Lecture 31: Cell Reproduction - Chapter 10

Introduction

• Transition from molecular focus to cellular processes
• Comparison of cell division in prokaryotic and eukaryotic cells

Genomes in Prokaryotic and Eukaryotic Cells

Prokaryotic Genome

• DNA is a single, circular closed molecule
• No nucleus; DNA floats in cytoplasm
• Genome: Total genetic information of a cell/organism

Eukaryotic Genome

• Multiple chromosomes; number varies by species
• Humans have 23 different chromosomes (diploid: two sets of chromosomes)
• Haploid: Organisms with one set of chromosomes (e.g., some protists, mosses)
• DNA is wrapped around histone proteins forming nucleosomes, collectively called chromatin
• Chromosomes are linear, not circular

Cell Division

Prokaryotic Cell Division

• Binary Fission
  • Step 1: DNA replication
  • Step 2: Cell elongation and FtsZ protein moves to center
  • Step 3: Chromosomes move to opposite sides; FtsZ forms a ring at cell center
  • Step 4: Septum formation directed by FtsZ
  • Step 5: Cell divides into two identical daughter cells

Eukaryotic Cell Division

• Cell Cycle
  • G1 Phase: Growth and resource accumulation
  • S Phase: DNA synthesis and centrosome replication in animals
  • G2 Phase: Further growth and organelle replication
  • Mitosis: Nuclear division with stages
    • Prophase: Chromosomes condense, nucleus breaks down
    • Prometaphase: Spindle apparatus attaches to sister chromatids at kinetochores
    • Metaphase: Sister chromatids align at cell center
    • Anaphase: Sister chromatids pulled apart
    • Telophase: Chromosomes de-condense, nuclei reform
  • Cytokinesis: Cell divides into two daughter cells, involving cleavage furrow in animals or cell plate in plants

Additional Concepts

• G0 Phase: Resting phase, not part of the cell cycle; cells perform their functions without dividing
• Regulation of Cell Cycle
  • Internal checkpoints:
    • G1: Energy, resources and DNA damage check
    • G2: DNA damage check
    • M: Ensures sister chromatids are correctly attached to spindle
  • External factors: Cells require signals (ligands) to divide, ensuring proper cell density
  • Complex regulation involving numerous proteins

Conclusion

• Lecture 31 concludes with an overview of cell reproduction, to be continued in the next lecture.