Lecture 12 Review

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Questions and Answers

What happens to M-Cdk activity at the end of mitosis?

It is increased by cyclin degradation.

It is activated by spindle assembly.

It is inactivated by M-cyclin degradation. (correct)

It remains constant due to positive feedback.

What role does the APC/C protein complex play in the cell cycle?

It attaches ubiquitin to cyclin proteins. (correct)

It activates cyclins for cell cycle progression.

It inhibits the proteasome activity.

It synthesizes new M-cyclin proteins.

What is the purpose of poly-ubiquitylation of proteins in cells?

It signals proteins for destruction by the proteasome. (correct)

It marks proteins for promotion of activity.

It stabilizes proteins for longer activity.

It enhances protein folding and function.

What directly contributes to the loss of M-Cdk activity at the spindle-assembly checkpoint?

Degradation of M-cyclin protein levels. Signup and view all the answers

During the G2 phase of the cell cycle, what generally happens to the size of cells?

Cells decrease in size as growth normally continues. Signup and view all the answers

What is the significance of checkpoints in the cell cycle?

They prevent the initiation of cell division at inappropriate times. Signup and view all the answers

Which phase do cells enter if they stop dividing temporarily?

G0 phase Signup and view all the answers

What would be the consequence of a cell dividing before its DNA has fully replicated?

The daughter cells would lack complete genetic material. Signup and view all the answers

Which proteins are primarily responsible for regulating the cell cycle?

Cyclins and cyclin-dependent kinases Signup and view all the answers

How do cells ensure that all constituents are doubled before division?

Via checkpoint mechanisms Signup and view all the answers

What characterizes post-mitotic cells?

They never divide again. Signup and view all the answers

Which cell phase involves preparing for DNA synthesis?

G1 phase Signup and view all the answers

What triggers the progression of cells through the G1/S checkpoint?

Environmental signals Signup and view all the answers

What happens if a cell duplicates its DNA but fails to double its organelles before division?

Daughter cells will lack some organelles. Signup and view all the answers

Which regulatory mechanism is associated with the G2/M checkpoint?

Phosphorylation Signup and view all the answers

What happens when a checkpoint is 'activated' in the cell cycle?

Cell cycle stops or pauses Signup and view all the answers

Which protein plays a significant role as a regulator at the G1/S checkpoint?

p27 Signup and view all the answers

What state do cells enter when they temporarily leave the cell cycle?

Go state Signup and view all the answers

Which checkpoint is associated with the removal of Cdk inhibitor proteins?

G1/S checkpoint Signup and view all the answers

What is the consequence of p53 mutation in relation to the cell cycle?

Loss of cell cycle regulation Signup and view all the answers

Which checkpoint is responsible for ensuring that all chromosomes are properly aligned before proceeding?

Spindle assembly checkpoint Signup and view all the answers

What is the primary role of the Wee1 kinase in the cell cycle?

To phosphorylate and inhibit Cdk, regulating entry into M phase Signup and view all the answers

What consequence follows the loss of p53 function in a cell?

Increased accumulation of mutations Signup and view all the answers

Which statement accurately describes the role of Cdc25 phosphatase in the cell cycle?

It helps to activate M-Cdk, satisfying the G2/M checkpoint Signup and view all the answers

What is the primary function of cyclin-dependent kinases (Cdks) in the cell cycle?

To regulate the timing of cell cycle events Signup and view all the answers

What would likely happen to the cell cycle if Wee1 kinase were deleted?

Cells would go through M phase earlier than normal Signup and view all the answers

How do cyclin proteins affect the activity of Cdks?

They are required for the activity of Cdks Signup and view all the answers

What happens at checkpoint mechanisms in the cell cycle?

The cell is evaluated to ensure that previous phases are completed Signup and view all the answers

During which phase of the cell cycle does M-cyclin accumulate?

S and G2 phases Signup and view all the answers

What initiates the abrupt triggering of M-Cdk activity?

Accumulation of M-cyclin to a critical threshold Signup and view all the answers

Which cyclin is primarily associated with the M-phase of the cell cycle?

