Cell Cycle (CH 19) Flashcards
stages of cell cycle
Gap1, S-phase, Gap 2, Mitosis
Gap 1
cell grows in size, synthesize RNA & proteins needed for DNA synthesis
S-phase
chromosome replication, each copy connects as sister chromatids
Gap 2
cell prepares for mitoses
Mitosis
beginning: nuclear membrane breaks down, retracts to ER, golgi breaks into vesicles, microtubles break down and reassemble into mitotic apparatus, and spindle pole forms and associate with kinetochore
end: sister chromatids move to ends of cell, mitotic spindle disassembles
cyclin
regulatory subunit;
G1 or
B-type (cyclin B&A)- have destruction box w/ APC/C Cdh 1
CDK
cyclin dependent kinase that phosphorylates proteins
Mid G1 cyclin-CDK
activate transcription factors that induce gene expression needed for DNA synthesis and S-phase cyclin and CDKs
(Cyclin D-CDK4 and Cyclin D-CDK6)
Late-G1 cyclin-CDK
phosphorylate inhibitors to activate SCF (ubiquitin protein ligase - leads to inhibition of inhibitors to release S-phase cyclin-CDKs)
(Cyclin E-CDK2)
S-phase cyclin-CDK
phosphorylate proteins, initiate DNA replication, and inhibit reassembly of complexes to ensure single replication
(Cyclin A-CDK2)
Mitotic cyclin-CDK
activated by dephosphorylation; phosphorylates substrates
(Cyclin A-CDK1
Cyclin B - CDK1)
role of Rb and E2F proteins in cell cycle progression
Rb (retinoblastoma) - blocks cell cycle progression by inhibiting activity of E2F transcription factors. Hypophosphorylated Rb binds E2F, blocking it from binding to promoter. In
Mid G1 CyclinD-CDK4/6 phosphorylate Rb. In Late G1: CyclinE-CDK2 hyperphosphorylates Rb, releasing E2F and allowing gene transcription.
E2F regulates expression of genes needed for DNA replication, cyclin-CDKs, etc.
early response genes
induced by transcription factors already present in the cell (CREB, SRF, etc)
late response genes
require new protein synthesis; dependent on transcription and translation of early response genes (include transcription factors & Cyclin-CDKs needed for cell cycle progression)
APC-mediated degradation of mitotic cyclins
Late anaphase:
APC/C is active (bound to Cdh1). APC/C polyubiquitinates mitotic cyclin (A/B) for degragation by proteasome. Kinase activity declines to trigger telophase. G1-cyclin CDK phosphorylates Cdh1, does not associate with APC/C making it inactive.
Prophase:
Mitotic cyclin is synthesized. Cdc14 removes phosphate from Cdh1, allows to activate APC/C.
