Vikasana - CET 2012 · y2) Mitosis –( indirect cell division) ( somatic cell division ) (...
Transcript of Vikasana - CET 2012 · y2) Mitosis –( indirect cell division) ( somatic cell division ) (...
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Cell cycle & cell DivisionCell cycle & cell DivisionCell: cell is the basic structural & functional unit of the li i i living organism
Type of cells:Prokaryotic cell & Prokaryotic cell & Eukaryotic cell
Types of organisms based on number of cell: Types of organisms based on number of cell: unicellular organism & Multi cellular organism Multi cellular organism
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Cell cycle: the series of events Cell cycle: the series of events occurring during the cell formations & cell division
OrOrThe orderly sequence of precise events by which the cell duplicates its contents and 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)/Meiotic) (the dividing part)3) Every time the cell cycle is
completed, the number of cells increases & there by growth is
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increases & there by growth is achieved
Cell division:Cell division:The Process of formation of new cells (daughter cells)from the Pre‐ existing Parent cell is called cell division
Type of cell divisionType of cell divisionBasically there are 3 types of cell division1)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 . 2) Mitosis – ( indirect cell division) ( somatic cell division ) ( equational division ) – mitosis is process of cell division in ( equational division ) mitosis is process of cell division in which chromosomes or duplicated & chromosomes are equally distributed to the newly formed two daughter cells3) Meiosis ( reduction division )‐Meiosis is a Process cell 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 hapoidll f h
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cells form the gametes
Interphase:p1. The cell cycle of a somatic cell ( Reproductive
cell)consists of the most active & non dividing phase called interphase
2 Resting stage but not so but is very active stage 2. 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 –phasephase 2) S phase 3) G2 phase5. In G1 phase – ( post mitotic or meiotic gap phase) 1) Active Synthesis of RNA2)Active Synthesis of required proteins in histones ) &
en mes enzymes 3) cell grows in size 4) nucleus is en larged5) chromosomes or loosely coiled like fibers y6)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
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p p
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 p3) chromosomes double every where except at the centromere. 4) the quantity of the DNA of the cell becomes doubled5) now nucleus appears very prominent and relatively large 5) now nucleus appears very prominent and relatively large with dark contents or the chromosomal fibers In G2‐ phase( Pre –Mitotic gap phase) –
1) further RNA synthesis takes place 1) further RNA synthesis takes place 2) other required proteins are produced 3) spindle fiber Proteins also produced ) f h ll l k l4) further in crease in cell size & volume take place
5) cell organelles & Macro Molecules are formed, energy rich compounds are formed
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InterphasePl C llAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
MITOSIS:(Somatic cell division)MITOSIS:(Somatic cell division)( equational division)
Mitosis is a process of cell division in which chromosomes are duplicated and chromosomes are equally distributed to chromosomes are equally distributed to the newly formed two daughter cells.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:Karyokinesis is the process of the division of nucleus of the parent (mother) cell into two daughter nuclei Karyokinesis can be studied in four stages namely
1)Prophase ) h2) Metaphase 3) Anaphase ) T l h 4) Telophase
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PROPHASE:1. Prophase is the initial stage of the
k ki ikaryokinesis.2. The chromatin network in the nucleus
become shorter & Thicker due to i li ti ( ili ) & d ti spiralization (coiling) & condensation
3. Each thin, long, chromosomal fiber (threads) become thicker & shorter now ll d h called as a chromosome,
4. Each duplicate chromosome has 2 identical threads called, chromosomes, but are still held together at common but are still held together at common centromere (Kinetochore)
5. Chromosome are much more recognizable (distinct) at the end of
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recognizable (distinct) at the end of prophase,
6 P i i b l i i b 6. Protein microtubules start organizing between the pre‐determined poles of the cell form the spindle apparatus. 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 &
l l i d
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nucleoplasm are mixed.
