Exam 3 Flashcards
What occurs during the G1 phase?
G1 phase is a gap phrase to allow cells time to monitor cellular and environmental conditions before commitment to subsequent steps
Critical checkpoint known as the start transition (is the environment favorable?)
If satisfied cell cycle is entered and proceeds to S phase
Cells have single copies of genome in G1 phase
Longest phase
What occurs during S phase
DNA replication occurs so you end up with two copies of the chromosomes
G2 phase
Cell is monitoring cellular and environmental conditions before commitment to subsequent steps
Critical checkpoint G2/M transition (is all the DNA replicated? Is the environment favorable?) if this is satisfied proceeds to mitosis
M phase
Mitosis (nuclear division)
Breaking up genomic material
Cytokinesis (cytoplasmic division)
Breaking up the cytoplasmic material (forms two daughter cells)
Critical checkpoint: metaphase to anaphase transition (are all chromosomes attached to the spindle?) if so anaphase occurs and proceeds to cytokinesis
What are the steps of M phase
Prophase-breakdown of nuclear envelope (dissolution)
Prometaphase-an organization phase: need to arrange the paired sister chromatids
Metaphase-the paired sister chromatids are aligned along the metaphase plate
Metaphase to anaphase transition-assessing if once the cohesion is dissolved in the sister chromatids, the chromatids will go their separate ways (sister chromatid segregation)
Anaphase-all the cohesion broken down
Each of the individual sister chromatids is being pulled to opposite poles
Telophase
Starting to pinch in the cell membrane
Entering the cytokinesis phase. splitting up the cytoplasmic material
What are cyclins
Type of protein expressed at different times throughout the cell cycle to promote the functions associated with that portion of the cycle
When cyclin and cdk interact the complex becomes active
How does Cdk become active
In its inactive state, the active site is inaccessible
When cyclin binds to cdk it pulls the T loop out and becomes partially active
CAK then phosphorylates the T loop and causes a structural change that opens up the T loop so it is fully active
How is CDK regulated?
Can be inhibited by inhibitory phosphates and CKIs
Wee1 can add an inhibitory phosphate Cdc25 can reverse this
CKI binding causes rearrangement of the CDK active site rendering it inactive
M-Cdk feedback loop
Active M-CDK inhibits Wee1 and activates CDC25 To generate positive feedback loops
You are reducing rate of adding inhibitory phosphates and increasing rate of removing inhibitory phosphates
Causes powerful increases in cdk activity in a short amount of time
Cdk turnover by APC/C
Metaphase to anaphase you need to turn off cyclin
You turn on APC/C (anaphase promoting complex)
Once cdc20 is added to APC it becomes active and binds to M-cyclin and can ubiquinate it. (Causes destruction of cyclin)
Protein turnover by SCF
SCF can recognize the CKI after phosphorylation
Can then quickly degrade the CKI for an active CDK complex
What happens if DNA damage is found?
Certain CDK will be inhibited so cycle doesn’t proceed to next step
