Cell Division and DNA Structure

Cell Division Purpose

• Cells divide for growth, repair, and reproduction.

DNA Structure

• DNA is a double helix made of nucleotides.
• Each nucleotide consists of a sugar, a phosphate, and a nitrogenous base.
• The bases are adenine (A), thymine (T), guanine (G), and cytosine (C).
• A pairs with T, and G pairs with C.

Cell Cycle Stages

• Interphase: The stage where the cell grows and copies its DNA.
  • G1: The cell grows and carries out normal functions.
  • S: DNA replication occurs.
  • G2: The cell prepares for mitosis.
• Mitosis: The stage where the nucleus divides.
  • Prophase: Chromosomes condense and become visible.
  • Metaphase: Chromosomes line up at the equator of the cell.
  • Anaphase: Sister chromatids separate and move to opposite poles.
  • Telophase: Nuclear membranes form around the chromosomes, and the chromosomes uncoil.
• Cytokinesis: The stage where the cytoplasm divides.

Meiosis Stages

• Meiosis I: The first division, where homologous chromosomes pair up and separate.
  • Prophase I: Chromosomes condense, crossing over occurs.
  • Metaphase I: Homologous chromosome pairs line up at the equator.
  • Anaphase I: Homologous chromosome pairs separate.
  • Telophase I: Two daughter cells form, each with half the number of chromosomes.
• Meiosis II: The second division, where sister chromatids separate.
  • Prophase II: Chromosomes condense again.
  • Metaphase II: Chromosomes line up at the equator.
  • Anaphase II: Sister chromatids separate and move to opposite poles.
  • Telophase II: Four haploid daughter cells form.

Mitosis vs. Meiosis

• Similarities: Both involve DNA replication and division.
• Differences: Mitosis produces two identical diploid daughter cells. Meiosis produces four genetically different haploid daughter cells. Mitosis occurs for growth and repair, while meiosis occurs for gamete production.

Gametogenesis

• Spermatogenesis: The process of producing sperm cells.
  • Occurs in the testes.
  • Each sperm cell has a tail for movement.
• Oogenesis: The process of producing egg cells.
  • Occurs in the ovaries.
  • One egg cell is produced per cycle, along with polar bodies.

Genetic Variation

• Crossing Over: Exchange of genetic material between homologous chromosomes during prophase I.
• Independent Assortment: Random segregation of homologous chromosomes during metaphase I.

Errors in Meiosis

• Chromosome Structure: Deletions, duplications, inversions, translocations.
• Chromosome Number: Aneuploidy (extra or missing chromosomes).

Glossary of Terms

• Make a glossary of important terms for review, including DNA structure, stages of cell division, gametogenesis, genetic variation, and errors in meiosis.