The Cell Cycle and The Cell Cycle and Cellular ReproductionCellular Reproduction

OutlineOutline InterphaseInterphase Mitotic StageMitotic Stage Cell Cycle ControlCell Cycle Control ApoptosisApoptosis MitosisMitosis Mitosis in Animal CellsMitosis in Animal Cells CytokinesisCytokinesis CancerCancer Prokaryotic Cell DivisionProkaryotic Cell Division

Most of the cell cycle is Most of the cell cycle is spent in interphase.spent in interphase.

Interphase has three Interphase has three distinct phases of its distinct phases of its own.own.

InterphaseInterphase

•GG11 - Cell doubles its - Cell doubles its organelles and organelles and accumulates materials accumulates materials needed for DNA synthesis.needed for DNA synthesis.

•SS - DNA replication. - DNA replication.•GG22 - Cell synthesizes - Cell synthesizes proteins necessary for cell proteins necessary for cell division.division.

Mitotic StageMitotic StageCell division stage that Cell division stage that includes mitosis (nuclear includes mitosis (nuclear division) and cytokinesis division) and cytokinesis (cytoplasm division).(cytoplasm division).

Cell CycleCell Cycle

Cell Cycle ControlCell Cycle ControlResearchers have Researchers have

identified an internal signal identified an internal signal protein (protein (cyclincyclin) that ) that increases and decreases increases and decreases as the cell cycle continues.as the cell cycle continues.

Cyclin must be present Cyclin must be present for the cell to proceed for the cell to proceed from the Gfrom the G22 stage to the stage to the M stage and from GM stage and from G11 stage to S stage.stage to S stage.

Allows time for any Allows time for any damage to be repaired.damage to be repaired.

Cell Cycle ControlCell Cycle Control

ApoptosisApoptosis

Often defined as Often defined as programmed cell death.programmed cell death.•Cells routinely harbor Cells routinely harbor enzymes (enzymes (caspasescaspases) ) necessary for apoptosis necessary for apoptosis to occur.to occur.

Apoptosis is ordinarily held Apoptosis is ordinarily held in check by inhibitors, but in check by inhibitors, but can be unleashed by internal can be unleashed by internal or external signals.or external signals.

Mitosis increases and Mitosis increases and apoptosis decreases the apoptosis decreases the number of somatic cells.number of somatic cells.

Apoptosis

MitosisMitosisWhen a eukaryotic cell is When a eukaryotic cell is not undergoing division, not undergoing division, the DNA within the the DNA within the nucleus is a tangled nucleus is a tangled mass of chromatin.mass of chromatin.

•Chromatin condenses into Chromatin condenses into chromosomes.chromosomes.Each species has a Each species has a characteristic number of characteristic number of chromosomes.chromosomes.•Diploid (2n) - Two of each Diploid (2n) - Two of each kind.kind.

•Haploid (1n) - One of Haploid (1n) - One of each kind.each kind.

MitosisMitosisDuring mitosis, a diploid During mitosis, a diploid nucleus divides to nucleus divides to produce diploid daughter produce diploid daughter nuclei.nuclei.•Two identical Two identical chromatids are called chromatids are called sister chromatidssister chromatids..

Sister chromatids are attached Sister chromatids are attached to each other at the centromere.to each other at the centromere.•During nuclear division, sister During nuclear division, sister chromatids separate at the chromatids separate at the centromeres, and each centromeres, and each duplicated chromosome gives duplicated chromosome gives rise to two daughter rise to two daughter chromosomes.chromosomes.

Duplicated ChromosomesDuplicated Chromosomes

Mitosis in Animal CellsMitosis in Animal Cells

Each centromere in an Each centromere in an animal cell contains a animal cell contains a pair of barrel-shaped pair of barrel-shaped organelles (centrioles) organelles (centrioles) and an array of short and an array of short microtubules (aster).microtubules (aster).

Centromeres organize Centromeres organize mitotic spindle, which mitotic spindle, which contains many fibers, contains many fibers, each composed of a each composed of a microtubule bundle.microtubule bundle.

Mitosis in Animal CellsMitosis in Animal CellsProphaseProphase

•Chromatin has condensed.Chromatin has condensed.•Nucleolus disappears.Nucleolus disappears.•Nuclear envelope Nuclear envelope disintegrates.disintegrates.

•Spindle begins to Spindle begins to assemble.assemble.

PrometaphasePrometaphase•Kinetochores develop Kinetochores develop on centromere.on centromere.Attach sister Attach sister chromatids to spindle chromatids to spindle fibers.fibers.

