DNA in a process known as transcription.
Messenger RNA
(mRNA)
Ribosomal RNA
(rRNA)
Transfer RNA
(tRNA)
MESSENGER RNA:
As the name indicates it takes the genetic message (message from DNA) from
the nucleus to the ribosomes to form particular proteins. This is a single-strand
molecule formed on a single strand of DNA by a process known as Transcription. In
the formation of RNA only one strand of DNA molecule is copied. Messenger RNA
carries the genetic information from DNA to ribosomes, where aminoacids are
arranged according to the information in mRNA to form specific protein molecule.
This type of RNA consists of a single strand of Variable length. Its length depends
upon the size of the gene as well as the protein for which it is taking the message. For
example, for a protein molecule of 1,000 amino acids, mRNA will have the length of
3,000 nucleotides.
PERCENTAGE:
mRNA is about 3 to 4% of the total RNA in the cell.
The smallest mRNA molecule is approximately 300 nucleotide units
long
TRANSFER RNA
Each amino acid has its own tRNA molecule which transfer amino acids
present in the ribosome. It acts as an intermediate molecule between the triplet code
of mRNA and the amino acid sequence of the polypeptide chain (protein).
TYPES OF tRNA:
There are more than 20 different tRNA molcecules.
PERCENTAGE:
tRNA comprises about 10-20% of the cellular RNA.
SIZE:
It is the smallest of all RNAs, consisting a chain length of 75 to 90 nucleotides.
RIBOSOMAL RNA
Ribosomal RNA was the first RNA to be identified. It makes approximately
80% of the total RNA of the cell. It is synthesized by genes present on the DNA of
several chromosomes found with in a region of the nucleolus known as the Nucleolus
Organiser. It is found in the cytoplasm where it is associated with protein molecules
which together form the cells organelles known as ribosomes (in ribosomes RNA is
40---50% protein = 50---60%) ribosomes are the sites for protein synthesis where
mRNA and tRNA molecule interact to translate the information from genes into a
specific protein.
COMPARISON OF “DNA” AND “RNA”
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2.
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7.
DNA
It contains pentose sugar known
as deoxyribos (formula)
The
molecule
contains
the
phosphoric acid molecule which
connects various sugars with one
another.
The nitrogen bases are Adenine,
Guanine, cytosine and thymine.
Molecules have four nucleotides
as
deoryadenomice
monophasphate, deoryguanosine
Môn phosphate.
The molecule contains a double
strand helix structure in which
many
nucleotides
remain
arranged in pair,
DNA is a genetic material.
Occurs
in
chromosomes,
nucleoplasm
and mitochondria
etc.
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2.
3.
4.
5.
6.
7.
RNA
It contains pentose sugar called
the ribose (formula)
The
molecule
contains
the
phosphoric acid molecule which
connects various sugars with one
another.
The nitrogen bases are: Adenine,
Guanine, cytosine and uracil.
Molecules have four nucleotides
as adenosine Môn phosphate,
guamosine monophsphate and
uridine monophosphat.
The molecules consist of single
chain of polynucleotides.
RNA is a carrier of genetic
informations and it plays very
significant role in the mechanism
of protein in synthesis.
It mostly occurs in nucleolus,
micleoplams and cytoplasm.