Cell Cycle Regulation: Checkpoints and CDKs

Questions and Answers

What is the result of phosphorylating the RB protein?

It becomes active and inhibits DNA replication

It remains unchanged and continues to inhibit DNA replication

It becomes inactive and can't inhibit DNA replication (correct)

It becomes active and promotes DNA replication

In which phase of the cell cycle is cyclin A produced?

G2 phase

S phase (correct)

G1 phase

M phase

What is the role of the cyclin B CDK-1 complex?

To activate mitosis (correct)

To inhibit mitosis

To inhibit DNA replication

To activate DNA synthesis

What is the purpose of cyclin proteins in the cell cycle?

To promote DNA synthesis Signup and view all the answers

What is the complex that phosphorylates the RB protein?

CDK-4 cyclin D complex Signup and view all the answers

What is the result of having cyclin proteins present during the cell cycle?

DNA synthesis is promoted Signup and view all the answers

What is the main purpose of the regulation of the cell cycle?

To prevent uncontrolled cell growth Signup and view all the answers

Where are the two key places of regulation in the cell cycle?

Between G1 and S, and between G2 and M phase Signup and view all the answers

What do cyclin-dependent kinases (CDKs) do to other enzymes or proteins?

Add a phosphate group Signup and view all the answers

What is the default form of cyclin-dependent kinases (CDKs) in a cell?

Inactive Signup and view all the answers

What is required for a cyclin-dependent kinase (CDK) to be active?

The binding of a specific cyclin Signup and view all the answers

What type of cyclins are produced in the G1 phase?

Cyclins D and E Signup and view all the answers

What is the function of the complex formed by CDK-2 and cyclin E?

To regulate the G1 to S phase transition Signup and view all the answers

Why are specific cyclins produced at specific times in the cell cycle?

To regulate the cell cycle and prevent uncontrolled growth Signup and view all the answers

Study Notes

Cell Cycle Regulation

The cell cycle is a regulated process with two key checkpoints: one between G1 and S phase, and another between G2 and mitosis.
Cyclin-dependent kinases (CDKs) are key regulators of the cell cycle, and they work together with cyclin proteins.
CDKs are always present in cells, but they are inactive by default and need to be activated by cyclin proteins.
Specific cyclins are produced at specific times in the cell cycle, and CDKs are only active when bound to a specific cyclin.

G1 Phase

Cyclins D and E are produced in the G1 phase.
CDK-2 binds to cyclin E, and CDK-4 binds to cyclin D, forming active kinase complexes.
The CDK-4 cyclin D complex phosphorylates the RB protein, inactivating it and allowing DNA replication to proceed.

S Phase

Cyclin A is produced in the S phase.
Cyclin A complexes with CDK-2 to activate DNA replication.

G2 Phase

Cyclin B is produced in the G2 phase.
The cyclin B CDK-1 complex is formed, which activates mitosis or cell division.

Checkpoints

The presence of specific cyclin proteins is necessary to pass through the checkpoints and allow the cell cycle to proceed.
Cyclin proteins inhibit proteins that block DNA synthesis or replication, and promote the production of proteins needed for mitosis.