The Cell Cycle and Cell Division Notes

The Cell Cycle and Cell Division Notes

Chapter 7 Overview

  • Key Concepts: 7.1 Asexual & Sexual Reproduction 7.2 Asexual Reproduction Results in Genetically Identical Cells 7.3 Sexual Reproduction via Meiosis & Genetic Diversity 7.4 Errors in Cell Division Affect Chromosome Numbers 7.5 Regulation of the Cell Cycle and Cell Death

7.1 Asexual and Sexual Reproduction

  • Cell Division:
  • One cell divides into two.
  • Types: Asymmetrical (e.g., yeasts) and Symmetrical (e.g., bacteria, protists).
  • Asexual Reproduction:
  • Offspring are clones; variations due to mutations.
  • Prokaryotes reproduce via binary fission; eukaryotes via mitosis.
  • Sexual Reproduction:
  • Exclusive to eukaryotes; involves gametes formed by meiosis, leading to genetic variety.

7.2 Asexual Reproduction Mechanisms

  • Four key events during cell division:
  1. Cell Division Signals
  2. DNA Replication
  3. DNA Segregation
  4. Cytokinesis
  • Binary Fission Process for Prokaryotes: Initiation of replication then segregation along the cytoskeleton.

7.3 Meiosis and Genetic Diversity

  • Meiosis I & II:
  • Meiosis I: Halves chromosome numbers; homologous chromosomes pair.
  • Meiosis II: Similar to mitosis; sister chromatids separate, resulting in four haploid cells.
  • Crossing Over: Increases genetic diversity during prophase I.

7.4 Errors in Cell Division

  • Nondisjunction: Homologs fail to separate, resulting in aneuploidy (abnormal chromosome numbers).
  • Consequences: Miscarriages, developmental issues (e.g., Down syndrome).
  • Polyploidy: Extra sets of chromosomes; often in plants and fungi, rarely beneficial in animals.

7.5 Regulation of the Cell Cycle and Cell Death

  • Prokaryotes rely on nutrient levels to regulate the cell cycle.
  • Eukaryotes: Signals for division are internal; growth factors influence it.
  • Cell Cycle Phases:
  • G1: Normal functions, cells can arrest in G0.
  • S Phase: DNA replication.
  • G2: Preparation for mitosis.
  • M Phase: Mitosis and cytokinesis.
  • Checkpoints in Eukaryotes: R point (G1/S transition) regulates progression based on internal signals like CDKs and cyclins.
  • Apoptosis vs. Necrosis:
  • Necrosis involves cell swelling and bursting; apoptosis is programmed cell death, eliminating damaged or unneeded cells without inflaming surrounding tissues.