How would you describe the How would you describe the process by which a multicellular process by which a multicellular

organism increases its size?organism increases its size?

Why do cells stay small?Why do cells stay small?

Cell Growth and Division

ObjectivesObjectives

Explain the problems that growth causes Explain the problems that growth causes for cells.for cells.

Describe how cell division solves the Describe how cell division solves the problems of cell growth.problems of cell growth.

Limits to Cell GrowthLimits to Cell Growth

The The largerlarger a cell becomes, the more a cell becomes, the more demandsdemands the cell places on its the cell places on its DNADNA and and the more the more troubletrouble the cell has the cell has movingmoving enough nutrients and wastes across the enough nutrients and wastes across the cellcell membranemembrane..Two reasons why cell size is limited:Two reasons why cell size is limited:– If a cell were to grow without control, If a cell were to grow without control,

DNADNA overloadoverload would occur. would occur.– Rate of material Rate of material exchangeexchange is dependent is dependent

on on surfacesurface areaareahttp://www.youtube.com/watch?v=xuG4ZZ1GbzI

Exchanging MaterialsExchanging Materials

Food, oxygen and Food, oxygen and water enter the cell water enter the cell through the through the cellcell membranemembrane. Waste . Waste products leave the products leave the samesame way. way.

The The raterate at which this at which this exchangeexchange takes place takes place depends on depends on surfacesurface areaarea (the total area of (the total area of its cell membrane)its cell membrane)

Ratio of surface area to volumeRatio of surface area to volume

As the As the lengthlength of a cell increases, its of a cell increases, its volumevolume increases faster than its surface increases faster than its surface area. area.

The resulting The resulting decreasedecrease in the cell’s in the cell’s surface-area-to-volume ratio makes it surface-area-to-volume ratio makes it more more difficultdifficult for the cell to move needed for the cell to move needed materials materials inin and waste products and waste products outout..

Cell DivisionCell Division

Before a cell Before a cell becomes too becomes too large, it divides large, it divides into two into two daughterdaughter cellscells by a by a process called process called cellcell divisiondivision..

What are Chromosomes?What are Chromosomes?

ChromosomesChromosomes are are made up of made up of DNADNA

DNA carries the cell’s DNA carries the cell’s geneticgenetic codecode

The cells of every The cells of every organism have a organism have a specificspecific numbernumber of of chromosomes.chromosomes.

Uncoiled DNAUncoiled DNA

DNA Coils into ChromosomesDNA Coils into Chromosomes

The structure of a chromosomeThe structure of a chromosome

ChromatinChromatinChromatid Chromatid CentromereCentromereChromosomes are Chromosomes are notnot visiblevisible in most cells in most cells exceptexcept during during cellcell divisiondivision..At the beginning of cell division the At the beginning of cell division the chromosomes chromosomes condensecondense into compact, into compact, visible structures that can be seen under a visible structures that can be seen under a light microscope.light microscope.

The ChromosomeThe Chromosome

ChromosomeChromosome:: “ “X” shaped cell X” shaped cell structure that directs cell activities structure that directs cell activities and passes on and passes on traitstraits to new cells. to new cells.

Each Each identicalidentical strand of the strand of the chromosome is called a chromosome is called a chromatidchromatid..

The strands are The strands are heldheld togethertogether by a by a structure called the structure called the centromerecentromere..

ChromatinChromatin: Loosely : Loosely coiledcoiled DNA DNA

Parts of a ChromosomeParts of a Chromosome

The Cell CycleThe Cell Cycle

InterphaseInterphase– GG11 Phase: Cell Phase: Cell GrowthGrowth

– SS Phase: DNA Phase: DNA ReplicationReplication

– GG22 Phase: Phase: PreparationPreparation for Mitosis for Mitosis

ProphaseProphase

MetaphaseMetaphase

AnaphaseAnaphase

TelophaseTelophase

CytokinesisCytokinesis

The PhasesThe Phases

1.1. IInterphasenterphase

2.2. PProphaserophase

3.3. MMetaphaseetaphase

4.4. AAnaphasenaphase

5.5. TTelophaseelophase

6.6. CCytokinesisytokinesis

LinksLinks

http://www.cellsalive.com/mitosis.htm

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

Interphase: G1Interphase: G1

Cell Cell GrowsGrows

SynthesisSynthesis of of proteinsproteins and new organellesand new organelles

S-PhaseS-Phase

ChromosomesChromosomes are are duplicatedduplicated and the and the synthesis of DNA synthesis of DNA molecules takes molecules takes place.place.

G2 PhaseG2 Phase

Many of the Many of the organellesorganelles and and moleculesmolecules required required for cell division are for cell division are producedproduced..

The cell is then ready The cell is then ready to enter to enter M-PhaseM-Phase to to beginbegin the process of the process of Cell divisionCell division

ProphaseProphase

The chromatin The chromatin condense into condense into chromosomes.chromosomes.

The The centriolescentrioles separate and a separate and a spindlespindle begins to begins to form.form.

The nuclear The nuclear membrane breaks membrane breaks down.down.

MetaphaseMetaphase

The chromosomes The chromosomes lineline up along the up along the middlemiddle of of the the cellcell..

““M”eet in the M”eet in the “M”iddle!“M”iddle!Each chromosome is Each chromosome is connected to a connected to a spindlespindle fiber at its fiber at its centromerecentromere. .

AnaphaseAnaphase

The The sistersister chromatids chromatids separateseparate into into individual individual chromosomes and chromosomes and move move apartapart..

Anaphase Anaphase pulled Apartpulled Apart

TelophaseTelophaseThe chromosomes The chromosomes gather at gather at oppositeopposite ends of the cell and ends of the cell and loselose their distinct their distinct shapesshapes..

TwoTwo new new nuclearnuclear membranes formmembranes form

Two new Nuclei Two new Nuclei

CytokinesisCytokinesis

The cell membrane The cell membrane pinchespinches the the cytoplasmcytoplasm in in halfhalf..Each Each daughterdaughter cell has cell has an an identicalidentical set of set of duplicate duplicate chromosomeschromosomes..

Plant CellsPlant Cells

Plant cells have a cell Plant cells have a cell plateplate that forms that forms betweenbetween the two cells. the two cells.

The The cellcell wallwall is too is too rigid to be pinched rigid to be pinched apart.apart.

Length of the Cell Cycle of a Length of the Cell Cycle of a Human Liver CellHuman Liver Cell

Interphase: 21 hoursInterphase: 21 hoursGrowth : 9 hoursGrowth : 9 hoursDNA Replication: 10 hoursDNA Replication: 10 hoursPreparation for Division: 2 hoursPreparation for Division: 2 hours

Mitosis: 1 hourMitosis: 1 hourProphaseProphaseMetaphaseMetaphaseAnaphaseAnaphaseTelophaseTelophase

Uncontrolled Cell GrowthUncontrolled Cell Growth

Cancer-Cancer- a disorder in which some of the a disorder in which some of the body’s own cells body’s own cells loselose the the abilityability to control to control growthgrowth. .

Disease of the cell cycleDisease of the cell cycle

Summary Video