Cell Cycle part 1 Flashcards
What regulates organ and body size?
Cell division, cell growth, and cell death.
What are the extracellular signals for cell growth, division and death?
Mitogens: stimulate cell division • Growth factors: Stimulate cell growth • Survival Factors: Promote cell survival by inhibiting apoptosis (cell death)
What are the cell cycle phases and their roles?
M phase - includes mitosis (nuclear division) and cytokinesis (cytoplasmic division)
G1 phase - cell growth and monitoring conditions
S phase- DNA replication
G2 phase- cell growth and monitoring conditions
What happens to the cell cycle when yeasts are shifted to a higher temperature?
The cell cycle is disrupted at a restrictive high temp, because the gene product required for progression for G1 to S is no longer functional. Differs from permissive low temp.
Describe the cell cycle control system.
Checkpoints occur at start causing entry to cell cycle and proceeding to S phase.
G2/M checkpoint causes entry into mitosis.
Metaphase to Anaphase checkpoint triggers anaphase and proceeds to cytokinesis.
What regulates the cell cycle control system?
Formation of Cyclin-Cdk Complexes along with
Transcriptional Regulation • • Phosphorylation/ Dephosphorylation • Protein Binding • Proteolysis/Degradation
Describe Cyclin-Cdk complexes -
regulate cell cycle events. Cdk activites rise and fall throughout cell cycle but levels stay the same. Cyclins regulate activities of Cdks and direct them to target proteins.
What are the major cyclin cdk complexes -
G1, G1/S, S, M Cdks
What do G1 cyclins do?
They regulate G1/S cyclins, produce S cyclins.
How is cdk regulated by cyclins?
Cyclin partially activates Cdk and Cdk activating kinase fully activates it.
How is the cyclin cdk complex regulated by phosphorylation and dephosphorylation?
Wee 1 kinase adds a phosphate, inactivating the complex, Cdc 25 phosphatase removes the complex, activating the complex.
How is the cyclin cdk complex regulated by protein binding?
p27 inactivates the complex.
What does the SCF complex do?
Causes ubiquitination and degradation of Cdk inhibitor protein in proteasome.
What does the anaphase promoting complex do?
Degrades m-cyclin, s-cyclin, and securin through ubiquitination.
What are mitogens?
Extracellular signal that stimulates cell proliferation. • Activates Ras/MAPK pathway • Promotes expression of immediate early gene expression.
What is the function of Myc -
important immediate early gene, increases expression of G1 cyclins, results in increased active G1-Cdk
What does G1-Cdk do?
phosphorylates and inactivates Retinoblastoma (Rb), so E2F proteins can become active.
• E2F protein promotes transcription of G1/S- and S-cyclins for progression into S phase.
Positive feedback occurs when G1/S cdk is bound by G1/S cyclin, keeping Rb off and keeping E2F on.
What does the E2F protein do?
It promotes transcription of G1/S and S cyclins for progression into S phase.
What is the role of the S-Cdk complex?
It phosphorylates ORC and helicase to start dna replication.
What do cohesins do?
Hold sister chromatids together along their length following DNA replication
Describe centrosome duplication:
triggered by G1/S-Cdk, occurs during S phase.
What is the role of the m-cdk complex?
Triggers assembly of condensin complexes for chromosome condensation • Induces separation of centrosomes and assembly of mitotic spindle • Ensures correct attachment of sister chromatids to the spindle • Breakdown of nuclear envelope (animal cells)
What do condensins do?
Execute chromosome condensation.
How is mitosis initiated?
Cdc25 activates M-cyclin via dephosphorylation.
It inhibits Wee1 through positive feedback and activates phosphatase through positive feedback.
