CELL DIVISION

Cell Structure and Function

• All living organisms are made of cells.

• Life processes occur within cells.

• New cells arise from preexisting cells through cell division.

Types of Cell Division

• Growth: Increase in cell number.

• Repair: Replacing damaged cells.

• Reproduction: Involves mitosis (nucleus division) and cytokinesis (cytoplasm division).

Role of DNA

• DNA directs cell activity by producing enzymes (proteins).

• DNA forms chromosomes, with each organism having a specific number of these.

• Homologous chromosomes code for the same traits.

• In sex cells, only one of each homolog is present.

Interphase

• S phase: DNA replication occurs.

• Trigger proteins accumulate when a cell grows too large for efficient diffusion.

• Most cell life is spent in this phase:

  • DNA is in chromatin form.

  • Centrioles replicate and microtubules form.

  • Nuclear membrane and nucleolus remain intact.

Mitosis Phases

• Prophase:

  • DNA coils into chromosomes.

  • Centrioles move to opposite poles; aster and spindle fibers form.

  • Nuclear membrane begins to break down.

• Metaphase:

  • Nuclear membrane is absent.

  • Replicated chromosomes align at the cell equator.

  • Spindle fibers attach to centromeres.

• Anaphase:

  • Chromatids are separated and pulled to opposite poles.

  • Equal numbers of chromosomes are at each pole.

• Telophase:

  • Spindle fibers break down.

  • Chromosomes uncoil back to chromatin.

  • Cleavage of cytoplasm occurs (cytokinesis).

  • Nuclear membrane and nucleolus re-form.

Post Mitosis

• Resulting in two daughter cells entering Interphase:

  • Cells engage in normal life processes: protein synthesis, digestion, respiration, etc.

  • Go phase: for non-dividing cells (e.g., nerve, red blood cells, most plant cells except meristematic tissue).