Cell DivisionCell Division

Your body is composed of Your body is composed of more than a billion cellsmore than a billion cells

Why must cells divide?Why must cells divide?

They are continually They are continually dying and must dying and must produce new cellsproduce new cells

An identical copy of An identical copy of your hereditary your hereditary information is in information is in the nucleus of the nucleus of each and every each and every body cell called a body cell called a somatic cellsomatic cell dbb.urmc.rochester.edu/.../photo_gallery.

ChromosomesChromosomes

The genetic information or blueprint The genetic information or blueprint that is organized into 46 that is organized into 46 chromosomes (each contains about chromosomes (each contains about one to two thousand genes)one to two thousand genes)

KaryotypeKaryotypeHuman Human

chromosome chromosome number: 46number: 46

KaryotypeKaryotype – order – order of of chromosomes chromosomes from tallest to from tallest to smallest.smallest.

Every time a cell divides it must copy Every time a cell divides it must copy the chromosomesthe chromosomes

Goal of MitosisGoal of Mitosis

is to allow for growth is to allow for growth maintain tissuesmaintain tissues

Baby

Grow to adult

Another way to look at this is like Another way to look at this is like this:this:

Stages of Mitosis is IPMATStages of Mitosis is IPMAT

Mitosis animation: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

InterphaseInterphase Time between divisions – cell spends Time between divisions – cell spends

90% of its life here90% of its life here DNA is copied hereDNA is copied here Typical human cell divides every 24 Typical human cell divides every 24

hourshours

Inside – looks like..Inside – looks like..

Diploid - 3 chromosome pairs,

6 individual chromosomes

Your nucleus initially contained six un-Your nucleus initially contained six un-replicated chromosomes, and now it replicated chromosomes, and now it contains six replicated chromosomes. contains six replicated chromosomes.

The two identical copies of each The two identical copies of each chromosome are calledchromosome are called sister sister chromatidschromatids

They remain attached at a point They remain attached at a point called thecalled the centromere centromere

ProphaseProphase Chromosomes Chromosomes

condense (are condense (are visible)visible)

Sister chromatids Sister chromatids pair up.pair up.

Nuclear Nuclear membrane membrane disappearsdisappears

Pro-metaphase-Start moving to Pro-metaphase-Start moving to sides sides

MetaphaseMetaphase

Paired chromatids Paired chromatids line up in the line up in the middle of cellmiddle of cell

AnaphaseAnaphase

Chromatids are pulled into Chromatids are pulled into the apart. They are dragged the apart. They are dragged through the cytoplasm (V-through the cytoplasm (V-shaped)shaped)

TelophaseTelophase Daughter Daughter

chromosomes chromosomes reach the polesreach the poles

Cells start to Cells start to separateseparate

Nuclear membrane Nuclear membrane re-formsre-forms

Cytokinesis Cytokinesis (Cell Cutting)(Cell Cutting)

The two daughter The two daughter cells separatecells separate

At the end of Mitosis, At the end of Mitosis, each daughter cell each daughter cell has an identical set has an identical set of duplicate of duplicate chromosomeschromosomes

They are called They are called SomatesSomates – – body cellsbody cells

Mitosis StagesMitosis Stages

Mitosis animation Mitosis animation http://www.sumanasihttp://www.sumanasinc.com/webcontent/nc.com/webcontent/animations/content/animations/content/mitosis.htmlmitosis.html

Interphase is subdividedInterphase is subdividedG1 – Gap 1 or growth 1 G1 – Gap 1 or growth 1 cell carries out normal functionscell carries out normal functions

G1 is a period of activity in which cells do most G1 is a period of activity in which cells do most of their growing, increasing in size and of their growing, increasing in size and synthesizing new proteins and organellessynthesizing new proteins and organelles

SS

SynthesisSynthesis

– – DNA is copied to prepare to divideDNA is copied to prepare to divide it synthesizes (to make) a duplicate it synthesizes (to make) a duplicate

set of DNAset of DNA

G2G2

G2 – Gap 2 G2 – Gap 2 is where the organelles and molecules is where the organelles and molecules

required for cell division are produced.required for cell division are produced.

