Control of the Cell Cycle

These flashcards cover key concepts related to the control of the cell cycle, including mechanisms, phases, and regulatory proteins.

What are the phases of the cell cycle?

G0, G1, S, G2, and M phases.

Interphase: G1, S, G2: 95% of dividing cells time spent in interphase

G1: Gap 1, interval between mitosis and DNA replication. Time for cell growth

S: Replication of DNA

G2: Gap 2, second growth phase to prepare for cell division.

M: Mitosis and Cytokinesis

• prophase - chrs condense, mitotic spindle assembled, DNA disentangles and condenses into sister chromatids, still linked by sister chromatid cohesion

• prometaphase - nuclear envelope breaks down. sister chromatids attached at opposite ends of mitotic spindle.

• metaphase - chrs align at equator of spindle

• anaphase - sister chromatid cohesion breaks down

• telophase - daughter chrs at opp poles of spindle, nuclear envs assemble, spindle disassembles

• cytokinesis - cell cleavage

What is the role of cyclins in the cell cycle?

Cyclins regulate the activity of cyclin-dependent kinases (CDKs). They activate CDKs by binding to them.

Cyclical changes in cyclin concentration are specific to the phase, and cyclins are classes by the phase in which they function.

What is the function of cyclin-dependent kinases (CDKs)?

CDKs are enzymes that drive the cell cycle by phosphorylating other proteins.

Define mitosis.

Mitosis is the process of replicating and dividing the nucleus.

• prophase - chrs condense, mitotic spindle assembled, DNA disentangles and condenses into sister chromatids, still linked by sister chromatid cohesion

• prometaphase - nuclear envelope breaks down. sister chromatids attached at opposite ends of mitotic spindle.

• metaphase - chrs align at equator of spindle

• anaphase - sister chromatid cohesion breaks down

• telophase - daughter chrs at opp poles of spindle, nuclear envs assemble, spindle disassembles

What triggers the metaphase-to-anaphase transition?

It is triggered by the Anaphase-Promoting Complex (APC/C) through the proteolysis of S- and M-cyclins.

APC/C is a unbiquiting ligase enzyme, by tagging cyclins with ubiquitin, it marks them for destruction by proteasomes

What occurs during the G1 phase?

Cell growth and preparation for DNA synthesis; it is the interval between mitosis and DNA replication.

What is the significance of the S phase?

DNA replication occurs during this phase, ensuring all chromosomes are copied once and only once.

Describe the role of condensin in mitosis.

Condensin compacts chromosomes and helps separate sister chromatids.

How does S-CDK contribute to DNA replication?

S-CDK initiates DNA replication at origins of replication once per cell cycle.

What is the role of cohesin during the cell cycle?

Cohesin holds sister chromatids together until anaphase.

What is the function of CKI proteins?

CKI proteins inhibit the activity of cyclin-CDK complexes, acting as regulators.

Why must DNA replication be complete before chromosome segregation?

To ensure each daughter cell receives an identical set of chromosomes.

What is the APC/C and what does it do?

APC/C is a ubiquitin ligase that targets cyclins for destruction, facilitating cell cycle transitions.

What is the main role of CDK-activating kinase (CAK)?

CAK phosphorylates CDKs and fully activates them.

What happens during cytokinesis?

The cytoplasm divides, forming two separate daughter cells.

What role does Cdc25 play in the cell cycle?

Cdc25 is a phosphatase that removes inhibitory phosphates from CDKs, activating them.

What is the effect of p53 in the context of DNA damage?

p53 activates CKIs and halts the cell cycle for repair.

Define anaphase.

Anaphase is the stage where sister chromatids are pulled apart to opposite poles of the cell.

How do mitogens influence the cell cycle?

Mitogens stimulate G1-CDK and G1/S-CDK activity, promoting cell cycle progression.

What effect does phosphorylation have on CDK activity?

Phosphorylation can either activate or inhibit CDK activity.

What is the significance of checkpoint proteins in the cell cycle?

Checkpoints ensure that critical processes are completed correctly before the cell proceeds to the next phase.

What triggers entry into mitosis from G2?

An increase in M-cyclins and the subsequent activation of M-CDK.

What is the function of the mitotic spindle?

The mitotic spindle organizes and separates chromatids during mitosis.

Describe the difference between anaphase A and anaphase B.

Anaphase A involves shortening of kinetochore microtubules, while anaphase B involves the movement of spindle poles apart.

What is the relationship between the cell cycle and cancer?

Mutations in cell cycle regulatory genes can lead to uncontrolled cell division, contributing to cancer.

How does the CDK inhibitor p27 function?

p27 inhibits G1/S and S-CDK activities, helping cells withdraw from the cell cycle.

Causes and induced conformational change of the CDK active site, that inactivates it.