ProphasePl C llAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
METAPHASEMETAPHASE1. Proteinaceous spindle fibres are
compactly established between compactly established between the poles in a cell.
2. There are two kinds of spindle 2. 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.
3. The chromosomes become very hi k & h & l l i ibl
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thick & short. & clearly visible
ll h h ddl4. All chromosomes move at the middle part (equator) of the cells & arranged (lie) at the equatorial plate (metaphase plate) (Movement of equatorial plate (metaphase plate), (Movement of chromosomes is called metakinesis)
5. All the chromosomes are arranged in the form of a gring.
6. The centromeres of the chromosomes lie towards th tthe equator.
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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MetaphasePl C llAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
ANAPHASEANAPHASEAnaphase is the stage where the chromosomes are moving to their
i lg
respective poles.It is the shortest stage.The chromosomal fibres attached to the
f h h llcentromere of each chromosomes, Pull the chromosomes to their respective poles. Aft th ti i t h lAfter the some time interchromosomalfibers lengthen & push the chromosomesIt is clear that at the end of anaphase 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 h h l
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pto the another pole.
AnaphasePl C llAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
TELOPHASE:1. At each pole, there is complete group of
h chromosomes. 2. The chromosomes undergo uncoiling
(decondensation) and become thinner & Th d lik & l d & f Thread like & elongated & form chromatin network.
3. Spindle fibres disappear & astral fibres3 p ppdisappear
4. The Nucleus reappears. 5 The nuclear membrane reappears & 5. The nuclear membrane reappears &
surrounds each group of chromosomes. Hence two nuclei are present in one cell.
6 The process of karyokinesis (Nuclear
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6. The process of karyokinesis (Nuclear division) is over.
TelophasePl C llAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
CYTOKINESIS :
In plant cells cytokinesis takes place by the formation of a cell plate which begins at the interior & extends to 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.
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CYTOKINESIS :In animal cells the process of cytokinesis takes places by the formation of constriction (cleavage furrow) which starts at the equatorial region from the 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 ‐‐ ReviewAnimal Mitosis ReviewInterphase Prophase
Metaphase Anaphase
Telophase Interphase
Plant Mitosis ‐‐ ReviewInterphase Prophase
M t h A hMetaphase Anaphase
Telophase InterphaseTelophase Interphase
SIGNIFICANCE OF MITOSIS1. 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.I h l i h i f h l P f 4. It helps in the regeneration of the lost. Parts of the body, old, decaying & dead tissues.
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SIGNIFICANCE OF MITOSIS5 It helps in replacing worn out cells & tissues & 5. It helps in replacing worn out cells & tissues &
helps in healing of wounds.6. It helps in asexual reproduction in lower 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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cancerous growth.
MITOSIS IN PLANT CELL & ANIMAL CELLMITOSIS IN PLANT CELL & ANIMAL CELL –DIFFERENCES
Plant cell Animal cell 1 Centrioles & centrosome 1 Centrioles & centrosome1. Centrioles & centrosome
absent1. Centrioles & centrosome
are present 2 Astral rays absent 2 Astral rays Present2. Astral rays absent 2. Astral rays Present 3. Cytokinesis is by the cell
plate formation3. Cytokinesis is by the
Constrictionplate formation Constriction. 4. Mitosis occurs mainly in
meristems4. Mitosis occurs in tissues
of the bodymeristems of the body
MEIOSISMeiosis is a reductional cell division takes place in germMeiosis is a reductional cell division takes place in germcells (reproductive cells) during the formation of gametes(sex cells) (No. of Chromosomes brought to half by meiosisdivision) In meiosis Chromosomes number is convertedf di l id i h ll h l id i h f lfrom diploid in mother cell to haploid in each four newlyformed daughter cells.Meiosis is an important type of cell division forming a part& l f h ll l f ll d i i& parcel of the cell cycle of sexually reproducing organisms(plants / animals) .The Cell in which meiosis occurs is called meiocyte.
f ll d lMeiosis is a type of cell division involving two successivedivision in which the nucleus & cytoplasm divide twice butthe Chromosomes duplicate only once, but produces, fourhaploid cells
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haploid cells.
