Cell cycle 2 Flashcards
S phase
dna replication and chromosome duplication
M phase
mitosis and cytokinesis
Cell cycle control system
Cyclically activated cyclin dependant protein kinases
Whats a cyclin-cdk complex formed off
cyclin activates cdk.
G1 cyclins
Cyclins bind and activate cdks, stimulate entry into a new cell, concentration depends on rate of cell growth
S cyclins
Cyclins that activate cdk for dna synthesis, remains high in S phase
M cyclins
Cyclins that activate CDKS for mitosis, peaks in metaphase
What does cyclin do other than activate CDKs?
directs the complex to specific target proteins, phosphorylating different substrate proteins
Explain how CDK can become active through cyclin activation
In inactive state, T loop blocks active site. Once cyclin binds to CDK T loop structure changes and CDK becomes active as cyclin binds to it
Explain mechanism of wee1 and cdc25 regulatory pathway
Active CDK complex can be inhibited by further phosphorylation in active site. Phosphorylation of try is by wee1
Cdc25 can dephosphorylate this site and lead to activation
Explain how CDK inhibitor proteins affect binding of cyclin
CKL is an inhibitor protein which binds to the active site of CDK, making binding of cyclin not possible.
Explain role of RB and e2f
RB is a tumour supressor protein that prevents uncontrolled cell proliferation
E2F is a transcription factor that controls expression of genes essential for DNA synthesis
Explain process of growth factors leading to production of CDK and cyclin complex and effect the complex has on RB and E2F
in early G1 phase a growth factor leads to RAS pathway which stimulates formation of CDK and cyclin, this complex phosphorylates RB, causing a conformational change, leading to e2f being freed and gene expression continuing.
Whats the role of the Ubiquitin pathway
essentially leads to degradation of specific proteins in a chain of reactions
Whats the main role of ubiquitin
It targets a protein that needs to be degraded via a proteosome
What is a proteosome
a large protein complex which degrades polyubiquated proteins
how do proteosomes work
they recognize proteins marked by a polyubiquitin chain, ubiquitin is recycled at an early stage.
Explain translocation mechanism
protein is translocated into proteosome core, where ATPases unfold substrate protein, a hyrolyse cleaves ubiquitin from protein, where it is recycled.
Explain role of E1
Ub activating enzyme
Explain role of E2
is the conjugating enzyme, where UB is transferred from E1 to E3
Explain role of E3
attatches UB to target protein, making protein ready to be detected by proteosome
What is the APC
Anaphase promoting complex: is a large E3 ubiquitin ligase complex, which ligases ubiquitin to a target protein
Explain role of the APC
Promotes transition from metaphase to anaphase , targeting proteins for degradation.
What is securin
is tagged for degredation, allows seperase to cleave cohesins, enabling sister chromatid seperation
What happens to cyclins
they are degraded, and inactivated
How is the APC activated
via co activators, cdc20 activates APC during metaphase to anaphase transition
how does cdh1 play a role
maintains APC during M phase and G1
