cell division

Question 1

which cdk and cyclin are responsible for controlling G1 up until the R (restriction point) checkpoint?

Answer 1

cdk 4/6

cyclin D

Question 2

which cdk and cyclin complex is responsible for the control of G1 (after R point) to beginning of S phase?

Answer 2

CDK2 and cyclin E

Question 3

which cdk and cyclin complex is responsible for the beginning of S phase into the middle of S phase?

Answer 3

CDK 2 and cyclin A

Question 4

which CDK and cyclin are responsible for the middle of S phase into the end of G2 phase?

Answer 4

CDK 1 and cyclin A

Question 5

which CDK and cyclin are responsible for M phase?

Answer 5

CDK 1 and cyclin B

Question 6

what is ubiquitination?

Answer 6

ubiquitin is attached to an enzyme via a covalent band, then onto an E2 enzyme then the ubiquitin is transferred by a ligase enzyme onto a substrate via a lysine group - the third ligase enzyme is specific for different proteins

Question 7

how are ubiquitinated proteins broken down?

Answer 7

by proteasomes - the lid of the proteasome binds to the ubiquitin and the protein passes through the channel and is degraded

Question 8

why do events in the cell cycle only fire once?

Answer 8

1. cdc6 is a component of the pre-replicative complex which binds to the origin of replication of DNA. This is degraded once cdc6 has been phosphorylated and subsequently caused the breaking up of the replicative complex. cdc 6 is broken down irreversibly.
2. cyclin is broken down by ubiquitination and proteosomes and so must be regenerated before the CDKs can be activated again

Question 9

which inhibiting factor is responsible for the inhibition of CDK4 and cyclin D which prevents the cell cycle from going past the R point?

Answer 9

p16

Question 10

how does cdk4 and cyclin D allow entry into S phase?

Answer 10

cdk4 plus cyclin D phosphorylates the Rb which is preventing the transcription of S phase genes

Question 11

what is p53?

Answer 11

a transcription factor which promotes the transcription of cdk inhibition factors

Question 12

what are the 4 main phases of mitosis?

Answer 12

prophase - condensation of DNA by condensing proteins
metaphase - lining up of chromosomes on the metaphase plate and attachment to the spindle fibres
anaphase - initiation of separation of sister chromatids to opposite poles
telophase - completion of separation of chromatids

Question 13

where do spindle fibres attach to the chromosomes?

Answer 13

at kinetochores on the centromeres

Question 14

what is the name of the protein rings which bind DNA together in prophase?

Answer 14

cohesin

Question 15

what is the name of the enzyme which breaks down cohesion at anaphase?

Answer 15

separase

Question 16

what is the name of the protein which inactivates separase?

Answer 16

securin - broken down by ubiquitination