Chromosome Structure

• The centromere connects sister chromatids, which are identical DNA molecules tightly wound into chromosomes.
• Chromosome types:
  • Duplicated Chromosome: Contains two sister chromatids.
  • Unduplicated Chromosome: Contains a single chromatid with a tightly wound DNA molecule.

Chromosome Count in Cells

• Diploid Cells (2n):

  • Contain chromosomes in pairs (one from each parent).
  • Example: Human diploid cells have 46 chromosomes (23 pairs).
  • Somatic cells (e.g., brain, liver cells) are typically diploid.

• Haploid Cells (n):

  • Contain one chromosome from each pair, totaling 23 chromosomes in humans.
  • Gametes: Sperm (male) and egg (female) cells are haploid.

Karyotype

• A karyotype shows the complete set of chromosomes in an individual, arranged in pairs.
• Autosomes: 22 pairs of chromosomes that have genes for the same traits.
• Sex Chromosomes: The 23rd pair, which determines sex.
  • X chromosome: Larger with many important genes.
  • Y chromosome: Smaller with fewer genes.
  • XX = female, XY = male.

Cell Division Types

• Mitosis:

  • Involved in growth, tissue repair, and cell replacement.
  • Starts with one diploid parent cell and ends with two diploid daughter cells.
  • Composed of two main processes:
    • Mitosis: Division of the nucleus through four stages:
      • Prophase: Chromatin condenses to form chromosomes; the nuclear envelope breaks down and spindle apparatus forms.
      • Metaphase: Chromosomes align at the cell's equator (metaphase plate).
      • Anaphase: Sister chromatids are pulled apart, creating unduplicated chromosomes.
      • Telophase: Chromosomes revert to chromatin, and the nuclear envelope reforms.
    • Cytokinesis: Division of the cytoplasm, typically starting during anaphase and finished in telophase.

• Cancer:

  • Cancer involves uncontrolled mitotic cell division.
  • Characteristics:
    • Loss of cell cycle control
    • Heritability of mutations
    • Dedifferentiation of cells
    • Loss of contact inhibition; cells continue to divide regardless of surrounding cell density.
    • Angiogenesis: Tumors stimulate blood vessel growth for oxygen/nutrients.
    • Invasiveness and metastasis: Cancer cells invade local tissues and spread to other parts of the body.

Meiosis

• Meiotic Cell Division: Specialized division producing gametes (sperm and egg).
  • Begins with a diploid parent cell and ends with four haploid daughter cells.
  • Consists of two rounds of division:
    • Meiosis I:
      • Stages: Prophase I, Metaphase I, Anaphase I, Telophase I.
    • Meiosis II:
      • Stages: Prophase II, Metaphase II, Anaphase II, Telophase II.
  • Interkinesis: Period between the two meiotic divisions where no DNA replication occurs.

Important Concepts Related to Mitosis and Meiosis

• Mitosis changes the chromosome shape (duplicated to unduplicated) but maintains the chromosome number.
• In meiosis, the reduction of chromosome number from diploid to haploid is essential for gamete formation.

These notes summarizing chromosomal structure and function, types of cell division, and cancer characteristics are key to understanding cell biology. Review and understand these concepts to prepare for your exam!