Cell Cycle, Cell Division And Its Control

Front 1

Sequence of cell cycle

Back 1

1) G1phase
2) S phase - DNA replication (2N to 4N)
3) G2 phase
4) Mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis

Front 2

What happens in G1 phase?

Back 2

- Growth
- Preparation for DNA synthesis

*Cellular contents except chromosomes are duplicated

Front 3

What happens in G2 phase?

Back 3

- Growth
- Preparation for mitosis

*Cell double checks the duplicated chromosomes for errors

Front 4

What is the G0 phase

Back 4

Phase within G1
-> Cell cycle arrest (Non-dividing, quiescent stem cells)

Front 5

Cell cycle checkpoints

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1) Restriction point (Between G1 and S)
2) G2-M transition
3) Metaphase-Anaphase transition

Front 6

What happens in prophase?

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- Replicated DNA condenses into visible chromosomes
- Nucleoli disappears
- Nuclear envelope breaks down
- Centrioles move to opp. ends -> Form microtubule organising centre
- Microtubules form a radiating array
- Chromosome attach to microtubules by kinetochore

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What happens in Metaphase?

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- Kinetochore microtubules are used to pull chromosome apart.

Front 8

What happens in anaphase?

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- When chromosome have reached the centrosome, the poles separate further by elongation of the polar microtubules.
- Chromatid separation

Front 9

What is cohesin?

Back 9

Holds sister chromatids together.
- By metaphase, it's removed
- At anaphase, securin, an inhibitor of separase is hydrolysed therefore cohesin is hydrolysed by separase

Front 10

Disease associated with cohesin

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Cohesinopathies - Missing chromosome/Extra chromosome in daughter cells
E.g. Roberts syndrome, Cornelia de Lange syndrome, Down syndrome, nondisjunction

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What happens in telophase

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- Uncoiling of chromosome
- Reformation of nuclear envelope around each group of chromosomes
- Contractile ring formed from actin & myosin pinches the cell until it cleaves into 2 daughter cells.
-> Cytokinesis

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How is cell cycle progression controlled?

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By cyclin dependent kinases (Cdks)

Front 13

What are CDKI and its example?

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Cyclin dependent kinase inhibitor (CDKI)
e.g. p16, p21
- Act to block the entry into the cell cycle & G1/S transition

Front 14

What is the role of Retinoblastoma (RB) protein?

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- Prevents cell from entering G1 by inhibiting function of the E2F (Pro-cell cycle progression genes - TFs)
- Released E2F proteins when stimulated by G1-CDK

Front 15

Role of E2F proteins

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Activated mechanisms e.g. S-phase entry (DNA synthesis and chromosome duplication)

Front 16

What happens in retinoblastoma?

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If RB gene mutated, no functional RB protein is made in retinal cells
- E2F proteins free to drive the cell cycle forward therefore overproliferation of retinal cells.

Front 17

Restriction Point

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- At the end of G1
- Controlled mainly by the action of the p16, inhibiting CDK4/6 (cannot interact with cyclin D)

Front 18

G2-M transition

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- Uses an activating phosphatase to remove the inhibitory phosphates to prevent cyclin B/CDK1 complex.
- If DNA damage, this phosphatase is inactivated to prevent cell division.

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Metaphase-Anaphase transition (Spindle checkpoint)

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- Tension of microtubules is sensed
- Initiates entry into anaphase, to check microtubules are ready to pull sister chromatids apart.

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Types of Antimitotics

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- Vinca alkaloids: Prevent formation of microtubules e.g. vincristine
- Taxanes: Prevent microtubule assembly e.g. cyclostreptin

-> Non selective

Front 21

Where does crossing over occur in meiosis?

Back 21

Prophase I, crossing over occurs to produce genetic diversity