The Cell Cycle

1
Chapter 12

• The Cell Cycle

2
Cell Division

• Purpose
• 1 cell ? genetically identical daughter cells
• Genetic material
• Genome
• Chromosomes
• Chromatin
• Cells Somatic and Gametes

3
LE 12-4
0.5 µm
Chromosome duplication (including DNA synthesis)
Centromere
Sister chromatids
Separation of sister chromatids
Centromeres
Sister chromatids
4
Cell Division and Distribution of chromosomes

• Sister chromatids
• Centromeres
• Cell division
• Mitosis
• Cytokinesis
• Chromosome number

5
LE 12-5
INTERPHASE
S (DNA synthesis)
G1
Mitosis
Cytokinesis
G2
MITOTIC (M) PHASE
6
Phases of the Cell Cycle

• Interphase
• G1
• S
• G2
• Mitotic phase
• Mitosis
• Prophase, Prometaphase, Metaphase, Anaphase,
  Telophase
• Cytokinesis

7
Mitotic Spindle

• Mitotic spindle Prophase
• Centrosome
• Centrioles
• Replicates
• Migrates to poles
• Aster
• Kinetochore
• At centromere
• Connection to microtubules

8
LE 12-6aa
Centrosomes (with centriole pairs
Chromatin (duplicated)
Early mitotic spindle
Aster
Kinetochore
Fragments of nuclear envelope
Nonkinetochore microtubules
Centromere
Nucleus
Plasma membrane
Nuclear envelope
Chromosome, consisting of two sister chromatids
Kinetochore microtubule
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Metaphase and On

• Metaphase
• Metaphase plate
• Polar microtubules
• Anaphase
• Proteins holding sister chromatids together
  inactivate
• Chromosomes move to opposite poles
• Motor protein walks them over
• Kinetochore end of microtuble shortens

10
LE 12-8b
Chromosome movement
Kinetochore
Tubulin subunits
Motor protein
Microtubule
Chromosome
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LE 12-6ba
Metaphase plate
Cleavage furrow
Nucleolus forming
Nuclear envelope forming
Centrosome at one spindle pole
Daughter chromosomes
Spindle
12
Cytokinesis

• Animal cells
• Cleavage
• Cleavage furrow contraction of ring due to
  interaction of actin and myosin
• Plant cells
• Cell plate
• Vesicles from Golgi apparatus
• Contains cell wall materials ? cell wall

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LE 12-9a
100 µm
Cleavage furrow
Daughter cells
Contractile ring of microfilaments
Cleavage of an animal cell (SEM)
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LE 12-9b
Vesicles forming cell plate
Wall of parent cell
1 µm
New cell wall
Cell plate
Daughter cells
Cell plate formation in a plant cell (TEM)
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Binary Fission (Step 1)
Cell wall
Origin of replication
Plasma membrane
E. coli cell
Bacterial chromosome
Chromosome replication begins. Soon
thereafter, one copy of the origin moves rapidly
toward the other end of the cell.
Two copies of origin
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Binary Fission (Step 2)
Cell wall
Origin of replication
Plasma membrane
E. coli cell
Bacterial chromosome
Chromosome replication begins. Soon
thereafter, one copy of the origin moves rapidly
toward the other end of the cell.
Two copies of origin
Origin
Origin
Replication continues. One copy of the origin is
now at each end of the cell.
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Binary Fission (Steps 3 and 4)
Cell wall
Origin of replication
Plasma membrane
E. coli cell
Bacterial chromosome
Chromosome replication begins. Soon
thereafter, one copy of the origin moves rapidly
toward the other end of the cell.
Two copies of origin
Origin
Origin
Replication continues. One copy of the origin is
now at each end of the cell.
Replication finishes. The plasma membrane grows
inward, and new cell wall is deposited.
Two daughter cells result.
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Cell Cycle Regulation

• Cell cycle control system molecules
• Checkpoints
• Internal and external signals
• Found in G1, G2, M phase
• Restriction point (G1)
• Cyclins and Kinases
• Cyclin-cdk complex (MPF)
• Activates M phase and other kinases
• Inactivates during anaphase cyclin broken down

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LE 12-16b
G1
Cyclin
S
Cdk
M
Degraded cyclin
G2
accumulation
G2 checkpoint
Cdk
Cyclin is degraded
Cyclin
MPF
Molecular mechanisms that help regulate the cell
cycle
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Stop and Go Signals

• Internal signals
• Kinetochore signals delay anaphase
• External signals Requirements for division
• Essential nutrients
• Growth factors (Ex. PDGF) (p. 204)
• Space density-dependent inhibition
• Anchorage

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LE 11-5_3
EXTRACELLULAR FLUID
CYTOPLASM
Plasma membrane
Reception
Transduction
Response
Receptor
Activation of cellular response
Relay molecules in a signal transduction pathway
Signal molecule
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Loss of Control - Cancer

• Do not exhibit density-dependent inhibition
• Do not stop dividing even with lack of growth
  factors
• Steps
• Transformation
• Benign or Malignant tumor
• Metastasis