Understanding the Cell Cycle Process

Sep 6, 2024

The Cell Cycle

Introduction

  • Small molecules like hormones act as messengers in cells.
  • Signals regulate the cell cycle, crucial for cell division and proliferation.
  • New cells replace old ones in the body.

DNA and Chromosomes

  • Each daughter cell needs a complete genome copy.
  • Prokaryotes: one circular DNA molecule.
  • Eukaryotes: multiple linear DNA molecules (chromosomes).
  • Humans have 46 chromosomes (23 from each parent).
  • DNA wrapped around histones forms nucleosomes.
  • Chromatin fibers supercoil for storage and uncoil for replication.

DNA Replication

  • DNA replication results in two identical sister chromatids.
  • Chromatids attached at centromere, separated during cell division.

Stages of the Cell Cycle

  • Interphase (non-dividing phase):
    • G1 phase (first gap): Cell growth.
    • S phase (synthesis): Genome copying.
    • G2 phase (second gap): Preparation for division.
  • M Phase (mitotic phase):
    • Cell divides into two daughter cells.

Regulation of the Cell Cycle

  • Controlled by the cell cycle control system.
  • Regulated by signaling molecules in the cytoplasm.
  • Checkpoints:
    • Ensure proper sequence progression.
    • G1 checkpoint (restriction point): Determines if a cell will divide.
    • S phase checkpoint: Ensures DNA replication accuracy.
    • G2 phase checkpoint: Prepares for mitosis.
    • M phase checkpoint: Manages separation of sister chromatids.

Key Molecules

  • Protein Kinases: Enzymes that activate/deactivate proteins via phosphorylation.
  • Cyclins: Concentration varies, activate kinases.
    • Cyclin-dependent kinases (CDKs): Activated by cyclins.
    • MPF complexes: Allow cell cycle progression.

G1 Phase

  • Cells may enter G0 phase (nondividing state) if no division signal is received.
  • External signals (e.g., growth factors) can reactivate cell cycle.

Density-Dependent Inhibition

  • Cells stop dividing when space is filled.
  • Surface proteins signal when neighboring cell space is occupied.

Cancer and Cell Cycle

  • Cancer cells divide uncontrollably, forming tumors.
  • Disregard normal regulatory signals.
  • Genetic abnormalities lead to cancer.
  • Immune system may recognize and eliminate abnormal cells.
  • Understanding cell cycle regulation is crucial for cancer treatment.