QuestionSBA
QuestionChoice
This occurs during the initiation of the cell cycle and is stimulated by mitogen pathways. It results in E2F1 promoting the transcription of Cyclin E. Excess CDK4-Cyclin D activity due to gain of function or over-expression is a common mechanism utilised by breast cancer cells and glioblastomas.
10001119
d
CDK4-Cyclin D phosphorylates retinoblastoma protein, dissociating it from E2F1
QuestionChoice
This process occurs normally during the cell cycle, acting as a molecular switch. APC-CDH1 ubiquitinates Cyclin A to cause its degradation. CDK2-Cyclin A binds and phosphorylates CDH1, inactivating APC-CDH1. In G1, Cyclin A synthesis is low so APC-CDH1 predominates however, once the synthesis of Cyclin A is sufficient, the balance is shifted and CDK2-Cyclin A inhibition of APC-CDH1 predominates. The resultant rise in CDK2-Cyclin A promotes the shift from G1 to the S-phase.
10001118
c
CDK2-Cyclin A is activated, activating a negative feedback loop on APC-CDH1
QuestionChoice
Once these kinases are activated, one of their actions is to phosphorylate Chk1/2 kinases which phosphorylate Wee1 kinase and Cdc25 phosphatase, activating and inhibiting them respectively. This results in increased phosphorylation of CDK1, inhibiting CDK1-Cyclin B complexes and inhibiting cell cycle progression at the G2/M checkpoint. This is known as the DNA damage checkpoint.
10001116
a
ATM/ATR kinases detect the free ends of damaged DNA
QuestionChoice
APC-CDC20 does ubiquitinate Cyclin B to promote its proteasomal degradation, but this is a normal process in mitosis, occurring at the start of anaphase alongside the degradation of securin and allowing the chromatids to separate.

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10001120
e
APC-CDC20 promotes the degradation of Cyclin B, inhibiting G2/M progression
QuestionChoice
These SMADs activate p107 binding to E2F4 which represses transcription of Cyclin E. SMADs also activate p15-INK4b which in turn represses CDK4-Cyclin D to further decrease Cyclin E transcription. This describes the inhibition of replication by external signals which prevents the G1/S transition, rather than the DNA damage checkpoint.
10001117
b
Anti-mitogens such as TGF-B bind receptors, activating SMADs
Concept
Chapter
2693
3885
Processes in mitosis
Topic
156
Medical Genetics
12770
Upon DNA damage, which of these processes occur as part of a mechanism to prevent cell cycling until the damage is repaired?
a