A typical meiotic division consists of two successivedi i i i i I ( d i l di i i /h idivisions as meiosis I (reductional division/heterotypicdivision) & meiosis II (equational division/homeotypicdivision) and these each division have the usual stagesdivision) and these each division have the usual stagesas an – Interphase, Karyokinesis & cytokinesis
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MEIOSIS IMEIOSIS – IIn this first half of meiotic division reduction ofchromosome number from mother cell to daughterchromosome number from mother cell to daughtercells occur.INTER PHASE IIn this stage as in metosic division inter celluaractivities with G1,S G2 stage under go with the
li ti f DNA (G ti t i l ) hi hreplication of DNA (Genetic material ) whichbecome doubledKARYOKINESIS I :KARYOKINESIS I :Division of mother cell nucleus into two nucleiKaryokinesis I involve the stages like Prophase I,
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y g pMetaphase I, Anaphase I & Telophase I.
Prophase I:
Meiotic praophase I is an important unique stage inth ll di i i b i t tthe cell division because some very importantchanges occur in the nuclear material.The meiotic Prophase stage I is divided into theThe meiotic Prophase stage I is divided into thefollowing 5 Substages,‐a) lepto tene 2) Zygotene3) pachytene 4) Diplotene 5) Diakinesis
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L t tLeptotene: The chromosomes in the nuclear are long thin gthread 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 membersIn animal cells the duplicated centrioles with
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aster start moving to the opposite poles.
ZYGOTENEChromosomes become shorter & thicker due to condensation The homologous chromosomes attract their counter part each other shows pairing (closing of a counter part each other shows pairing (closing of a zipper) called Synapsis (paternal & maternal) The pairing occurs by the formation of The pairing occurs by the formation of synaptonemal complexPaired homologous Chromosomes called bivalentEach pair of homologous chromosomes now consist of four chromosomes is called tetrad
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Pairing is very accurate
PACHYTENEPACHYTENE: Synapsis is complete paired homologous chromosomes are one paternal pair with its exact maternal pair opposed with each other maternal pair opposed with each other Bivalents become further Shorter thicker The crossing over occurs between non‐sister h tid f h l hchromatids of homologous chromosomesDuring crossing over part of the chromosomal bites cut & join to the non sister chromatids Hence there is exchange of genetic materials between the two 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 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
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which is responsible for minor variation in the organisms
DIPLOTENE
The Synaptonemal complex degenerate & disappears, y p p g pp ,Paired homologous chromosomes begin to separate except in the regions where charismata have been f dformed Chiasmata now appears like across (x) are clearly visiblevisible
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DiakinesisFurther the chromosomes become thicker & ShorterTerminalization on of chiasmata takes place pThe chromosome are now free from each other Nulear mmbrane & Nucleolus disappears & ppThe spindle apparatus begin to form.In animals cells centrioles duplicates & from the In animals cells centrioles duplicates & from the asters each move to the respective poles.
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METAPHASE I: Still th Ch h b thi k h t & Still the Chromosomes have become thicker shorter & highly condensed. Chromosomes start arranging at the equatorial plate with their exact homologous pairs (paternal & 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 sprinkledHalf of the numbers of chromosomes are at upper side & other half of the chromosomes are arranged
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& other half of the chromosomes are arranged towards lower side of the equatorial plate.
ANAPHASE I: The centromere of each chromosome do not di iddivideeach chromosomes has its sister chromatids held at centromereThe homologous chromosome separate & now move towards the opposite poles with the helps of spindle fibershelps of spindle fibersOut of the total numbers of chromosomes half of the chromosomes are moving to the upper pole & other half are moving to the lower polepole & other half are moving to the lower pole.The chromosome numbers is reduced to halfDuring this movements of chromosomes they
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g yappear V,L,J, I Shaped depending on the position of centromere.
