Lecture on Cell Division and Chromosomes

Importance of Cell Division

• Multicellular eukaryotic organisms (humans, plants, walruses) need new cells for:
  • Growth
  • Development
  • Repair
• Young organisms grow in size.
• Older organisms replace lost cells (e.g., skin cells).

The Cell Cycle

• Definition: Life cycle of a cell from creation to division into two new cells.
• Three Main Stages:
  1. Growth
     • Cell grows in size.
     • Increases subcellular structures (e.g., mitochondria, ribosomes).
  2. DNA Replication
     • DNA duplicates to ensure each new cell has a complete set.
  3. Mitosis and Division (Cytokinesis)
     • DNA condenses into chromosomes.
     • Chromosomes contain genes controlling characteristics.

Chromosome Details

• DNA typically spread out; condenses into chromosomes for division.
• Chromosomes:
  • Coiled packets of DNA.
  • Contain a large number of genes.
• Eukaryotic cells have two copies of each chromosome (a pair):
  • One from mother, one from father.
  • Humans: 23 pairs (46 chromosomes total).
• Different species have different chromosome numbers (affects reproduction).

Chromosome Duplication

• Each of 46 chromosomes duplicates, forming X shapes.
• Duplicate attached to original chromosome; each side is an "arm."
• DNA on right arm is the same as the left arm.

Mitosis Process

• Chromosomes line up in cell center.
• Cell fibers attach to chromosome halves, pulling them to opposite poles.
• Chromosomes split into two separate arms.
• All 46 chromosomes undergo this process.

Cytokinesis

• Cell membrane and cytoplasm divide.
• Two identical daughter cells are formed, each with the same DNA as the parent cell.
• Contributes to growth, development, or repair.
• Cells can re-enter the cell cycle.

Additional Resources

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