MetaphaseMetaphase•Chromosomes, attached Chromosomes, attached to kinetochore fibers, are to kinetochore fibers, are in alignment at center of in alignment at center of cell.cell.

AnaphaseAnaphase•Sister chromatids split, Sister chromatids split, producing daughter producing daughter chromosomes.chromosomes.Daughter chromosomes Daughter chromosomes are pulled to opposite are pulled to opposite poles.poles.

TelophaseTelophase•Spindle disappears as new Spindle disappears as new nuclear envelopes form around nuclear envelopes form around the daughter chromosomes.the daughter chromosomes.Chromosomes become diffuse Chromosomes become diffuse chromatin again.chromatin again.

Nucleolus appears in each Nucleolus appears in each daughter nucleus.daughter nucleus.

Plant Cell DivisionPlant Cell Division

Meristematic plant Meristematic plant tissue retains the ability tissue retains the ability to divide throughout the to divide throughout the plant’s life.plant’s life.•Found at root and Found at root and shoot tips.shoot tips.

Phases of Mitosis in Plant CellsPhases of Mitosis in Plant Cells

CytokinesisCytokinesisCytokinesis accompanies mitosis in Cytokinesis accompanies mitosis in

MOST cells. MOST cells. Mitosis without Mitosis without cytokinesis results in a cytokinesis results in a multinucleated cell.multinucleated cell.

Begins in anaphase, continues in Begins in anaphase, continues in telophase, but does not reach telophase, but does not reach completion until interphase completion until interphase begins.begins.

CytokinesisCytokinesisAnimal CellsAnimal Cells

•Cleavage furrow, membrane Cleavage furrow, membrane indentation between indentation between daughter nuclei, begins as daughter nuclei, begins as anaphase nears completion.anaphase nears completion.

The cleavage furrow The cleavage furrow deepens when a band of deepens when a band of actin filaments actin filaments (contractile ring) forms a (contractile ring) forms a circular constriction circular constriction between the two between the two daughter cells.daughter cells.

Cytokinesis in Animal CellsCytokinesis in Animal Cells

CytokinesisCytokinesis

Plant CellsPlant Cells•Rigid cell wall Rigid cell wall surrounding plant cells surrounding plant cells does not permit does not permit cytokinesis by cytokinesis by furrowing.furrowing.

Cytokinesis begins with Cytokinesis begins with formation of a cell plate formation of a cell plate which eventually which eventually becomes new plasma becomes new plasma membrane between the membrane between the daughter cells.daughter cells.

Cytokinesis in Plant CellsCytokinesis in Plant Cells

The Cell Cycle and CancerThe Cell Cycle and CancerCancerCancer is a growth disorder is a growth disorder that results from the mutation that results from the mutation of genes regulating the cell of genes regulating the cell cycle.cycle.•CarcinogenesisCarcinogenesis, development , development of cancer, tends to be gradual. of cancer, tends to be gradual.

Characteristics of Characteristics of Cancer CellsCancer Cells

Lack differentiation.Lack differentiation.Have abnormal nuclei.Have abnormal nuclei.Form tumors.Form tumors.

•Loss of contact inhibition.Loss of contact inhibition.

Undergo metastasis.Undergo metastasis.•New tumors distant New tumors distant from primary tumor.from primary tumor.

Undergo angiogenesis.Undergo angiogenesis.•Formation of new blood Formation of new blood vessels.vessels.

Origin of CancerOrigin of CancerMutations in DNA repair Mutations in DNA repair mechanisms.mechanisms.

Mutations to proto-oncogenes Mutations to proto-oncogenes and tumor-suppressor genes.and tumor-suppressor genes.•Proto-oncogenes become Proto-oncogenes become oncogenes.oncogenes.

Telomerase allows Telomerase allows cancer cells to cancer cells to continually divide.continually divide.

Prokaryotic Cell DivisionProkaryotic Cell Division

Asexual Reproduction - Asexual Reproduction - offspring are genetically offspring are genetically identical to the parent.identical to the parent.

•Binary fissionBinary fission produces two produces two (binary) daughter cells that (binary) daughter cells that are identical to the original are identical to the original parent.parent.Prokaryotes contain a Prokaryotes contain a single chromosome with single chromosome with only a few proteins.only a few proteins.

Binary FissionBinary Fission

ReviewReview InterphaseInterphase Mitotic StageMitotic Stage Cell Cycle ControlCell Cycle Control ApoptosisApoptosis MitosisMitosis Mitosis in Animal CellsMitosis in Animal Cells CytokinesisCytokinesis CancerCancer Prokaryotic Cell DivisionProkaryotic Cell Division