Cell cycle Flashcards
(15 cards)
What are the main phases of the cell cycle and the key events in each?
G1 phase: Cell growth, biosynthesis resumes, preparation for DNA replication
S phase: DNA replication, formation of sister chromatids
G2 phase: Quality control, preparation for mitosis
M phase: Mitosis (Prophase, Metaphase, Anaphase, Telophase)
What is the role of the G1 phase in the cell cycle?
Resumption of biosynthesis, growth, and production of proteins for DNA synthesis.
List the 6 hallmarks of cancer related to cell cycle dysregulation.
Self-sufficiency in growth signaling
Loss of proliferation inhibition
Evading apoptosis
Angiogenesis
Unlimited replicative potential
Invasion and metastasis
When are different types of cyclins highly expressed during the cell cycle?
Cyclin D: G1 phase
Cyclin E: G1/S transition
Cyclin A: S to G2 phase
Cyclin B: G2 to M phase
What is a cyclin-dependent kinase (CDK)?
An enzyme that regulates the cell cycle, only active when bound to a cyclin, and phosphorylates target proteins to drive cycle progression.
What is the function of Cdk1 and what cyclin does it pair with?
Cdk1 pairs with cyclin B to form MPF, which is essential for mitotic entry by phosphorylating proteins that prepare the cell for mitosis.
Give an example of CDK targets active in different cell cycle phases.
G1: p53, pRb
S: DNA polymerase, Mcm
G2: Cdc25 phosphatase
M: Histone H1, chromatin proteins
How is CDK activity regulated by phosphorylation?
Activation phosphorylation via CDC25
Inhibitory phosphorylation via WEE1/Myt1
What controls the subcellular localization of cyclin B1-Cdk1 and Cdc25C?
Phosphorylation status affects import/export; 14-3-3 binding prevents nuclear entry until prophase when phosphorylations allow nuclear translocation.
How is Cdc25C activated?
By phosphorylation (e.g., by PLK1 or CDK1), which enables it to remove inhibitory phosphates from CDK1.
What is the function of cell cycle checkpoints?
Prevent progression when DNA is damaged or replication is incomplete, allowing repair before continuation.
What are CKIs and how do they function?
CDK inhibitors (e.g., p16, p21) that block cyclin-CDK complexes by masking the substrate site.
How does proteolysis regulate cell cycle progression?
E.g., p27Kip1 is ubiquitinated and degraded, lifting inhibition on cyclin E-CDK2, allowing G1 to S transition.
What is endoreduplication and what causes it?
DNA replication without cell division; triggered by agents like Nutlin-3 and leads to genomic instability.
How are polyploid cells generated and why is this important in cancer?
Through unscheduled whole-genome duplications; leads to tetraploidy, a step toward aneuploidy and tumor progression.
