Cell Growth and Cell Growth and DivisionDivision

Why do cells divide?Why do cells divide?

DNA “Overload”DNA “Overload”– Not enough information for a big cellNot enough information for a big cell

Exchanging MaterialsExchanging Materials– Must be able to obtain nutrients and Must be able to obtain nutrients and

eliminate wastes easilyeliminate wastes easily Ratio of Surface Area to VolumeRatio of Surface Area to Volume

– Volume increases faster than the Volume increases faster than the surface areasurface area

Surface Area vs. Surface Area vs. VolumeVolume

ChromosomesChromosomes

DNA and proteinsDNA and proteins Each chromosome Each chromosome

consists of two consists of two identical identical sister sister chromatidschromatids

CentromeresCentromeres – – area where the area where the chromatids are chromatids are attachedattached

The Cell CycleThe Cell Cycle

Series of events that cells go through as they Series of events that cells go through as they grow and dividegrow and divide

4 phases4 phases– M phase (mitosis and cytokinesis) – the division of M phase (mitosis and cytokinesis) – the division of

the nucleus and the cellthe nucleus and the cell

– GG11 phase (the first “gap”) – cells increase in size phase (the first “gap”) – cells increase in size and synthesize new proteins and organellesand synthesize new proteins and organelles

– S phase (synthesis of DNA) – the chromosomes are S phase (synthesis of DNA) – the chromosomes are replicatedreplicated

– GG22 phase (the second “gap”) – many of the phase (the second “gap”) – many of the organelles and molecules needed for mitosis are organelles and molecules needed for mitosis are producedproduced

The Cell CycleThe Cell Cycle

The Cell CycleThe Cell Cycle

InterphaseInterphase – G – G11 + S + G + S + G22

M phaseM phase– ProphaseProphase– MetaphaseMetaphase– AnaphaseAnaphase– TelophaseTelophase– CytokinesisCytokinesis

Mitosis

InterphaseInterphase

Cell spends most Cell spends most of its time in of its time in interphaseinterphase

Cell growsCell grows Carrying out basic Carrying out basic

cell functionscell functions Making organellesMaking organelles Copying Copying

chromosomeschromosomes

ProphaseProphase

Nucleoli disappearNucleoli disappear Chromatin condenses Chromatin condenses

(becomes shorter & (becomes shorter & thicker)thicker)

Chromosomes become Chromosomes become visiblevisible

CentriolesCentrioles separate & separate & move to opposite move to opposite polespoles

Spindle fibersSpindle fibers form form between the centriolesbetween the centrioles

Nuclear membrane Nuclear membrane disappearsdisappears

MetaphaseMetaphase

Chromosomes Chromosomes attach to the attach to the spindle fibers at spindle fibers at the centromerethe centromere

Chromosomes Chromosomes align at the align at the equatorequator

AnaphaseAnaphase

Centromeres split Centromeres split apartapart

Chromatids Chromatids separate & move separate & move apartapart

Sister chromatids Sister chromatids are pulled to are pulled to opposite polesopposite poles

TelophaseTelophase

Cell membrane Cell membrane pinches together pinches together at the equatorat the equator

Nucleoli reappearNucleoli reappear Nuclear Nuclear

membrane membrane encloses each set encloses each set of chromosomesof chromosomes

Chromosomes Chromosomes loosen uploosen up

CytokinesisCytokinesis

Division of the Division of the cytoplasmcytoplasm

Begins during Begins during telophasetelophase

Cell membrane Cell membrane continues pinching continues pinching until it separates until it separates forming 2 daughter forming 2 daughter cellscells

Plant cells have a Plant cells have a cell plate that formscell plate that forms

Videos…Videos…

Life Spans of Human Life Spans of Human CellsCells

Controls on Cell Controls on Cell DivisionDivision Cell-to-cell contact – when cells Cell-to-cell contact – when cells

come in contact with other cells, come in contact with other cells, they stop dividingthey stop dividing

Cell Cycle RegulatorsCell Cycle Regulators

CyclinCyclin – a protein which regulates the – a protein which regulates the cell cyclecell cycle– Cyclins bind to enzymes called cyclin-Cyclins bind to enzymes called cyclin-

dependent kinasesdependent kinases– Different cyclin/CDK combinations control Different cyclin/CDK combinations control

different activities throughout the cycledifferent activities throughout the cycle Quality control checkpoints occur Quality control checkpoints occur

throughout the cyclethroughout the cycle– If something goes wrong the cycle stopsIf something goes wrong the cycle stops

Cell Cycle RegulationCell Cycle Regulation

Cell Cycle RegulatorsCell Cycle Regulators

Internal regulators – proteins that Internal regulators – proteins that respond to events inside the cellrespond to events inside the cell– Part of the checkpoint processPart of the checkpoint process

External regulators – proteins that External regulators – proteins that respond to events outside the cell respond to events outside the cell (e.g. growth factors)(e.g. growth factors)– Direct cells to speed up or slow Direct cells to speed up or slow

down the cell cycledown the cell cycle

Uncontrolled Cell Uncontrolled Cell GrowthGrowth CancerCancer – uncontrolled cell growth – uncontrolled cell growth

– Cells no longer respond to the control Cells no longer respond to the control mechanismsmechanisms

– Occurs due to mutations in the DNAOccurs due to mutations in the DNA– Cancer cells crowd out normal cells, Cancer cells crowd out normal cells,

resulting in loss of tissue functionresulting in loss of tissue function Tumor – cluster of cancer cellsTumor – cluster of cancer cells Carcinogens – cancer causing Carcinogens – cancer causing

substancessubstances

CancerCancer

ApoptosisApoptosis

Programmed cell deathProgrammed cell death Occurs when:Occurs when:

– Webbing between human fingers Webbing between human fingers and toes disappears before birthand toes disappears before birth

– Leaves fall from treesLeaves fall from trees Also occurs in cells with DNA Also occurs in cells with DNA

damage to prevent cancerous damage to prevent cancerous growthsgrowths

Stem CellsStem Cells

Unspecialized cells that can become Unspecialized cells that can become specialized under certain conditionsspecialized under certain conditions

Embryonic stem cells – unspecialized Embryonic stem cells – unspecialized cells from an embryocells from an embryo– Can develop into a wide variety of Can develop into a wide variety of

specialized cellsspecialized cells Adult stem cells – found in certain types Adult stem cells – found in certain types

of tissuesof tissues– MightMight be able to develop into different types be able to develop into different types

of cellsof cells