Notes on Cell Division and Related Genetics

Cell Division: Key Concepts

  • Big Idea: Understanding cell division is critical for grasping human reproduction and the life processes of various organisms.

Eukaryotic Chromosomes

  • Chromosomes consist of DNA and protein (histones).
  • Prokaryotic cells have a single circular chromosome located in the nucleoid.
  • Eukaryotic cells have multiple linear chromosomes enclosed in a nuclear envelope.

Cell Cycle Overview

  • Phases of the Cell Cycle:

    • Interphase: G1, S, G2 (preparation for mitosis)
    • M Phase: Mitosis and Cytokinesis

  • Interphase Stages:

    • G1 (Gap 1): Growth phase, cell increases in size and prepares for S phase.
    • S (Synthesis): DNA replication occurs, resulting in sister chromatids.
    • G2 (Gap 2): Further growth and preparation for division.

Mitosis Phases

  1. Prophase: Chromatin condenses into visible chromosomes; mitotic spindle forms.
  2. Prometaphase: Nuclear envelope dissolves; spindle fibers attach to kinetochores.
  3. Metaphase: Chromosomes align at the metaphase plate.
  4. Anaphase: Sister chromatids separate and move to opposite poles.
  5. Telophase: Nuclear membranes reform around each set of chromosomes; chromosomes de-condense.

Cytokinesis

  • Division of cytoplasm following mitosis.
  • Animal cells: Form a cleavage furrow.
  • Plant cells: Form a cell plate.

Cell Cycle Regulation

  • Checkpoints control the cell cycle progression:

    1. G1/S Checkpoint: Decides whether to divide.
    2. G2/M Checkpoint: Ensures DNA is replicated.
    3. M Checkpoint: Checks that all chromosomes are attached to the spindle before separation.

  • Cell Cycle Control Proteins:

    • Cyclins and Cyclin-dependent kinases (Cdks) regulate the progression through checkpoints.

Cancer Genetics

  • Proto-oncogenes: Normal genes that can become oncogenes if mutated, leading to uncontrolled cell proliferation.

  • Tumor-suppressor genes: Help prevent uncontrolled cell growth (e.g., p53, Rb). Both copies must be mutated for a cancerous phenotype to occur.

  • p53 Protein: Monitors DNA integrity; initiates repair processes or apoptosis if damage is irreparable.

Binary Fission in Prokaryotes

  • Asexual reproduction process where a single organism divides into two genetically identical entities.
  • Steps include:
    1. DNA Replication: Begins at the origin of replication.
    2. Cell Growth: Cell elongates, preparing for split.
    3. Segregation of DNA: New chromosomes partitioned to opposite ends.
    4. Division: Cell wall forms between two cells, completing the division.

Basic Vocabulary

  • Genome: Total genetic material of an organism.
  • Chromatid: Each half of a replicated chromosome.
  • Kinetochore: Protein structure where spindle fibers attach to chromosomes.
  • Centromere: The region of the chromosome where two sister chromatids are joined.
  • Chromatin: The complex of DNA and proteins (histones) that make up chromosomes.

Study Mnemonic

  • "Go Sally Go! Make Children!" for remembering the order of cell cycle phases:
    • G1, S, G2 (Interphase)
    • Mitosis: PPMAT (Prophase, Prometaphase, Metaphase, Anaphase, Telophase)