Understanding the Cell Cycle

Overview of the Cell Cycle

• Definition: Time from cell formation to cell division.
• Control: Governed by chemical molecules like cyclins and cyclin-dependent kinases.

Phases of the Cell Cycle

Interphase

• Significance: Occupies the majority of the cell cycle.
• Functions:
  • Cell growth
  • Protein synthesis
  • Execution of cell-specific functions
• Examples:
  • Pancreatic cells make insulin.
  • Neurons produce neurotransmitters.
  • Skin cells (keratinocytes) produce keratin.

Subdivisions of Interphase

1. G1 Phase

   • Cell functions and growth continue.

2. S Phase (Synthesis Phase)

   • Key Event: DNA Replication
   • Importance: Doubles DNA to prepare for mitosis

   DNA Replication Process:

   • DNA is a double helix with complementary base pairs (A-T, C-G).
   • Steps:
     • Unwind and split DNA strands (replication fork formed).
     • Use DNA helicase to unwind strands.
     • Use DNA polymerase to assemble new strands.
     • Result: Two DNA molecules with one old and one new strand (semi-conservative replication).
   • Importance of error correction: Enzymes correct replication errors to prevent mutations.

3. G2 Phase

   • Similar activities as G1.
   • Prepares cell for mitosis.

Mitosis

• Definition: Asexual reproduction, also known as somatic division.
• Result: Division of the nucleus, distributing genetic material.

Phases of Mitosis

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

• Purpose of Mitosis:

  • Growth (embryonic and postnatal)
  • Replacement of old or worn-out cells
  • Healing and repair

• Exceptions: Some cells do not undergo mitosis (ammitotic cells), e.g., cardiac cells, most neurons, osteoblasts.

Cytokinesis

• Definition: Division of the cytoplasm.
• Completion: Results in two daughter cells.

Summary

• The cell cycle is essential for growth, repair, and reproduction of cells.
• Understanding the phases and their functions is crucial to grasp how cells proliferate and maintain body functions.