Cell cycle and its regulation

Question 1

What are the named stages of mitosis?

Answer 1

Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 2

What are the cell cycle phases?

Answer 2

M phase - mitosis

G1 (–>G0), S, G2 phases - interphase

Question 3

How is the cell directed to divide?

Answer 3

Growth factors

Intracellular signalling cascades

Question 4

What are the functions and properties of the G0 phase?

Answer 4

Cell is neither dividing nor preparing to divide
Distinct quiescent stage outside of cell cycle
Post-mitotic
Cell cycle machinery dismantled

Question 5

What are the functions and properties of the G1 phase?

Answer 5

Gap
Decision point
Separation of mother and daughter centrioles
Synthesis of mRNA and histones for DNA synthesis
Cell grows in size
Determines whether cell commits to division or to leaving the cell cycle (G0)

Question 6

What are the functions and properties of the M phase?

Answer 6

Minutes relative to 24hr cell cycle model
Nuclear division
Cell division (cytokinesis)

Question 7

What are the functions and properties of the G2 phase?

Answer 7

Gap
Decision point
G2/M DNA damage checkpoint
Rapid cell growth
Protein synthesis

Question 8

What are the functions and properties of the S phase?

Answer 8

DNA replication
Protein synthesis: initiation of translation, elongation and capacity increased
Replication of organelles (mitochondria, Golgi, etc.)
Mother and daughter centrioles duplicate
Needs to coordinate with replication of mitochondrial DNA

Question 9

What happens in prophase?

Answer 9

Condensation of chromatin into chromosomes
Late - nuclear envelope breaks down
Chromosomes enter cytoplasm
Centrosomes migrate to opposite poles and begin to organise spindle

Question 10

What happens in metaphase?

Answer 10

Chromosomes that have leaked into the cytoplasm following the breakdown of the nuclear envelope, go with their pairs to the centre of the cell

Question 11

What happens in early prometaphase?

Answer 11

Breakdown of nuclear membrane
Spindle formation largely complete
Attachment of chromosomes to spindle via kinetochores

Question 12

What happens in anaphase?

Answer 12

Paired chromatids separate to form 2 daughter chromatids
A:
Cohesin (protein complex holding sister chromatids tightly together) broken down
Microtubules get shorter
Daughter chromatids are pulled towards opposite spindle poles
B:
Daughter chromosomes can also reach opposite poles by pulling apart of spindle poles

Question 13

What happens in telophase?

Answer 13

Daughter chromosomes arrive at centrosome/pole
Nuclear envelope reassembles at each pole
Centrosomes are moved apart
Cells try to revert to their normal size
Condensation of material where cells are going to split
Assembly of contractile ring of actin and myosin filaments
Contractile ring squeezes cell –> divides into 2
Cleavage furrow = where the cells are going to be cleaved

Question 14

What happens in late prometaphase?

Answer 14

Microtubule from opposite pole is captured by sister kinetochore
Chromosomes attached to each pole congress to middle
Chromosome slides rapidly towards centre along microtubules
Specialised proteins in kinetochores sense attachment of microtubules, e.g. CENP-E

Question 15

What happens in cytokinesis?

Answer 15

Last phase of mitosis
Insertion of new membrane at cleavage furrow
Midbody = where actin-myosin ring is formed

Question 16

What effects do internal checkpoints have on the regulation of the cell cycle?

Answer 16

Control timing and coordination of the cell cycle phases to ensure a correct order of events

Question 17

What are the 3 internal checkpoints?

Answer 17

G1/S checkpoint
G2/M checkpoint
Spindle assembly checkpoint

Question 18

When is and what happens at the spindle assembly checkpoint?

Answer 18

When cell wants to exit metaphase and enter anaphase
Senses completion of chromosome alignment
Checks for spindle assembly
Signalling proteins (e.g. CENP-E, BUB protein kinase) on kinetochore stop emitting signal when kinetochore attaches to microtubules
Hopefully all kinetochores stop sending signals so they can proceed to anaphase