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Question 1

What are the 4 stages of the cell cycle?

Answer 1

G1 phase
S phase
G2 phase
M phase

Question 2

What does “G” mean?

Answer 2

Gap

Question 3

What happens in s phase?

Answer 3

The cell replicates DNA once and only once

Question 4

What happens in M phase?

Answer 4

The cell separates the chromosomes an segregates them equally

Question 5

What are the key events of the M phase?

Answer 5

Nuclear breakdown
Chromosome condensation
Creation of the mitotic spindle
Ordered movement of chromosomes

Question 6

What is kinetochore?

Answer 6

Specialised complex of proteins where spindle MT attach to chromosomes

Question 7

What are asters?

Answer 7

Important in binding the microtubules that bind the chromosome and will stabilise the cell

Question 8

What happens in cytokinesis/

Answer 8

Creation of two new cells
Partitioning of the two nuclei and organelles
Usually symmetrical division
(Stem cells divide asymmetrically)

Question 9

What are the two molecules that are involved in cell regulation at the two check points?

Answer 9

Cyclin

Cyclin - dependent kinase (Cdk)

Question 10

What are the 4 key concepts of Cdks?

Answer 10

Cyclical activation and inactivation of this family of enzymes controls the cell cycle
These enzymes are kinases that are regulated by a subunit called a cyclin whose levels vary
Control of degradation of these regulatory subunits is very important
CDKs phosphorylate proteins that are involved in key cell cycle events - both structural and functional

Question 11

What regulates the activity of CDKs?

Answer 11

Phosphorylation and dephosphorylation

Question 12

What does the enzyme phosphatease do?

Answer 12

Takes away the inhibitory phosphate

Question 13

What does ubiquitin do?

Answer 13

Adding ubiquitin to proteins targets those proteins for rapid degradation

Question 14

What are the 3 types of cyclin and what do they do?

Answer 14

S cyclins
Activate CDKs just prior to S phase

M cyclins
Activate CDKs and regulate entry into mitosis

G1/S cyclins
Activate CDKs in late G1

Question 15

What conditions in G1 would not allow the cell cycle to continue?

Answer 15

Damaged DNA

Unfavourable extracellular environment

Question 16

What conditions in S would not allow the cell cycle to continue?

Answer 16

Damaged or incompletely replicated DNA

Question 17

What conditions in G2 would not allow the cell cycle to continue?

Answer 17

Damaged or incompletely replicated DNA

Question 18

What conditions in M would not allow the cell cycle to continue?

Answer 18

Chromosomes are improperly attached to mitotic spindle

Question 19

What is p53?

Answer 19

A key protein in the responses of cells to DNA damage

It is mutated in most human cancers when this process is deranged

Question 20

How do external signals regulate cell growth?

Answer 20

The availability of transmembrane growth factors receptors and extracellular growth factors can increase synthesis and enhance degradation of regulatory molecules

Question 21

What is a mitogen?

Answer 21

A substane that induces or stimulates mitosis

Question 22

What happens in the absence of mitogens?

Answer 22

Rb protein is dephosphorylated and active

This keeps a series of transcription factors in an inactive state

whose target genes are needed for cell proliferation

Question 23

What is Rb?

Answer 23

A key growth regulatory - mutations in Rb gene lead to abnormal Rb protein and abnormal cell cycle control