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Vikasana - CET 2012
Cell cycle & cell Division
Cell cycle & cell Division
y Cell: cell is the basic structural & functional unit of the living organism li
i i Type of cells:
y Prokaryotic cell & y Eukaryotic cell
Types of organisms based on number of cell: y unicellular organism & y Multi cellular organism Vikasana - CET 2012
Cell cycle: the series of events occurring during the cell formations & cell division
Or
y The orderly sequence of precise events by which the cell duplicates its contents and divides into two new cells is called cell cycle Two stages of cell cycle are Two stages of cell cycle are –
1) Inter phase (non dividing part)
2) 2) M‐ phase (mitotic /Meiotic) (the dividing part)
3) Every time the cell cycle is completed, the number of cells increases & there by growth is achieved
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Cell division:
Cell division:
y The Process of formation of new cells (daughter cells)from the Pre‐ existing Parent cell is called cell division Type of cell division
Basically there are 3 types of cell division
y 1)Amitosis (direct cell division)( no phases) – found in prokaryotic organism found in some lower group of prokaryotic organism , found in some lower group of organism such as protozoan's . y 2) Mitosis – ( indirect cell division) ( somatic cell division ) ( equational division ) division ) – mitosis is process of cell division in which chromosomes or duplicated & chromosomes are equally distributed to the newly formed two daughter cells
y 3) Meiosis ( reduction division )
3) Meiosis ( reduction division )‐ Meiosis is a Process cell division takes place in germ cell ( Reproductive cells) during the formation of gametes , in which the parents cell is Producing four new haploid cells & these four hapoid
cells form the gametes ll f
h
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Interphase:
p
The cell cycle of a somatic cell ( Reproductive cell)consists of the most active & non dividing phase called interphase 2
2.
Resting stage but not so but is very active stage Resting stage, but not so , but is very active stage , Metabolically & biosynthetically active 3.
Longest part of the cycle 4.
Interphase is divided into three sub – phases ‐1)G1 –
phase 2) S‐ phase 3) G2 –phase
phase 2) S
phase
5.
In G1 phase – ( post mitotic or meiotic gap phase) 1) Active Synthesis of RNA
2)Active Synthesis of required proteins in histones ) & en mes enzymes 3) cell grows in size 4) nucleus is en larged
5) chromosomes or loosely coiled like fibers y
6)Go – phase – most of matured cells in the body remain in this stage without passing on to the next S – phase 7) some stimulation is needed for the cell to pass from G1 –
phase to S‐phase p
p
1.
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y In S‐ phase ( synthetic phase ) –
1) Replication & duplication of DNA of all chromosomes in the nucleus takes place 2) DNA of the chromosomes becomes accurately replicated y p
3) chromosomes double every where except at the centromere. 4) the quantity of the DNA of the cell becomes doubled
5) now nucleus appears very prominent and relatively large with dark contents or the chromosomal fibers y In G2‐ phase( Pre –Mitotic gap phase) –
1) further RNA synthesis takes place 2) other required proteins are produced 3) spindle fiber Proteins also produced 4) further in crease in cell size & volume take place )f h
ll
l
k l
5) cell organelles & Macro Molecules are formed, energy rich compounds are formed Vikasana - CET 2012
Interphase
Animal Cell
Pl C ll
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
MITOSIS:(Somatic cell division)
MITOSIS:(Somatic
cell division)
( equational division)
y Mitosis is a process of cell division in which chromosomes are duplicated and chromosomes are equally distributed to the newly formed two daughter cells.
y The Process of mitosis , for the sake of The Process of mitosis for the sake of convenience of study, it has been divided into 1) Karyokinesis ( division of the nucleus ) 2) Cyto kinesis ( division of cytoplasm)
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KARYOKINESIS:
y Karyokinesis is the process of the division of nucleus of the parent (mother) cell into two daughter nuclei y Karyokinesis can be studied in four stages namely 1)Prophase 2) Metaphase )
h
3) Anaphase 4) Telophase ) T l h Vikasana - CET 2012
PROPHASE:
Prophase is the initial stage of the k
karyokinesis.
ki i
2. The chromatin network in the nucleus become shorter & Thicker due to spiralization (coiling) & condensation i li ti ( ili ) & d
ti 3. Each thin, long, chromosomal fiber (threads) become thicker & shorter now called as a chromosome, ll d h
4. Each duplicate chromosome has 2 identical threads called, chromosomes, but are still held together at common centromere (Kinetochore)
5. Chromosome are much more recognizable (distinct) at the end of prophase,
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1.
