Cell Cycle Lecture Notes

Introduction to Cell Cycle

• The cell cycle is crucial for cell replication and controlling cell growth.
• Focus on interphase and mitosis.
• Importance of understanding cell cycle regulation via proto-oncogenes, tumor suppressor genes, and DNA repair enzymes.

What is a Cell?

• Basic unit of all living things.
• Eukaryotic cells have three main components:
  • Cell Membrane: Phospholipid bilayer surrounding the cell.
  • Nucleus: Houses genetic material (DNA in the form of chromatin).
  • Cytoplasm: Fluid within the cell.

Phases of the Cell Cycle

Interphase

• The preparation phase before mitosis.
• Composed of three sub-phases:
  1. G1 Phase (Gap 1)
     • Cell growth and preparation for DNA replication.
     • Increase in organelles and synthesis of proteins/enzymes needed for DNA replication.
     • Repair of DNA damage (e.g., thymidine dimers).
     • Most cells spend the majority of their time in this phase.
  2. S Phase (Synthesis)
     • DNA replication occurs, leading to the formation of two identical sets of chromosomes.
     • Uses DNA polymerases (type 1 and type 3) for replication.
     • Chromosome count changes from 2N to 4N (e.g., from 46 to 92 chromosomes).
  3. G2 Phase (Gap 2)
     • Further cell growth and preparation for mitosis.
     • Ensures adequate cytoplasm and organelles for two daughter cells.

Mitosis (M Phase)

• The process of cell division, consisting of several stages:
  1. Prophase
     • Chromatin condenses into chromosomes.
     • Nuclear envelope dissolves.
     • Microtubule organization centers (centrioles) form to assist in chromosome separation.
  2. Metaphase
     • Chromosomes align along the metaphase plate.
     • Polar microtubules attach to kinetochores on the chromosomes.
  3. Anaphase
     • Sister chromatids are pulled apart to opposite poles of the cell.
     • Motor proteins (dynein and kinesin) assist in movement.
  4. Telophase
     • Chromatids reach the poles and begin to de-condense back into chromatin.
     • Nuclear envelopes reform around each set of chromosomes.
     • Cleavage furrow forms to divide the cytoplasm (cytokinesis).

Cell Types and Their Cycle Behavior

• Labile Cells (Proliferative)
  • Constantly undergo cell cycle (e.g., skin cells, blood cells).
• Stable Cells
  • Resting state but can enter cell cycle with a stimulus (e.g., liver and kidney cells).
• Permanent Cells (Amyotic)
  • Do not undergo mitosis (e.g., neurons, cardiac muscle).

Checkpoints in the Cell Cycle

• G1/S Checkpoint: Ensures DNA is undamaged before replication.
• G2/M Checkpoint: Validates DNA replication accuracy.
• M Checkpoint: Confirms correct chromosome alignment before anaphase.

Aging and Telomeres

• Telomeres shorten with each cell division, leading to cell senescence (permanent exit from the cell cycle).

Conclusion

• Understanding the cell cycle is vital for grasping cellular processes and their implications in health and disease.
• Engage with further resources for deeper understanding (e.g., social media platforms and Patreon).