Lecture 31: Chapter 10 - Cell Reproduction

Introduction

• Focus on cell reproduction, contrasting prokaryotic and eukaryotic cells.
• Genomes in different cell types.

Prokaryotic Cells

• Chromosome Structure: Single circular DNA molecule, floating in cytoplasm.
• Genome: Total genetic information of a cell or organism.
• Binary Fission: Process of cell division in prokaryotes.
  • Steps:
    1. DNA Replication: Chromosome is duplicated.
    2. Cell Elongation: Cell grows larger.
    3. Chromosome Separation: Chromosomes move to opposite sides.
    4. Septum Formation: Wall forms at the center, facilitated by FtsZ protein.
    5. Cell Division: Cell splits into two daughter cells.

Eukaryotic Cells

• Chromosome Structure: Multiple linear chromosomes, wrapped around histone proteins to form nucleosomes and chromatin.
• Diploid vs. Haploid:
  • Diploid: Two sets of chromosomes.
  • Haploid: One set of chromosomes.

Eukaryotic Cell Cycle

• Phases:
  1. G1 (Gap Phase 1): Growth and resource accumulation.
  2. S Phase (Synthesis): DNA replication.
  3. G2 (Gap Phase 2): Organelle replication and further growth.
  4. Mitosis: Nuclear division consisting of several stages:
     • Prophase: Chromosomes condense, nucleus breaks down.
     • Prometaphase: Microtubules attach to sister chromatids.
     • Metaphase: Chromatids align at the cell center.
     • Anaphase: Sister chromatids are pulled apart.
     • Telophase: Chromosomes decondense, nuclei reform.
  5. Cytokinesis: Division of the cell into two daughter cells.
• G0 Phase: Resting phase where cells are not actively dividing.

Cell Cycle Regulation

• Internal Checkpoints:
  1. G1 Checkpoint: Checks for energy, resources, and DNA damage.
  2. G2 Checkpoint: Checks for DNA damage before mitosis.
  3. M Checkpoint: Ensures all chromatids are attached to spindle apparatus.
• External Factors:
  • Cells require external signals to begin division.

Conclusion

• Complex regulation involving many proteins.
• Next lecture will continue with cell reproduction.