6. Protein microtubules start organizing between 6
P
i i
b l i i b
the pre‐determined poles of the cell form the spindle apparatus. 7. In animal cell, the centriole near the nucleus duplicate & the to centrals asters (radiating set of micro tubules) move away to each other and reach opposite poles. The spindle apparatus organize between to asters organize between to asters. 8. In plants spindle apparatus is organized without involvement of the asters.
9. At the end of prophase nuclear membrane & Nucleolus gradually disappear & cytoplasm & nucleoplasm are mixed.
l
l
i d
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Prophase
Animal Cell
Pl C ll
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
METAPHASE
1.
2.
3.
Proteinaceous spindle fibres are compactly established between the poles in a cell.
There are two kinds of spindle fibres. The fibres which run from pole to pole called continuous fib & th fib hi h fibres. & the fibres which are attached to the kinetochore micro tubules of the centromere, are ,
called chromosomal fibres. The chromosomes become very thick & short. & clearly visible
hi k & h
& l l i ibl
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4. All chromosomes move at the middle part ll h
h
ddl
(equator) of the cells & arranged (lie) at the equatorial plate (metaphase plate) (Movement of equatorial plate (metaphase plate), (Movement of chromosomes is called metakinesis)
g
5. All the chromosomes are arranged in the form of a ring.
6. The centromeres of the chromosomes lie towards th the equator.
t
7. At the end of metaphase the centromere of each chromosomes divides hence each chromatid has chromosomes divides, hence each chromatid has its own centromere
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Metaphase
Animal Cell
Pl C ll
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
y
y
y
y
y
ANAPHASE
Anaphase is the stage where the chromosomes are moving to their g
respective poles.
i l
It is the shortest stage.
The chromosomal fibres attached to the centromere of each chromosomes, Pull f
h h
ll
the chromosomes to their respective poles. Aft th After the some time interchromosomal
ti i t h
l
fibers lengthen & push the chromosomes
It is clear that at the end of anaphase one complete set of chromosomes finally reached to the one pole & other complete set of chromosomes reached p
to the another pole.
h h l
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Anaphase
Animal Cell
Pl C ll
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
TELOPHASE:
1.
2.
33.
4.
5
5.
6
6.
At each pole, there is complete group of chromosomes. h
The chromosomes undergo uncoiling (decondensation) and become thinner & Th d lik & l
Thread like & elongated & form d & f
chromatin network.
Spindle fibres
p
disappear & astral fibres
pp
disappear The Nucleus reappears. The nuclear membrane reappears & surrounds each group of chromosomes. Hence two nuclei are present in one cell. The process of karyokinesis (Nuclear division) is over. Vikasana - CET 2012
Telophase
Animal Cell
Pl C ll
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
CYTOKINESIS :
y In plant cells cytokinesis takes place by the formation of a cell plate which begins at the interior & extends to the exterior. Cell plate is formula form elements of ER & Vesicles of golgi the substance involved in the formation of cell plate is called phragmoplast primary & secondary walls formed on either side & later cell plate become middle lamella plate become middle lamella. Vikasana - CET 2012
CYTOKINESIS :
y In animal cells the process of cytokinesis takes places by the formation of constriction (cleavage furrow) which starts at the equatorial region from the periphery & extends to the interior of the cell, finally deepens to divide the cell into two. p
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Animal Mitosis ‐‐ Review
Animal Mitosis Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis ‐‐ Review
Interphase
Prophase
M t h
Metaphase
A
Anaphase
h
Telophase
Interphase
SIGNIFICANCE OF MITOSIS
Mitosis Maintains constant number of chromosomes in the body cell.
2. qualitative & quantitative distribution of Chromosomes is maintained 3. It is responsible for the growth & development of multicellular organisms.
4. It helps in the regeneration of the lost. Parts of I h l i h i f h l
P
f the body, old, decaying & dead tissues. 1.
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SIGNIFICANCE OF MITOSIS
55. It helps in replacing worn out cells & tissues & It helps in replacing worn out cells & tissues & helps in healing of wounds.
6. It helps in asexual reproduction in lower organisms (binary fission) 7. It helps in maintenance of the nuclear cytoplasm ratio.
8. The zygote (fertilized egg) develops into the adult by the process of mitosis adult by the process of mitosis. 9. Uncontrolled mitotic division can cause cancerous growth.
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MITOSIS IN PLANT CELL & ANIMAL CELL
MITOSIS IN PLANT CELL & ANIMAL CELL –
DIFFERENCES Plant cell
1 Centrioles & centrosome
1.
absent
2 Astral rays absent
2.
3. Cytokinesis is by the cell
plate formation
4. Mitosis occurs mainly in
meristems
Animal cell
1 Centrioles & centrosome
1.
are present
2 Astral rays Present
2.
