Lecture Notes: The Cell Cycle of an Animal Cell

Overview

• The cell cycle of an animal cell involves the stages of the cell's life cycle.
• Main stages: Interphase and M stage (Mitosis).
• Focus of this lecture: Interphase.

Interphase

• Purpose: Prepares the cell for cell division.
• Duration: Longest stage, occupying 90% of the cell cycle.
• Sub-processes: Comprised of three phases – G1, S, and G2.

G1 Phase (Growth Phase)

• Entry: Begins after cell division.
• Activities:
  • Chromosome unwinding into euchromatin.
  • RNA production for protein synthesis.
  • Synthesis of organelles and cell machinery.
  • Cell grows and doubles in size.
• Checkpoint: Restriction point at the end, determines if cell proceeds to divide.
  • Options:
    • Conditions favorable: Progress to S phase.
    • Conditions unfavorable: Enter G0 phase (resting phase).
      • E.g., skin, intestinal, and stomach cells divide frequently, while nerve cells remain in G0.

S Phase (Replication Phase)

• Main Activity: DNA replication.
• Details:
  • Focused on replicating 46 chromosomes.
  • Original and replicated chromosomes joined at the centromere.
  • Produces chromatids; a total of 92 chromatids at the end.

G2 Phase (Preparation for Mitosis)

• Purpose: Ensures preparation for mitosis.
• Activities:
  • Continued synthesis of proteins and organelles.
  • Verification of chromosome replication.
• Checkpoint:
  • Checks concentration of Mitosis Promoting Factor (MPF).
  • High MPF levels trigger transition to M stage.

M Stage - Preview

• Next Lecture: Focus on Mitosis.
• Phases:
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Cytokinesis: Process of cell division.

Summary

• Interphase is crucial for cell preparation before division.
• Consists of G1 (growth), S (DNA replication), and G2 (preparation for mitosis).