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Lectures 21 & 22: Mitosis and Meiosis (Cell Cycle Checkpoints (M to G1…
Lectures 21 & 22: Mitosis and Meiosis
M phase & Interphase
M phase (Mitosis & Cytokinesis)
G0 phase (Cells not actively dividing)
G1 phase
S phase (DNA synthesis)
G2 phase (Gap 2)
More proteins produced
Produces sister chromatids
mRNA and proteins synthesized
Constriction mediated by proteins similar to actin and tubulin
Mitosis
Prophase
: Chromosomes condense; spindle forms
Prometaphase
: Nuclear membrane breaks, chromosomes move
Metaphase
: Chromosomes align in middle of cell
Anaphase
: Chromosomes separate, move to opposite ends
Telophase
: Nuclear membrane reforms, spindle breaks down, chromosomes spread out
Cytokinesis
Contractile ring splits one cell into two daughter cells (Cell plate in plants)
Meiosis
Prophase I:
Same as mitosis prophase + Homologous chromosomes pair up
Metaphase I
: Chromosomes line up (independent assortment)
Anaphase I
: Chromosomes pulled apart
Telophase I
: Nuclear envelope forms
Prophase II
: Nuclear Envelope breaks down, spindle forms
Metaphase II
: Chromosomes line up in middle
Anaphase II
: Sister chromatids pulled apart
Telophase II
: Envelope forms, contractile ring
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Factors like Maturation Promoting Factor (MPF) promote different stages in cell cycle
Cyclin: binds to cyclin-dependent kinase (CDK) to form MPF and cause mitosis
There are different types of cyclin-cdk complexes for different stages
Cell Cycle Checkpoints
M to G1 (Metaphase to anaphase)
Blocks anaphase until chromosomes are attached to spindles at kinetochore
DNA Damage checkpoint
Multiple stages; DNA damage activates p53, which promotes transcription of genes that stop & repair
G2 to M (DNA replication checkpoint, cell size checkpoint)
Ensures DNA is completely replicated & cell is big enough
G1 to S (Start, or restriction point)
Point of no return for mitosis; growth factors, cell size, nutrients
Crossing over occurs