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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