Biochemistry L9 - Cell Cycle Control Flashcards Preview

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Flashcards in Biochemistry L9 - Cell Cycle Control Deck (18):

Give an example of a heterodimeric protein kinase involved in control of cell cycle

Cyclin-Cdk complex


Which is the regulatory and catalytic subunit of the cyclin-cdk complex

Regulatory = cyclin
Catalytic = cdk (cyclin dependent protein kinase)


How is kinase activity of cdk activated

When the right cyclin binds to cdk, kinase activity is activated


What does cyclin do

Tethers target protein so cdk can phosphorylate it


Why is cell cycle control crucial

Determines size and shape of organs/tissues,
Loss of control of the cell cycle can lead to cancer (uncontrolled cell division)


What drives cell cycle progression

Sequential activation of different cdk-cyclin complexes


Using G1 cdk-cyclin as an example, what are some of the actions of an activated cdk-cyclin complex

Activates transcription factors (turning on genes that encode DNA pol), activates genes for enzymes that produce deoxynucleosides, activates proteins involved in duplication of chromosomes, activates genes for subunits of next cdk cyclin complex


What allows the rb-E2F complex to dissociate so E2F can translocate to the nucleus and promote transcription

Phosphorylation of Rb by cdk-cyclin


What induces synthesis of G1 cyclins

Growth factors (mitogens)


In the absence of growth factors can the cell cycle go past the restriction point

No, the cell enters G0 phase


What protein does p53 activate



What does p21 do

Binds cdk-cyclin and inhibits kinase activity until DNA is repaired


What does p53 recognize

DNA mismatches/damage


What is ubiquitin

A small regulatory protein, binding of ubiquitin signals cyclin for degradation


What do checkpoints ensure

That chromosomes are present and that critical stages of cell cycle are completed before next stage begins, DNA is not damaged, spindles are properly formed and chromosomes are properly attached, and that the cellular environment is favorable


Concentration of which protein oscillates during a cell cycle?



Describe how levels of cyclin influence the cell cycle

Cyclin binds to CDK at the end of G1 phase. Cyclin levels then begin to lower as it is degraded, reducing the activity of the dimer. Towards the next phase, this G1 CDK-cyclin complex will activate the transcription factors for the cyclin for the following phase. Levels of this cyclin will build, and once they reach the right level, they'll bind to the appropriate Cdk, forming the dimer for the next phase.
AKA the Cyclin-Cdk complex of the previous phase triggers the production of the complex needed for the next phase.


What are the three mechanisms of controlling Cdk-Cyclin activity?

1. Degrading cyclin concentrations
2. Hyper-phosphorylating Cdk (2 P's are inhibitory)
3. P53 activates P21, which inhibits Cdk-cyclin complexes