TELOPHASETELOPHASE The chromosomes undergo decondensation & become thin & thread likebecome thin & thread likeSpindle apparatus disappearNuclear members re appearsNuclear members re appearsAt 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:
The cytoplasm at the cell is divided by the formationof phragmoplast & cell plate in plants & result in theof phragmoplast & cell plate in plants & result in theformation of two haploid cellIn animals cells cytoplasm divided by the formationsof constriction & also forms two haploid cells.
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MEIOSIS II: (Second division of meiosis)
Meiosis II division is same as mitotic division except for the fact that there is no once again replication of chromosomes.Meiosis II is an equational division
l h k kMeiosis II involves Interphase II, karyokinesis & Cytokinesis II
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Interphase IIInterphase II
Interphase II coccurs in between meiosis I & Interphase II coccurs in between meiosis I & karyokinesis II is of very short duration with few preprations takes place in the cell p p pNucleus becomes larger nucleolous is distinct karyokinesis IINuclear membrane Present
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KaryokinesisThe nuclei in the two daughter cells which are haploid undergo karyiokinesis II to produce 4 haploid nuclei
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PROPHASE II: Chromosomes become shorter & thicker Nuclear membrane & nucleolus disappeared C t i l d li t d & t t i Centrioles duplicated & start moving towards the opposite pole (horizontal)Spindle fibers begin to formSpindle fibers begin to formEach chromosomes are with two chromatids
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METAPHASE II:
Chromosomes have become still thicker shorter distinctively visibleTh i dl fib h d The spindle fibres are attached to the chromosomes at the region of centomerecentomereChromosomes are arranged in equatorial region
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ANAPHASE IIANAPHASE II:The centromere of each chromosomed ddividesThe sister chromotids become daughterTh d h hThe daughter chromosomes movetowards their opposite poles.The chromosomes during theirThe chromosomes during theirmovements appear V.J.L.I shaped basedon the position of centromere in them.
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TELOPHASE IITELOPHASE II :The daughter chromosomes have reached their respective poles. respective poles. the chromosomes undergo decondensation become thinner & longer like fibresSpindle fibres disappear.In mammal cells aster are disappears Nuclear membrane & nucleolus reappears to form 4 distinct haploid nuclei.
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Cytokinesis II
C t ki i II b i b th th ll l t f ti i Cytokinesis II begins by the the cell plate formation in plantsIn animals cytokinesis II begins with constrictionIn animals cytokinesis II begins with constrictionFinally cytokinesis II results in the formation of four haploid cells from a single diploid parent mother cellp g p p
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Overview of MeiosisOverview of Meiosis
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SIGNIFICANCE OF MEIOSIS : Meiosis ensures the reduction in chromosome Meiosis ensures the reduction in chromosome numbers from diploid (27) in the mother cell to a haploid the in the daughter cellsMeiosis process in responsible for maintaining the same numbers of chromosome of species constants from generation to generationMeiosis brings about the variation in the
l i d i & i population due to crossing over & genetic recombination which is evolutionary significance
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significance
Comparison of Mitosis & MeiosisComparison of Mitosis & Meiosis
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Difference Between Mitosis & MeiosisDifference Between Mitosis & MeiosisMitosis Meiosis
1) It occurs in somatic (body cells) 1) It occurs in reproductive cells) ( y ) ) p
2) It is an equational division 2) It is a reducationals division
3) Two diploid daughter cell are produced
3) Four haploid daughter cells are formed p
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)P h I i f l d ti 6) Prophase is of short durations 6)Prophase I is of long duration
7) synapsis do not occurs 7) synapsis occurs
8)Centromere divided during Anphase 8) Centromere do not divide during A h IAnaphase I
9)
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MITOSIS
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MEIOSIS
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