M phase then CytokinesisM phase then Cytokinesis

Mitosis takes about an hour (most Mitosis takes about an hour (most time spent during G1, S and G2 time spent during G1, S and G2 phase) phase)

PMATPMAT

Check pointsCheck points G1 – Checks DNA damage before begins G1 – Checks DNA damage before begins

replication (S phase), if damaged then replication (S phase), if damaged then repaired or self destructs if cannot repair.repaired or self destructs if cannot repair.

G2 – Checks DNA to see if properly G2 – Checks DNA to see if properly copied during S phasecopied during S phase

M – checks to ensure spindle fibers M – checks to ensure spindle fibers attach properly during metaphaseattach properly during metaphase

http://www.cellsalive.com/cell_cycle.htmhttp://www.cellsalive.com/cell_cycle.htm

How does Mitosis lead to How does Mitosis lead to Caner?Caner?

Cancer is basically a disease of mitosisCancer is basically a disease of mitosis

What is happening?What is happening?The normal checkpoints that The normal checkpoints that

regulate mitosis are ignored or regulate mitosis are ignored or overridden by cancer cell.overridden by cancer cell.

How does it occur?How does it occur?

a change in function or a a change in function or a DNA DNA mutationmutation occurs in one of several occurs in one of several genesgenes (proteins) that normally (proteins) that normally function to control growthfunction to control growth

ResultResult

Once these crucial Once these crucial Cell Cycle genesCell Cycle genes start behaving abnormally, cancer start behaving abnormally, cancer cells start to proliferate wildly by cells start to proliferate wildly by repeated, uncontrolled mitosisrepeated, uncontrolled mitosis

Tumor production: Tumor production: http://www.youtube.com/watch?http://www.youtube.com/watch?v=_ZEysIhDsok&feature=relatedv=_ZEysIhDsok&feature=related

Examples:Examples:

(1)(1) p53 protein p53 protein can can senses DNA senses DNA damage and damage and halts progression halts progression of cell cycle. Also of cell cycle. Also known as tumor known as tumor suppressor gene.suppressor gene.

However, p53 is However, p53 is mutated in over mutated in over 50% of all human 50% of all human cancers. cancers.

(1)(1) BRCA 1BRCA 1 genegene, , the "Breast the "Breast Cancer Gene"Cancer Gene" normally repairs normally repairs mutations in PTEN mutations in PTEN gene which gene which suppress tumor suppress tumor formationformation

but if a gene contains but if a gene contains mutations such mutations such that BRCA1 does that BRCA1 does not work properly, not work properly, tumor formation tumor formation can begincan begin

MeiosisMeiosis Cell Division to make Cell Division to make

sex cells sex cells (sperm and eggs)(sperm and eggs)

Chromosome number Chromosome number is halved creating is halved creating these cells these cells ex. 46 ex. 46 23 23

Meiosis animation: Meiosis animation: http://www.sumanasinhttp://www.sumanasinc.com/webcontent/anic.com/webcontent/animations/content/meiomations/content/meiosis.htmlsis.html

Diploid vs. HaploidDiploid vs. HaploidDiploid – two or a pair of Diploid – two or a pair of

chromosomechromosome

Haploid – 1 set of chromosomesHaploid – 1 set of chromosomes

Examples:Examples:

Diploid = 2 Diploid = 2 4488

Haploid = 1 Haploid = 1 2244

YOU TRY: If the diploid YOU TRY: If the diploid chromosome number is 28, chromosome number is 28, what is the haploid number?what is the haploid number?

