Cell Cycle and Cell Division Notes

Cellular Reproduction

  • Cell division is essential for: new offspring, repair, growth/development, and gamete formation.
  • Asexual reproduction: offspring are genetic copies.
  • Sexual reproduction: fusion of gametes.

Prokaryotic Cell Division

  • Binary fission: how prokaryotes reproduce.
  • Circular DNA replicates, copies separate into daughter cells.

Eukaryotic Genetic Material

  • DNA housed in membrane-bound nucleus.
  • Chromatin: relaxed DNA during interphase.
  • Chromosomes: compact DNA during cell division.
  • Humans have 23 homologous chromosome pairs with similar genetic information.

Cell Cycle

  • Sequence of cell growth and division.
  • Includes interphase (growth) and mitosis (division).

Interphase

  • G1 (growth phase): cell grows, produces proteins/organelles.
  • S (synthesis phase): chromosomes duplicate via replication. Sister chromatids held by centromere.
  • G2 (growth phase): cell grows, produces proteins/organelles.

Mitotic Phase

  • Mitosis: chromosomes divide (5 stages).
  • Cytokinesis: cytoplasm divides.
  • Mitosis yields two identical daughter cells, important for repair, replacement, growth.

Mitosis Stages

  • Prophase: chromosomes condense, centrioles move, spindle fibers form.
  • Prometaphase: nuclear envelope fragments, chromosomes move, spindle fibers form.
  • Metaphase: chromosomes align at metaphase plate, centrioles at poles, spindle fibers bind.
  • Anaphase: centromeres split, sister chromatids separate and move to opposite poles.
  • Telophase: chromosomes decondense, nuclear envelope reforms, spindle fibers break down, cytokinesis starts.

Cytokinesis

  • Division of cytoplasm and physically separates daughter cells.
  • Animal cells: cleavage furrow.
  • Plant cells: cell plate.

Cell Cycle Control System

  • Checkpoints ensure error-free division; errors halt progression.
  • G1 checkpoint: continue cycle or enter G0 (nondividing).
  • G2 checkpoint: continue only if DNA replicated properly.
  • M checkpoint: continue only if chromosomes attached to spindle fibers.
  • Loss of control can lead to cancer (uncontrolled growth).