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Cyclins vs. Cyclin Dependent Kinases: What's the Difference?

Edited by Aimie Carlson || By Harlon Moss || Published on March 15, 2024
Cyclins regulate the cell cycle by activating cyclin-dependent kinases (CDKs), which are enzymes essential for cell division.

Key Differences

Cyclins are regulatory proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinases (CDKs). Cyclins undergo periodic changes in concentration, which regulate the activity of CDKs, thereby ensuring the proper timing of cell cycle events. Cyclin-dependent kinases (CDKs) are enzymes that, when activated by binding to cyclins, phosphorylate specific target proteins to initiate or regulate key events in the cell cycle.
The interaction between cyclins and cyclin-dependent kinases is crucial for the cell cycle's checkpoints, which are mechanisms that ensure the fidelity of cell division. Cyclins bind to CDKs, activating them at specific points in the cell cycle, leading to the phosphorylation and regulation of downstream proteins that drive the cell cycle forward.
Cyclins are characterized by their periodic synthesis and degradation, which corresponds to specific phases of the cell cycle. This cyclical nature ensures that cyclin-dependent kinases are activated only at the appropriate times, preventing premature or unregulated progression through the cell cycle.
Cyclin-dependent kinases, by contrast, rely on the presence and binding of cyclins for their activity. The specificity of this interaction allows for precise control of the cell cycle, as different cyclins are expressed at different stages, thereby activating different CDKs and targeting different substrates involved in cell cycle progression.

Comparison Chart


Activate CDKs
Phosphorylate specific target proteins


Concentration varies with cell cycle
Activity regulated by cyclin binding

Role in Cell Cycle

Control timing of cell cycle events
Execute cell cycle events by phosphorylating substrates


Periodically synthesized and degraded
Constant concentration, activity regulated by cyclins

Interaction with Other Proteins

Bind to and activate CDKs
Bind to cyclins for activation

Cyclins and Cyclin Dependent Kinases Definitions


Cyclins are proteins that regulate the cell cycle.
The level of cyclins increases during the S phase to prepare the cell for DNA replication.

Cyclin Dependent Kinases

CDKs require cyclins for activation.
CDK2 remains inactive until it binds with cyclin E or A.


Cyclins are crucial for the activation of CDKs.
Without cyclins, CDKs remain inactive and the cell cycle cannot proceed.

Cyclin Dependent Kinases

Cyclin-dependent kinases (CDKs) are enzymes that drive the cell cycle.
CDK1 is essential for the transition from G2 to M phase.


Different cyclins are specific to different phases of the cell cycle.
Cyclin D is important for the transition from G1 to S phase.

Cyclin Dependent Kinases

CDKs phosphorylate specific substrates to advance the cell cycle.
CDK4 phosphorylates Rb protein, allowing the cell to pass the G1 checkpoint.


Cyclins undergo regulated synthesis and degradation.
Cyclins are degraded through ubiquitin-mediated proteolysis after their function is fulfilled.

Cyclin Dependent Kinases

The activity of CDKs is tightly regulated.
CDK inhibitors can halt the cell cycle by preventing CDK activation.


Cyclins function as regulatory subunits.
Cyclins bind to CDKs, changing their conformation and activating their kinase activity.

Cyclin Dependent Kinases

CDKs are present throughout the cell cycle but active only when bound to cyclins.
CDK6 is present in G1 phase but needs cyclin D to become active.


Any of a class of proteins that fluctuate in concentration at specific points during the cell cycle and that regulate the cycle by binding to a kinase.


Plural of cyclin


What are cyclins?

Cyclins are regulatory proteins that control the cell cycle phases by activating cyclin-dependent kinases.

Why are cyclins important?

Cyclins ensure that cell cycle events occur at the correct time and order.

What do cyclins do?

Cyclins bind to and activate CDKs, enabling them to phosphorylate target proteins for cell cycle progression.

How are cyclins regulated?

Cyclins are synthesized and degraded in a cyclical pattern corresponding to cell cycle stages.

What happens when cyclins are deregulated?

Deregulation of cyclins can lead to uncontrolled cell division, contributing to cancer.

What are cyclin-dependent kinases (CDKs)?

CDKs are enzymes that, when activated by cyclins, phosphorylate substrates to advance the cell cycle.

Can cyclins function without CDKs?

Cyclins need to bind to CDKs to exert their regulatory role in the cell cycle.

How are cyclin levels controlled?

Cyclin levels are controlled by regulated synthesis and targeted degradation.

How do CDKs function?

CDKs require binding to a cyclin to become active and phosphorylate specific target proteins.

What regulates CDK activity?

CDK activity is regulated by cyclin availability and CDK inhibitors that prevent kinase activation.

How does the cell cycle affect cyclin concentration?

Cyclin concentration varies throughout the cell cycle, peaking when their activity is needed.

Why are CDKs critical for the cell cycle?

CDKs drive cell cycle transitions by phosphorylating key proteins, making them essential for cell division.

What happens if CDKs are inhibited?

Inhibition of CDKs can halt the cell cycle, which is a strategy used in some cancer therapies.

Are all cyclins the same?

Different cyclins are active at various cell cycle stages, each activating specific CDKs.

What is the consequence of cyclin-CDK deregulation?

Deregulation can lead to unchecked cell division and potentially cancer.

What are the implications of cyclin-CDK research?

Understanding cyclin-CDK interactions is crucial for developing cancer treatments targeting cell cycle regulation.

How do cyclins and CDKs interact?

Cyclins bind to CDKs, inducing a conformational change that activates the kinase.

What is the role of CDK inhibitors?

CDK inhibitors bind to CDKs, preventing their activation by cyclins and thus halting cell cycle progression.

Can cyclins activate any CDK?

Cyclins are specific to certain CDKs, ensuring precise control of the cell cycle.

What is the significance of cyclin-CDK complexes?

These complexes are essential for the phosphorylation of substrates that advance the cell cycle.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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