Stages : Stages : IPMAT IPMAT then then PMAT IIPMAT II

Crossing Over (independent Assortment) - tetrad

Crossing OverCrossing Over

Homologous Homologous chromosomes can chromosomes can swap information, swap information, increasing increasing variability in variability in offspringoffspring

Takes place in Takes place in prophaseprophaseTetrad – set of 4

chromosomes

Homologous ChromosomesHomologous Chromosomes The two versions of each chromosomeThe two versions of each chromosome One from mom, one from dadOne from mom, one from dad

GametesGametesGametes are sex cellsGametes are sex cells

Sperm Sperm

EggEgg

Each are haploid – half the number of Each are haploid – half the number of original set of chromosomesoriginal set of chromosomes

Diploid = 46 Diploid = 46

Haploid = 23Haploid = 23

SpermatogenesisSpermatogenesis Creates four functional sperm cellsCreates four functional sperm cells

OogenesisOogenesis Creates one functional Ovum (egg) Creates one functional Ovum (egg)

and 3 polar bodies and 3 polar bodies

Gametes – sex cellsGametes – sex cells

Products of meiosis in Products of meiosis in males formed in males formed in testes?testes?

A: 4 spermA: 4 sperm

Products of meiosis in Products of meiosis in females formed in females formed in ovaries?ovaries?

A: 1 functional egg A: 1 functional egg (the other 3 cells are (the other 3 cells are not functional and are not functional and are reabsorbed by the reabsorbed by the body?body?

Humans have 46 homologous chromosomes (23 pairs)

Stages of MeiosisStages of MeiosisInterphase:Interphase: same as Mitosis same as Mitosis

Prophase 1: Prophase 1: Same except for Same except for Crossing - over can occur – leads to independent Crossing - over can occur – leads to independent

assortment (life is a box of chocolates)assortment (life is a box of chocolates)

Metaphase 1Metaphase 1: Same except that form a tetrad : Same except that form a tetrad Homologous chromosomes that align at the equatorial Homologous chromosomes that align at the equatorial

plate. plate.

Anaphase 1Anaphase 1: Same except that the Homologous pairs : Same except that the Homologous pairs separate with sister chromatids remaining together. separate with sister chromatids remaining together.

Telophase 1Telophase 1: Same except each daughter contains only : Same except each daughter contains only one chromosome of the homologous pair (not a pair of one chromosome of the homologous pair (not a pair of chromosomse).chromosomse).

Second StageSecond StageProphase 2Prophase 2: same as mitosis : same as mitosis

Metaphase 2Metaphase 2: same as mitosis: same as mitosis

Anaphase 2Anaphase 2: Centromeres divide and sister chromatids : Centromeres divide and sister chromatids migrate separately to each pole. (same as mitosis)migrate separately to each pole. (same as mitosis)

Telophase 2Telophase 2: Four haploid daughter cells instead of two. : Four haploid daughter cells instead of two.

. Daughter cells have half the number of . Daughter cells have half the number of chromosomes found in the original parent cell chromosomes found in the original parent cell and with crossing over, are genetically different.and with crossing over, are genetically different.

Timing in MeiosisTiming in MeiosisWhen do Females produce their eggs?When do Females produce their eggs? Prior to birthPrior to birth

What do Males produce sperm?What do Males produce sperm? Once hit pubertyOnce hit puberty

Helpful saying Helpful saying I don’t use “Mi-Toes-es” for making sperm I don’t use “Mi-Toes-es” for making sperm or eggs!or eggs!

Differences between Mitosis Differences between Mitosis and Meiosisand Meiosis

MitosisMitosis MeiosisMeiosis

IPMATIPMAT IPMAT I & PMAT IIIPMAT I & PMAT II

DiploidDiploid HaploidHaploid

SomateSomate GameteGamete

2 cells2 cells 4 cells4 cells

Non-Disjunction- when chromosomes do not Non-Disjunction- when chromosomes do not separate correctly during meiosis.separate correctly during meiosis.

End up with 47 or 45 in each new cell. End up with 47 or 45 in each new cell.

Example:

Downs Syndrome = Trisomy 21 (3 chromosomes 21)

Turner’s Syndrome = one X and no second sex chromosome

Trisomy 21Trisomy 21