Lecture 22: Cell cycle regulation

Question 1

WhatisaCDK?What does it do? Whatotherproteinisrequiredtobindtoitforactivity?

Answer 1

Cyclin dependent kinases. Protein. Requires the binding of cyclin to work. REGULATES proteins that carry out the cell cycle functions; in charge of them

Question 2

HowmanyCDKsandcyclinsdoanimalshave?

Answer 2

8 CDKs, 10 Cyclins

Question 3

TrueorFalse:TheabundanceofCDKproteinscycleswiththecellcycle,whilethe
abundanceofcyclinproteinsisstable

Answer 3

FALSE. CDK is stable, Cyclin abundance changes

Question 4

Trueorfalse:TheactivityofCDKscycleswiththecellcycle

Answer 4

True

Question 5

WhatistheT‐loop,andwhatdoesitdoduringregulationofCDKactivity?

Answer 5

Is a structure on CDK that blocks the active site where cyclin binds

Question 6

WhatistheimportanceoftheDestructionbox?Whatrecognisesthissequenceandwhathappens when it binds it?

Answer 6

• Is a recognition sequence that binds to the protein that will later be degraded.
• It attaches UBIQUITIN as the ‘marker’

Question 7

Doesthebindingofp21activateorinhibittheactivityofCDK?

Answer 7

Inhibit

Question 8

What is the G0 phase?

Answer 8

Cells that are not going through the cell cycle sit here. They ARE able to rejoin the cycle

Question 9

How is the cell cycle regulated? Name the 4 different ways.

Answer 9

1. Phosphorylation: can inactivate or activate the cycle
2. Degradation: controlled destruction of protein
3. Synthesis
4. Protein-protein interactions; i.e inhibitory proteins

Question 10

Why does the abundance of cyclin vary during the cycle?

Answer 10

Because cyclin undergoes protein synthesis and degradation

Question 11

What are the classes of cyclins? describe them.

Answer 11

They bind to CDK at certain points (checkpoints) in the cell cycle to regulate cell cycle.
G1/S: starts the cell cycle
S: helps throughout, stays the longest
G2/M: rises before mitosis then drops when it enters mitosis

Question 12

How is the t-loop in CDK moved?

Answer 12

By the binding of cyclin.

Question 13

How does CDK become fully activated?

Answer 13

1. Cyclin must bound first
2. Thr160 must be phosphorylated
3. Glutamine moves into the active site

Question 14

How does CDK become inactivated?

Answer 14

Phosphorylation of Tyr15. blocks the ATP binding site; Holds CDK in an inactive state till needed.

Question 15

What are proteasomes?

Answer 15

It has to do with the DBRP: destruction box. degrades proteins back to amino acids

Question 16

GivethreeexamplesoftargetproteinsofCDKs.Forallthree,whichphaseofthecellcycle
isitphosphorylated,andwhathappenswhenitisphosphorylated?

Answer 16

1. Nuclear lamins: mitosis: nuclear membrane breaks down
2. Condensins: mitosis: condenses DNA
3. Rb: G1/S:

Question 17

WhatistheroleoftheproteinRb1?

Answer 17

is a tumour repressor gene; without it, cancer may develop

Question 18

whatisanoncogene?

Answer 18

Opposite of Rb. so if they are suppressed, then cancer may arise

Question 19

WhatisKnudson’stwo‐hithypothesis?

Answer 19

Person starting with mutation in one half of the chromosome more likely to develop the disease

Question 20

Whatisthemechanismbywhichadoublestrandedbreakcausesacellcyclearrest?How
isthisarrestrelivedoncethebreakisrepaired?

Answer 20

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