chapter 9 b the cell cycle. cell division: key terms b genome: cell’s genetic information b...
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Chapter 9Chapter 9
The Cell The Cell CycleCycle
Cell Division: Key TermsCell Division: Key Terms Genome: cell’s genetic Genome: cell’s genetic
informationinformation Somatic (body cells) cellsSomatic (body cells) cells Gametes (germ cells): Gametes (germ cells):
sperm and egg cellssperm and egg cells Chromosomes: DNA Chromosomes: DNA
moleculesmolecules Diploid (2n): 2 sets of Diploid (2n): 2 sets of
chromosomes chromosomes Haploid (1n): 1 set of Haploid (1n): 1 set of
chromosomeschromosomes
Cell Division: Key TermsCell Division: Key Terms
Chromatin: DNA-protein Chromatin: DNA-protein complexcomplex
Chromatids: replicated Chromatids: replicated strands of a chromosomestrands of a chromosome
Centromere: narrowing Centromere: narrowing “waist” of sister “waist” of sister chromatidschromatids
Mitosis: nuclear divisionMitosis: nuclear division Cytokinesis: cytoplasm Cytokinesis: cytoplasm
divisiondivision Meiosis: gamete cell Meiosis: gamete cell
divisiondivision
Purpose of cell divisionPurpose of cell division
Multicellular organisms depend on Multicellular organisms depend on cell division forcell division for• Development from a fertilized cellDevelopment from a fertilized cell• GrowthGrowth• RepairRepair
20 µm200 µm
(b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM).
(c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).
The Cell CycleThe Cell Cycle
Interphase (90% Interphase (90% of cycle)of cycle)
G1 phase~ G1 phase~ growthgrowth
S phase~ S phase~ synthesis of DNAsynthesis of DNA
G2 phase~ G2 phase~ preparation for preparation for cell divisioncell division
The Cell CycleThe Cell Cycle
Mitotic phaseMitotic phase Mitosis~ Mitosis~
nuclear nuclear divisiondivision
Cytokinesis~ Cytokinesis~ cytoplasm cytoplasm
divisiondivision
MitosisMitosis
ProphaseProphase PrometaphPrometaph
asease MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase
Mitosis AnimationMitosis Animation
Spindle microtubulesSpindle microtubules
CentrosomeAster
Sisterchromatids
MetaphasePlate
Kinetochores
Overlappingnonkinetochoremicrotubules
Kinetochores microtubules
Centrosome
ChromosomesMicrotubules
1 µm
ProphaseProphase
Chromosomes Chromosomes visiblevisible
Nucleoli disappearNucleoli disappear Sister chromatidsSister chromatids Mitotic spindle Mitotic spindle
formsforms Centrosomes Centrosomes
movemove
PrometaphasePrometaphase
Nuclear Nuclear membrane membrane fragmentsfragments
Spindle Spindle interaction with interaction with chromosomeschromosomes
Kinetochore Kinetochore developsdevelops
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MetaphaseMetaphase
Centrosomes at Centrosomes at opposite polesopposite poles
Centromeres are Centromeres are alignedaligned
Kinetochores of Kinetochores of sister chromatids sister chromatids attached to attached to microtubules microtubules (spindle)(spindle)
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are needed to see this picture.
AnaphaseAnaphase
Paired centromeres Paired centromeres separate; sister separate; sister chromatids chromatids liberatedliberated
Chromosomes move Chromosomes move to opposite polesto opposite poles
Each pole now has a Each pole now has a complete set of complete set of chromosomeschromosomes
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TelophaseTelophase
Daughter nuclei Daughter nuclei formform
Nuclear envelopes Nuclear envelopes reappearreappear
Chromatin Chromatin becomes less becomes less coiledcoiled
Two new nuclei Two new nuclei complete mitosiscomplete mitosis
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CytokinesisCytokinesis
Cytoplasmic Cytoplasmic divisiondivision
Animals~ Animals~ cleavage cleavage furrowfurrow
Cleavage furrow
Contractile ring of microfilaments
Daughter cells
100 µm
(a) Cleavage of an animal cell (SEM)
CytokinesisCytokinesis
In plant cells, In plant cells, during cytokinesisduring cytokinesis• A cell plate formsA cell plate forms
Daughter cells
Vesiclesforming cell plate
Wall of parent cell Cell plateNew cell wall
(b) Cell plate formation in a plant cell (SEM)
Binary FissionBinary Fission
Prokaryotes (bacteria)Prokaryotes (bacteria)• Reproduce by a type of cell division Reproduce by a type of cell division
called binary fissioncalled binary fission
• The bacterial chromosome replicatesThe bacterial chromosome replicates
• The two daughter chromosomes The two daughter chromosomes actively move apartactively move apart
Binary FissionBinary Fission
Origin ofreplication
E. coli cell BacterialChromosome
Cell wall
Plasma Membrane
Two copiesof origin
OriginOrigin
Chromosome replication begins.Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell.
1
Replication continues. One copy ofthe origin is now at each end of the cell.
2
Replication finishes. The plasma membrane grows inward, andnew cell wall is deposited.
3
Two daughter cells result.4
The Evolution of MitosisThe Evolution of Mitosis
Since prokaryotes preceded Since prokaryotes preceded eukaryotes by billions of yearseukaryotes by billions of years• It is likely that mitosis evolved from It is likely that mitosis evolved from
bacterial cell divisionbacterial cell division Certain protistsCertain protists
• Exhibit types of cell division that Exhibit types of cell division that seem intermediate between binary seem intermediate between binary fission and mitosis carried out by fission and mitosis carried out by most eukaryotic cellsmost eukaryotic cells
Cell Cycle RegulationCell Cycle Regulation
Growth factorsGrowth factors Density-Density-
dependent dependent inhibitioninhibition
Anchorage Anchorage dependencedependence
The Cell Cycle Control The Cell Cycle Control SystemSystem
The sequential events of the The sequential events of the cell cyclecell cycle
Control system
G2 checkpoint
M checkpoint
G1 checkpoint
G1
S
G2M
The clock has specific checkpointsThe clock has specific checkpointsWhere the cell cycle stops until a go-Where the cell cycle stops until a go-ahead signal is receivedahead signal is received
G1 checkpoint
G1G1
G0
(a) If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.
(b) If a cell does not receive a go-ahead signal at the G1checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.
The Cell Cycle Clock: Cyclins and The Cell Cycle Clock: Cyclins and
Cyclin-Dependent KinasesCyclin-Dependent Kinases
Two types of regulatory proteins are Two types of regulatory proteins are involved in cell cycle controlinvolved in cell cycle control
Cyclins and cyclin-dependent kinases Cyclins and cyclin-dependent kinases (Cdks)(Cdks)
Loss of Cell Cycle Controls Loss of Cell Cycle Controls in Cancer Cellsin Cancer Cells
Cancer cellsCancer cells• Do not respond normally to the Do not respond normally to the
body’s control mechanismsbody’s control mechanisms• Form tumorsForm tumors
CancerCancer
TransformationTransformation Tumor: benign or malignantTumor: benign or malignant MetastasisMetastasis