3. Cytokinesis is by the
Constriction
Constriction.
4. Mitosis occurs in tissues
of the body
MEIOSIS
y Meiosis is a reductional cell division takes place in germ
cells (reproductive cells) during the formation of gametes
(sex cells) (No. of Chromosomes brought to half by meiosis
division) In meiosis Chromosomes number is converted
f
from
di l id in
diploid
i mother
h cell
ll to haploid
h l id in
i each
h four
f
newly
l
formed daughter cells.
y Meiosis is an important type of cell division forming a part
& parcell off the
h cell
ll cycle
l off sexually
ll reproducing
d i organisms
i
(plants / animals) .
y The Cell in which meiosis occurs is called meiocyte.
y Meiosis is a type off cell
ll division
d
involving
l
two successive
division in which the nucleus & cytoplasm divide twice but
the Chromosomes duplicate only once, but produces, four
haploid cells.
cells
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y A typical meiotic division consists of two successive
divisions
di
i i
as meiosis
i i I (reductional
( d i
l division/heterotypic
di i i /h
i
division) & meiosis II (equational division/homeotypic
division) and these each division have the usual stages
as an – Interphase, Karyokinesis & cytokinesis
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MEIOSIS I
MEIOSIS –
y In this first half of meiotic division reduction of
chromosome number from mother cell to daughter
cells occur.
y INTER PHASE I
In this stage as in metosic division inter celluar
activities with G1,S G2 stage under go with the
replication
li ti
off DNA (Genetic
(G
ti material
t i l ) which
hi h
become doubled
y KARYOKINESIS I :
Division of mother cell nucleus into two nuclei
Karyokinesis
y
I involve the stages
g like Prophase
p
I,
Metaphase I, Anaphase I & Telophase I.
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Prophase I: y
y
Meiotic praophase I is an important unique stage in
th cell
the
ll division
di i i
b
because
some very important
i
t t
changes occur in the nuclear material.
The meiotic Prophase stage I is divided into the
following 5 Substages,‐a) lepto tene 2) Zygotene
3) pachytene 4) Diplotene 5) Diakinesis
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L t t
Leptotene: y
y
y
y
y
The chromosomes in the nuclear are long thin g
thread like & contain beaded appearance called chromomeres Nucleus increases in volume Bouquet stage Chromosomes are gathered in cluster at one end of the nucleus Chromosomes are attached close together on the nuclear members
In animal cells the duplicated centrioles with aster start moving to the opposite poles.
h
l
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ZYGOTENE
y Chromosomes become shorter & thicker due to condensation y The homologous chromosomes attract their counter part each other shows pairing (closing of a zipper) called Synapsis (paternal & maternal) y The pairing occurs by the formation of synaptonemal complex
y Paired homologous Chromosomes called bivalent
y Each pair of homologous chromosomes now consist of four chromosomes is called tetrad
y Pairing is very accurate
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PACHYTENE: PACHYTENE
y Synapsis is complete paired homologous y
y
y
y
y
chromosomes are one paternal pair with its exact maternal pair opposed with each other Bivalents become further Shorter thicker The crossing over occurs between non‐sister chromatids of homologous chromosomes
h
tid f h
l
h
During crossing over part of the chromosomal bites cut & join to the non sister chromatids Hence there is exchange of genetic materials between the two non‐sister chromatids Exact spot where the exchange of parts of chromosome takes place is called chiasma This exchanges brings the recombination of genes from paternal to maternal or maternal to paternal which is responsible for minor variation in the organisms Vikasana - CET 2012
DIPLOTENE y The Synaptonemal complex degenerate & disappears, y p
p
g
pp
,
y Paired homologous chromosomes begin to separate except in the regions where charismata have been f
formed d
y Chiasmata now appears like across (x) are clearly visible
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Diakinesis
y Further the chromosomes become thicker & Shorter
y Terminalization on of chiasmata takes place p
y The chromosome are now free from each other y Nulear mmbrane & Nucleolus disappears &
pp
y The spindle apparatus begin to form.
y In animals cells centrioles duplicates & from the asters each move to the respective poles.
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METAPHASE I: y Still the Chromosomes have become thicker shorter & Still th Ch
h b
thi k h t & y
y
y
y
y
y
highly condensed. Chromosomes start arranging at the equatorial plate with their exact homologous pairs (paternal & maternal) Spindle fibres attached by to the centromere of the chromosomes ( chromosomal fiber)
Centromere of each chromosomes is facing the poles 4 arms towards the equator.
Continuous fibres are running from pole to pole.
