1.1 Cell Cycle and Cell Division

Introduction to the Cell Cycle

• The life story of a cell from its birth to division into two daughter cells.
• Fundamental for growth, repair, and reproduction.
• Orchestrated series of events ensuring genetic material is copied perfectly.

The Two Main Phases

1. Interphase: Longest and most active phase; cell grows, carries out functions, and prepares for division.
2. Mitotic Phase (M Phase): Actual cell division; includes mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Interphase: The Preparatory Stage

• G1 (Gap 1) Phase: Cell grows, synthesizes proteins, organelles, and mRNA. High metabolic activity.
• S (Synthesis) Phase: DNA replication occurs; each chromosome consists of two sister chromatids.
• G2 (Gap 2) Phase: Cell continues to grow, synthesizes proteins for mitosis, checks for DNA errors.

Mitosis: The Division of the Nucleus

• Produces two genetically identical daughter nuclei.
• 1. Prophase: Chromosomes condense, nuclear envelope breaks down, spindle fibers form.
• 2. Metaphase: Chromosomes align at the metaphase plate (center of the cell).
• 3. Anaphase: Sister chromatids separate and move to opposite poles.
• 4. Telophase: Chromosomes decondense, nuclear envelope re-forms around each set, cytokinesis begins.

Meiosis: The Reduction Division

• Occurs in sexually reproducing organisms.
• Reduces chromosome number by half (diploid to haploid) to produce four gametes.
• Homologous Chromosomes: Pairs of chromosomes (one from each parent).
• Crossing Over: Exchange of genetic material between homologous chromosomes during Prophase I, creating genetic variation.

Mitosis vs. Meiosis