Cell cycle control

Question 1

why is cell cycle under strict and complex control?

Answer 1

since its disturbance leads either to cell death or to cancer development

Question 2

how can cell cycle be distributed?

Answer 2

by chemical or physical agents directly or indirectly

Question 3

mutation of genes that encode cell cycle regulatory proteins is usually at what origin?

Answer 3

at the origin of abnormal cell cycle

Question 4

what does alteration of signalling pathways that involve oncogenes also lead to?

Answer 4

may also lead to uncontrolled cell cycle

Question 5

what is the most important check point in the cell cycle?

Answer 5

at the end of G1, the G1-S transition

Question 6

what happens if a cell passes this gap? what is its benefit?

Answer 6

it will necessarily continue S, G2 and M simply in order to avoid wasting energy

Question 7

DNA replication must necessarily be followed by what? what happens to the replicated DNA otherwise?

Answer 7

DNA replication must necessarily be followed by cell division, otherwise the replicated DNA would be useless

Question 8

What is the other check point?

Answer 8

the G2-M transition

Question 9

what did cell fusion experiment between cells in different stages of the cycle reveal?

Answer 9

revealed the presence of cytoplasmic factors that control nuclear activity and cell cycle

Question 10

what do the members of the MPF-like family (maturation promoting factor-like) have?

Answer 10

phosphorylation activity

Question 11

kinase activity of MPFs is dependent on which family?

Answer 11

the cyclin family

Question 12

what is concentration of cyclins considered as and what happens to concentration as the cell cycle progresses?

Answer 12

the regulatory subunits of MPFs, rises and falls in a predictable pattern as the cell cycle progresses

Question 13

why are they named cyclins?

Answer 13

because their amounts vary in a cyclic manner

Question 14

how many families are known? name them and say when is their peak.

Answer 14

2 families are known, the G1 cyclins whose peak is during G1 and mitotic cyclins whose peak is just prior to mitosis

Question 15

what do cyclins control?

Answer 15

control the activity of MPFs

Question 16

what are MPFs therefore referred to as and why?

Answer 16

cyclin-dependent kinases (Cdk or cdc) since they are active only when the 2 subunits are assembled

Question 17

how does MPF promotes initiation of M phase? what does this MPF consist of?

Answer 17

MPF that promotes initiation of M phase by activating G2-M transition, consists of a first subunit named cdc2-kinase (serine/threonine kinase) and a second regulatory one which is a “mitotic cyclin” whose concentration is maximum in the G2 phase

Question 18

what does the activated MPF trigger and how? what do these specific proteins initiate?

Answer 18

triggers M phase by phosphorylating specific proteins (whose conformations are changed upon phosphorylation) which initiate mitosis

Question 19

give example on proteins that are activated by such phosphorylation.

Answer 19

proteins which initiate condensation of chromatin into chromosome and those that induce cytoskeleton change are activated by such phosphorylation

Question 20

what does the same cdc2-kinase enhance and when?

Answer 20

the same cdc2-kinase enhances the G1-S transition when it dimerizes with one of the G1 cyclins whose maximum concentration is reached by the end of G1

Question 21

what will the cdc2-kinase assembled with G1 cyclins phosphorylate do?

Answer 21

another set of proteins that induce DNA replication and histone synthesis