Cell Cycle Flashcards
What is Cell Turnover?
When damaged cells are replaced by normal cells through cell division
What is the order of the cell cycle?
G1, G0, Synthesis Phase, G2, Mitosis
What happens in G1?
- Cells synthesize mRNA and proteins needed for the next phase
- Cell grows and prepares for mitosis
- Cell decides whether or not to enter cell cycle
G1 is the longest phase of the cycle.
What happens in G0?
Cell recieves signal to temporarily or permenantly exit the cycle due to DNA damage or undesired proliferation conditions
reversable undesired conditions = quiscence
DNA damage = apoptosis
What happens in S phase?
Cells duplicate DNA
What happens in G2?
Cell reaches a checkpoint to check for any cell errors before continuing the cell cycle
What are some consequences of unchecked cell cycles?
Unequal chromosome segregation
- In somatic cells = Endoreplication (DNA duplicates, cells do not divide.)
What are Cyclins and CDKs?
A cyclin is an enzyme that, when binded with a Cyclind-Dependant Kinase (CDK), adds a phosphate group to target proteins that regulate processes like DNA replication, mitosis, and cell cycle checkpoints
Different combinations drives the cell to different points of the cell cycle.
Essentially, the CDK and cyclin complex is for driving the cell to its next cell cycle phase.
What is the difference between the extracellular signals for the cycle and CDK-Cyclin complexes.
Signals just tell the cells it’s good to go for cycle progression, the complexes are the internal machinery that execute cell cycle progression.
What is a restriction point?
A gateway in the late G1 phase that regulates gene expression needed for cell cycle progression.
What does progression rely on past the restriction point?
- Tumour suppressor, Retinoblastoma
- E2F family of transcription factors
In other words, the cell needs transcription factors and tumour suppressors to continue the cell cycle.
What kind of cyclins help with growth of cell during G1?
Expression of D-type cyclins. degradation of them will prevent cell cycle progression. Expression persists so long as the mitogenic (signal to start dividing) signal is still present.
e.g.) CyclinD/Cdk4/6: This complex binding causes phosphorylation to Retinoblastoma. This activates E2F which activates genes needed for DNA replication.
What are the CDKs-Cyclins involved in G1 and their functions? What happens when they are mutated
Rubisco is a protein in charge of stopping E2F from letting the cell go to the S phase
Cyclin D-CDK4/6 phosphorylates Rubisco and makes it lose its function, allowing it to go to S phase.
If it is mutated, it will constantly phosphorylate rubisco and cells will go to the S phase much quicker.
What are the CDKs-Cyclins involved in S-phase and their functions? What happens when they are mutated
CyclinA/E-CDK2 activates origin recognition complexes and duplication machinery to replicate DNA.
Mutation of so will duplicate DNA at an excessive rate.
What are the CDKs-Cyclins involved in G2 and their functions? What happens when they are mutated
CyclinA/B-CDK1 phosphorylate DNA-condensing proteins and prepares cell for mitosis.
Mutation of it will either not phosphorylate the proteins or cause premature entry of mitosis.