All chromosome are arranged in the from of ring in the sprinkled
Half of the numbers of chromosomes are at upper side & other half of the chromosomes are arranged towards lower side of the equatorial plate.
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ANAPHASE I: y The centromere of each chromosome do not y
y
y
y
y
divide
di
id
each chromosomes has its sister chromatids held at centromere
The homologous chromosome separate & now move towards the opposite poles with the helps of spindle fibers
Out of the total numbers of chromosomes half of the chromosomes are moving to the upper pole & other half are moving to the lower pole.
pole & other half are moving to the lower pole
The chromosome numbers is reduced to half
During this movements of chromosomes they g
y
appear V,L,J, I Shaped depending on the position of centromere. Vikasana - CET 2012
TELOPHASE TELOPHASE
y The chromosomes undergo decondensation & become thin & thread like
y Spindle apparatus disappear
y Nuclear members re appears
y At the end of telophase I two nuclei are formed in the dividing cell with haploid numbers of chromosomes.
g
p
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CYTOKINESIS I:
y The cytoplasm at the cell is divided by the formation
of phragmoplast & cell plate in plants & result in the
formation of two haploid cell
y In animals cells cytoplasm divided by the formations
of constriction & also forms two haploid cells.
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MEIOSIS II: (Second division of meiosis)
y Meiosis II division is same as mitotic division except for the fact that there is no once again replication of chromosomes.
y Meiosis II is an equational division
y Meiosis II involves Interphase II, karyokinesis & l
h
k
k
Cytokinesis II
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Interphase II
Interphase II y Interphase II coccurs in between meiosis I & karyokinesis II is of very short duration with few p p
preprations takes place in the cell p
y Nucleus becomes larger nucleolous is distinct karyokinesis II
y Nuclear membrane Present
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Karyokinesis
y The nuclei in the two daughter cells which are haploid undergo karyiokinesis II to produce 4 haploid nuclei
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PROPHASE II: y Chromosomes become shorter & thicker y Nuclear membrane & nucleolus disappeared y Centrioles duplicated & start moving C t i l d li t d & t t i towards the opposite pole (horizontal)
y Spindle fibers begin to form
y Each chromosomes are with two chromatids
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METAPHASE II: y Chromosomes have become still thicker shorter distinctively visible
y The spindle fibres are attached to Th i dl fib h d the chromosomes at the region of centomere
y Chromosomes are arranged in equatorial region Vikasana - CET 2012
ANAPHASE II
ANAPHASE II:
y The centromere of each chromosome
divides
d
d
y The sister chromotids become daughter
y The
Th
d
daughter
h
chromosomes
h
move
towards their opposite poles.
y The
chromosomes
during
their
movements appear V.J.L.I shaped based
on the position of centromere in them.
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TELOPHASE II
TELOPHASE II :
y The daughter chromosomes have reached their respective poles. y the chromosomes undergo decondensation become thinner & longer like fibres
y Spindle fibres disappear.
y In mammal cells aster are disappears y Nuclear membrane & nucleolus reappears to form 4 distinct haploid nuclei.
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Cytokinesis II
y Cytokinesis II begins by the the cell plate formation in C t ki i II b i b th th ll l t f
ti i plants
y In animals cytokinesis II begins with constriction
y Finally cytokinesis II results in the formation of four haploid cells from a single diploid parent mother cell
p
g
p
p
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Overview of Meiosis
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SIGNIFICANCE OF MEIOSIS : y
y
y
Meiosis ensures the reduction in chromosome numbers from diploid (27) in the mother cell to a haploid the in the daughter cells
Meiosis process in responsible for maintaining the same numbers of chromosome of species constants from generation to generation
Meiosis brings about the variation in the population due to crossing over & genetic l i d i & i recombination which is evolutionary significance
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Comparison of Mitosis & Meiosis
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Difference Between Mitosis & Meiosis
Difference Between Mitosis & Meiosis
Mitosis
Meiosis
)
(
y
)
1) It occurs in somatic (body cells)
1) It occurs in reproductive cells
)
p
2) It is an equational division 2) It is a reducationals division 3) Two diploid daughter cell are produced
p
3) Four haploid daughter cells are formed 4) Daughter cells are similar
4) Daughters cells are divisions 5) Nuleus & Cytoplasm divide once
5) Nuleus & Cytoplasm divide twice
6) P h i f h t d ti
6) Prophase is of short durations 6)P h I i f l
6)Prophase I is of long duration d ti 7) synapsis do not occurs
7) synapsis occurs
8)Centromere divided during Anphase
8) Centromere do not divide during A
Anaphase I
h I
9)
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MITOSIS
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MEIOSIS
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