Cell Cycle

Question 1

What is the function of Cdk1 and cyclins and what is an MPF?
How does the complex induce mitotic entry?

Answer 1

MPF = complex of a cyclin and a CDK.
Cdk1 is catalytic subunit of MPF = a kinase.
Cyclins determine substrate specificity and sub cellular localisation of kinase.
Phosphorylation of many structural proteins required for mitosis –> nuclear envelope breakdown, chromosome condensation, spindle assembly.

Question 2

How do we know there are additional controls regulating the behaviour of the cyclin CDK complex.

Answer 2

activation of Cdk1 is more abrupt than simply accumulation of cyclin.
(additional controls = kinases and phosphatases).

Question 3

What is CAK and how does it lead to full activation of Cdk/cyclin complex?

Answer 3

A cyclin-dependent kinase (complex of CDK7/ Cyclin H)

Phosphorylates T161 in T loop of Cdk.

Question 4

What are the inhibitory phosphates?

Answer 4

Cyclin binding to Cdk exposes Y15 and T14 in active site

Wee1 or Myt1 can phosphorylate these –> prevents ATP binding in Cdk active site.

Question 5

What and where is the destruction box?

Answer 5

At the N terminus of cyclin lies a sequence required for its proteolysis.
Proximal to this box are numerous lysine residues required for ubiquitination.

Question 6

What happens after cdc20 dissociates from APC/C?

Answer 6

Replaced by Hct1 which maintains APC/C activity throughout G1 so any mitotic cyclins produced can be degraded. (G1 and S-Cdk complexes not targeted).

Question 7

How is the SAC targeted in cancer therapies?

Answer 7

Taxanes (taxol) - STABILISE MTs - prevent capture of chromosomes and –> SAC engagement.
Vinca alkyloids (nocodazole) - PREVENT mt POLYMERISATION –> SAC engagement.
Persistent M phase induced by SAC activation –> mitotic catastrophe and cell death.

Question 8

What type of spindle attachment is particularly tumourigenic?

Answer 8

Merotelic - mal-orientated and partial tension, difficult for SAC to detect and leads to large scale aneuploidy.