5.4 Cell Cycle Regulation

4 min read•august 22, 2024

Cell cycle regulation is crucial for maintaining cellular health and preventing uncontrolled growth. This process involves checkpoints, cyclins, and cyclin-dependent kinases that ensure proper DNA replication and cell division.

Understanding cell cycle regulation is key to grasping how cells communicate and respond to their environment. Dysregulation of this process can lead to serious consequences, including cancer, making it a critical area of study in cell biology.

Phases of the Cell Cycle

Interphase and Mitosis

Top images from around the web for Interphase and Mitosis

  • 7.1: Mitosis and the Cell Cycle - Biology LibreTexts View original

    Is this image relevant?

  • The Cell Cycle | Biology for Majors I View original

    Is this image relevant?

  • 7.1: Mitosis and the Cell Cycle - Biology LibreTexts View original

    Is this image relevant?

1 of 3

Top images from around the web for Interphase and Mitosis

  • 7.1: Mitosis and the Cell Cycle - Biology LibreTexts View original

    Is this image relevant?

  • The Cell Cycle | Biology for Majors I View original

    Is this image relevant?

  • 7.1: Mitosis and the Cell Cycle - Biology LibreTexts View original

    Is this image relevant?

1 of 3
  • The cell cycle is divided into two main stages: interphase and mitosis
    • Interphase consists of G1, S, and G2 phases
    • Mitosis is divided into prophase, metaphase, anaphase, and telophase

G1 Phase

  • During G1 phase, the cell undergoes significant growth and prepares for DNA replication
    • Synthesizes proteins and organelles necessary for cell division
    • The restriction point in G1 determines whether the cell will proceed with the cell cycle or enter a resting state (G0)

S and G2 Phases

  • In S phase, DNA replication occurs, resulting in the duplication of the cell's genetic material
    • Each chromosome now consists of two sister chromatids
  • G2 phase involves further cell growth and preparation for mitosis
    • Synthesizes proteins and organelles necessary for cell division

Mitosis and Cytokinesis

  • Mitosis is the process of nuclear division, consisting of four stages:
    • Prophase: chromatin condensation and spindle formation
    • Metaphase: alignment of chromosomes at the metaphase plate
    • Anaphase: separation of sister chromatids
    • Telophase: reformation of nuclear envelopes and decondensation of chromosomes
  • Cytokinesis, the division of the cytoplasm, occurs concurrently with telophase
    • Results in two genetically identical daughter cells

Regulation of Cell Cycle Progression

Cyclins and Cyclin-Dependent Kinases (CDKs)

  • Cyclins and cyclin-dependent kinases (CDKs) are key regulators of cell cycle progression
    • CDKs are a family of protein kinases that phosphorylate specific substrates to drive the cell through the cell cycle
    • Cyclins are regulatory proteins that bind to and activate CDKs
      • The concentration of cyclins oscillates throughout the cell cycle, while CDK levels remain relatively constant
  • Specific cyclin-CDK complexes are active during different phases of the cell cycle
    • Cyclin D-CDK4/6 complexes are important for G1 progression
    • Cyclin B-CDK1 complexes drive the cell into mitosis

Regulation of Cyclin-CDK Activity

  • The activity of cyclin-CDK complexes is regulated by multiple mechanisms:
    • Phosphorylation and dephosphorylation events
    • The presence of CDK inhibitors (CKIs) that can bind to and inactivate cyclin-CDK complexes
  • The ubiquitin-proteasome system plays a crucial role in the degradation of cyclins
    • Allows for the inactivation of cyclin-CDK complexes and the progression of the cell cycle
  • The precise regulation of cyclin-CDK activity ensures the orderly progression of the cell cycle and prevents uncontrolled cell division

Significance of Cell Cycle Checkpoints

Types of Checkpoints

  • Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division
    • Verify that each phase of the cell cycle has been completed correctly before allowing the cell to proceed to the next phase
  • The G1 checkpoint (restriction point) assesses the cell's size, nutrient availability, and presence of growth factors
    • If conditions are favorable, the cell commits to entering the cell cycle; otherwise, it may enter a resting state (G0)
  • The G2/M checkpoint ensures that DNA replication is complete and that any DNA damage has been repaired before the cell enters mitosis
    • Prevents the propagation of genetic errors to daughter cells
  • The spindle assembly checkpoint (SAC) during metaphase ensures that all chromosomes are properly attached to the mitotic spindle before allowing the cell to proceed to anaphase
    • Prevents aneuploidy by ensuring equal separation of sister chromatids

Checkpoint Signaling Pathways

  • Checkpoint signaling pathways, such as the ATM/ATR and p53 pathways, detect DNA damage or other cellular stresses
    • Can halt cell cycle progression to allow for repair or induce apoptosis if the damage is irreparable
  • Defects in checkpoint function can lead to genomic instability
    • Contributes to the development of cancer and other diseases associated with abnormal cell proliferation

Consequences of Cell Cycle Dysregulation

Cancer Development

  • Cancer is a disease characterized by uncontrolled cell division and the ability of cells to invade surrounding tissues and metastasize to distant sites in the body
  • Cell cycle dysregulation is a hallmark of cancer development
    • Mutations in genes that control cell cycle progression, such as proto-oncogenes and tumor suppressor genes, can lead to the formation of cancer cells
  • Proto-oncogenes, such as those encoding cyclins and CDKs, can be mutated or overexpressed in cancer cells
    • Leads to constitutive activation of cell cycle progression and uncontrolled cell division
  • Tumor suppressor genes, such as RB and p53, normally function to inhibit cell cycle progression in response to cellular stresses or DNA damage
    • Mutations or deletions of these genes can result in a loss of cell cycle control and contribute to cancer development

Altered Cell Cycle Kinetics and Genomic Instability

  • Dysregulation of checkpoints can allow cancer cells to continue dividing despite DNA damage or other cellular abnormalities
    • Leads to the accumulation of genetic mutations and increased genomic instability
  • Cancer cells often exhibit changes in cell cycle kinetics
    • Shortened G1 phase and a reduced dependence on growth factors
    • Contributes to their rapid and unchecked proliferation

Targeting Cell Cycle Regulators in Cancer Therapy

  • Targeting cell cycle regulators, such as CDKs, has become an important strategy in the development of cancer therapies
    • Aims to halt the progression of cancer cells and induce apoptosis
  • Examples of targeted therapies include:
    • CDK inhibitors (palbociclib, ribociclib)
    • Checkpoint inhibitors (pembrolizumab, nivolumab)
© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Back
Glossary
Glossary
Next guide