Phys Conc 6 - Cell Cycle Flashcards
what is the cell cycle?
the orderly sequence of events by which a cell duplicates its contents and divides in 2
what are the 2 main phases of the cell cycle
mitotic phase and interphase
what are the subphases of interphase
- G1 phase
- S phase
- G2 phase
- G0 phase
what is the G1 phase?
first gap phase
- preparatory growth phase prior to cell entering DNA synthesis phase
- cell is metabolically active
- many organelles are duplicated but no DNA replication
- 6-24 hours
what is the S phase?
DNA and chromosomal protein synthesis occurs
7-8 hours
cell is NOT committed to cell division
- DNA replication occurs here
what is the G2 phase?
Second growth phase
- interval between DNA synthesis (S phase) and mitosis (M phase)
- enzyme, protein, and ATP synthesis occurs here
what is the M phase?
mitotic phase
- cell undergoes mitosis and then cytokinesis
1-2 hours
what is the G0 phase
state of withdrawal from cell cycle
- cell is neither dividing nor preparing to divide
the cell is “doing its job”
what are the features of the cell cycle control system?
- generally binary (on/off) to launch an event in complete and irreversible fashion
- robust and reliable - contains back up mechanisms
- adaptable and modified to suit specific cell types - adaptable and modified to suit specific cell types
what are checkpoints (transitions)
points in the cell division cycle where progress through the cycle can be halted until conditions are suitable for the cell to proceed to the next stage
what are the 3 main regulatory transitions?
- start transition (G1/S)
- G2/M transition
- metaphase to anaphase transition ( M to A)
what is the rate limiting and committing step of the cell cycle?
G1/S checkpoint
what are cyclin dependent kinases? (cdks)
there are enzymes that are responsible for cyclical changes in phosphorylation of intracellular proteins that initiate/regulate the major events of the cell cycle
cdks are controlled by a group of proteins called ?
cyclins
what is needed to progress through a checkpoint?
cyclin-cdk complexes
(except M-A checkpoint)
what are the 4 classes of cyclins we need to know?
- cyclin D
- cyclin E
- Cyclin A
- Cyclin B
what is the G1 cyclin and what complex does it form with
cyclin D forms complex with Cdk 4 or Cdk6
- needed for initiation of transcription of G1/S cyclins
what is the G1/S cyclin and what complex does it form with?
Cyclin E forms complex with Cdk2 and helps trigger progression through start transition
what is the S-cyclin and what complex does it form with?
Cyclin A forms complex with cdk1 and cdk2
- helps stimulate chromosome duplication during S phase
what is the M cyclin and what complex does it form with?
Cyclin B forms complex with cdk1 and it stimulate entry into mitosis at the G2/M transition
other than simply activating the cdk what else does the cyclin do?
directs it to a specific target protein
explain the metaphase-to-anaphase checkpoint
occurs via regulated protelysis
need APC/C (anaphase promoting complex) and it polyubiquitinates specific target proteins for destruction in proteasomes
what happens at the G1/S checkpoint
active G1-cdk and G1/S-cdk complexes will target a protein called RB and phosphorylate it
Inactive RB then releases a transcription factor E2F allowing transcription to proceed
what is RB
a transcription co-repressor specifically E2F