M-cyclin Signup and view all the answers

What is one role of the S-cyclin in the cell cycle?

To initiate DNA replication Signup and view all the answers

What process does active M-Cdk catalyze concerning Wee1?

Inactivates Wee1, removing its inhibitory effect on Cdk Signup and view all the answers

What phenomenon describes the relationship between Cdc25 and M-Cdk during the G2/M checkpoint?

A positive feedback loop enhancing M-Cdk activity Signup and view all the answers

Which of the following best describes a checkpoint in the context of the cell cycle?

A process that prevents the entry into the next phase until certain criteria are met Signup and view all the answers

Which checkpoint is responsible for ensuring that the DNA is not damaged before the cell cycle proceeds?

G2/M checkpoint Signup and view all the answers

What is required for the cyclin-dependent kinases (Cdks) to become active?

Binding with a type of cyclin Signup and view all the answers

Study Notes

Cell Division Cycle Overview

The cell cycle is crucial for ordered cell division, and defects can have serious consequences.
The cycle involves four stages, with specific events occurring in each.
Cyclins and cell cycle kinases control the progression through the cycle.
Checkpoints in the cycle ensure that one step is properly completed before the next begins.

Today's Topics

Overview of the cell cycle's four stages.
Cyclin-dependent kinases (Cdks) and their function.
The mechanisms of checkpoints.

The Cell Division Cycle Stages

Cell Growth and Chromosome Replication: The cell grows and duplicates its chromosomes.
Chromosome Segregation and Organelle Segregation: Chromosomes and organelles are segregated. This is the stage where the cell divides the replicated chromosomes and other material.
Cell Division: The cell physically divides into two daughter cells.

Cell Cycle Phases

Interphase: The period between cell divisions. Sub-divided into G1, S, and G2 phases.
G1 Phase: Growth and preparation for DNA replication (S phase).
S Phase: DNA replication.
G2 Phase: Growth and preparation for mitosis.
M Phase: Mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Cell Cycle Duration

Duration varies greatly between different cell types.
Examples include early fly and frog embryos (minutes), mammalian intestinal cells (hours), and mammalian fibroblasts (hours to days).

Challenges of Cell Division

Cells must precisely duplicate their contents and divide them equally between two daughter cells.
Errors in these processes can be catastrophic.

Cyclin-dependent Kinases (Cdks)

The activity of Cdks changes throughout the cell cycle.
Cdks require cyclins for their activity.
Variations in cyclin concentration throughout the cycle control Cdk activity and trigger specific events.

Checkpoints

Checkpoints ensure that one phase is completed before the next begins.
These are critical to cell cycle regulation
Essential for maintaining the integrity of the genome and preventing the creation of damaged cells.

G1/S Checkpoint

Cells decide whether to enter the cell cycle based on environmental signals.
Growth factors like epidermal growth factor (EGF) signal the cells to proceed.
Cells can temporarily leave the cycle at G0 and stop dividing.

G2/M Checkpoint

Checks if DNA is replicated correctly.
Checks for any DNA damage that needs repair before mitosis.

Spindle-Assembly Checkpoint

Ensures all chromosomes are properly attached to the mitotic spindle(s) before anaphase.
This assures equal division of chromosomes between daughter cells.

Mechanisms for Regulating Cdk Activity

Cdk inhibitor proteins
Phosphorylation
Protein degradation

M-Cdk Inactivation

M-cyclin degradation triggers M-Cdk inactivation.
APC/C is a protein complex responsible for this degradation.

Wee1 Kinase and Cdc25 Phosphatase

Wee1 kinase inhibits M-Cdk activity.
Cdc25 phosphatase activates M-Cdk activity.

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Description

Explore the intricacies of the cell division cycle, which is essential for ordered cell division. This quiz covers the four crucial stages of the cell cycle, the role of cyclins and cell cycle kinases, and the significance of checkpoints for accurate progression. Test your knowledge about cell growth, chromosome segregation, and the mechanisms involved.