Cell Cycle Flashcards by Ishi Datta

Give five reasons as to why different cells divide at different rates

Embryonic vs. Adult
Complexity of system 
Necessity of renewal 
State of differentiation (some cells e.g neurons never divide)
Tumour cells

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Why is it important to regulate cell division?

Abnormal mitosis results in:
cell death
mutations in oncogenes and tumour suppression genes
chromosomal instability (loose/gain whole chromosomes during cell division)
Deviation of protein levels of cell cycle regulators
Contact inhibition of growth
Attack machinery that regulates chromosome segregation

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What is the cell cycle?

Orderly sequence of events in which a cell duplicates its contents and divides in two
simply: duplication, division + co-ordination

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What occurs during the M-phase?

Nuclear division

Cytokinesis (cell division)

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What occurs during interphase?

DNA + organelle replication

Protein synthesis

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Why is mitosis the most vulnerable period of the cell cycle?

Cells are more likely to be killed (irradiation, heat shock, chemicals)
DNA damage cannot be repaired
Gene transcription silenced- no new proteins
Metabolism slows down

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What happen during G0 phase?

Cell cycle machinery dismantled

Functions normally

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What happens during G1 phase?

Decision point- is it able to replicate?

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What happens during S phase?

Synthesis of DNA/Protein

Replication of all the organelles

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What happens during G2 phase?

Another decision point

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What do the centrosomes do?

Consists of two centrioles, barrels of nine triplet microtubules
Microtubules organising centre
Duplicate before entering S phase

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What are the 6 phases of Mitosis?

Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

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What happens during prophase I?

Condensation of chromatin

Strong and packed so the chromosomes can move without too much damage

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What is a condensed chromosome made up of?

2 sister chromatids each with a kinetochore

Attached by centromere

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What happens during prophase II?

Duplicated centrosomes migrate to opposite sides of the nucleus and organise the assembly of spindle microtubules
Mitotic spindle from outside nucleus between the 2 centrosomes

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What is the spindle?

Radial microtubule arrays from around each centrosome
They grow until they meet in the centre
Polar microtubules form

What happens during prometaphase I?

Chromosome aligned at equator of the spindle Breakdown of nuclear envelope
Spindle formation largely complete
Attachment of chromosomes to spindle via kinetochores

What happens during prometaphase II?

Microtubule from opposite pole is captured by sister kinetochore
Chromosomes attached to each pole conger to the middle
Chromosomes slides rapidly towards centre along microtubules

What happens during Anaphase A?

Cohesin, which holds sister chromatids together, breaks down
Microtubules shorten
Daughter chromosomes pulled towards opposite poles

What happens during Anaphase B?

Daughter chromosomes migrate towards poles

Spindle poles migrate apart

What happens during telophase?

Daughter chromosome arrive at spindle
Nuclear envelope reassembles
Assembly of contractile ring that separates the two cells

What happens during cytokinesis?

Ring contracts
Midbody (remnants from microtubules that coordinated migration of chromosomes) begins to form
Cells divide

What happens during the transition out of metaphase?

Spindle assembly checkpoint
Make sure all chromatids are bound to a microtubules
And that the microtubules are from different poles

How does the cell communicate that the checks have been completed?

Each sister chromatid needs to signal

Proteins (CENP-E and BUB protein kinases) dissociate from kinetochore when chromosomes are properly attached.

How may aneuploidy occur?

Mis-attachment of microtubules to kinetochores | Aberrant centrosome/DNA replication (multiple rounds of replication)

What happens of the cell is not big enough or their is DNA damage?

1. Cell cycle arrest - at check points (G1 and spindle check point) - can be temporary (following DNA repair) 2. Programmes apoptosis - DNA damage too great cannot be repaired - Chromosomal abnormalities - Toxic agents

How can tumour cells avoid check points?

Growth factors at G1 checkpoint induces hyper proliferation May block G2 checkpoint, mitosis started when cell is not ready Block Metaphase checkpoint

How else may tumours deregulate cells?

Block exit from cell cycle into G0 phase | Cells repeat cycle immediately

What triggers a cell to enter the cell cycle and divide?

Growth factors

What happens during a signalling cascade?

Réponse to extracellular factors Signal amplification Signal integration Modulation by other pathways

What happens during protein kinase cascades?

Sequence of phosphorylation and activation of subsequent kinases Signal reversed by phosphotases Leads to amplification, diversification and opportunity fro regulation

What dis c-Myc protein do?

Transcription factor Peaks when growth factors are present It is an oncogene- over expressed in many tumour cells

What are cyclin-dependent kinases?

Present in proliferating cells throughout cycle Activity regulated by interaction of cyclins and phophorylation 4 types: 1,2,4+6

What do cyclins do?

4 types: A,B,D+E Transiently expressed at specific points in cell cycle Regulated at level of expression Synthesised then degraded