Overview of Cell Cycle and Division

Sep 10, 2024

Cell Cycle and Cell Division Lecture

Introduction

  • Definition of Cell Cycle: Self-regulated sequence of events for cell growth and division into two daughter cells.
  • Continuous process: Cells divide and daughter cells begin the cycle again.

Major Phases of the Cell Cycle

Interphase

  • Definition: Period between two successive cell divisions.
  • Function: Cell growth and replication of genetic material.
  • Sub-phases of Interphase:
    • G1 Phase (Gap 1):
      • Occurs immediately after cell division.
      • Cell growth and nutrient accumulation.
      • Preparation of DNA replication machinery.
      • Critical for successful cell division; defects can lead to cancer.
    • S Phase (Synthesis):
      • DNA replication occurs, doubling genetic material.
      • Formation of chromatids for each chromosome.
      • Checkpoints for DNA integrity and repairs.
    • G2 Phase (Gap 2):
      • Follows DNA replication.
      • Continued cell growth and organelle reorganization.
      • Centrioles formation crucial for cell division.

M Phase (Mitotic Phase)

  • Definition: Period of actual cell division.
  • Includes nuclear and cytoplasmic division.
  • Stages of Mitosis:
    • Prophase:
      • Condensation of genetic material into visible chromosomes.
      • Disintegration of nuclear envelope.
      • Movement of microtubules and centrioles.
    • Metaphase:
      • Chromosomes align at the cell equator.
      • Ideal for karyotyping.
    • Anaphase:
      • Separation of sister chromatids to opposite poles.
    • Telophase:
      • Cytoplasmic division.
      • Reconstitution of nuclear envelope.

Importance of Mitosis

  • Increases cell number rapidly (e.g., blood cells).
  • Growth and development of organisms and organs.
  • Repair and replacement of worn-out tissues.
  • Maintains genetic consistency—daughter cells identical to parent cell.

Meiosis

  • Occurs only in germ cells (sperm and oocytes).
  • Involves two phases: Meiosis I and Meiosis II.
    • Meiosis I: Separation of homologous chromosomes, reducing chromosome number to haploid (23 chromosomes).
    • Meiosis II: Similar to mitosis but with haploid cells.
  • Purpose:
    • Achieves haploidy for fertilization, restoring diploid state in offspring.
    • Genetic variation through crossing over.

Cells in G0 Phase

  • Description: Cells that have exited the cycle, lost division capacity.
  • Termed as "quiescent" stage or terminal differentiation.
  • Examples: Mature red blood cells, skeletal muscle cells, most neurons, many cardiac muscle cells, osteocytes.

Conclusion

  • The lecture covered the cell cycle's role in growth, division, and maintaining genetic integrity.
  • Importance of mitosis and meiosis in cell proliferation, organism development, and genetic consistency and variation.