Overview
This lecture explains how cells divide, focusing on the cell cycle, chromosome structure, and the steps that lead to the formation of identical daughter cells through mitosis.
The Need for Cell Division
- Multicellular eukaryotic organisms require new cells for growth, development, and repair.
- Examples include growth in young organisms and continuous replacement of cells in adults, such as skin cells.
The Cell Cycle: Main Stages
- The cell cycle is the life cycle of a cell from its creation to division.
- The three main stages are: growth, DNA replication, and mitosis with division (cytokinesis).
Stage 1: Growth
- The cell increases in size and produces more subcellular structures like mitochondria and ribosomes.
Stage 2: DNA Replication
- DNA is duplicated so each new cell gets a full set of genetic material.
Chromosomes Structure and Duplication
- DNA is usually spread out in long strings but condenses into chromosomes during division.
- Chromosomes are coiled-up packets of DNA containing many genes.
- Eukaryotic cells have chromosome pairs (one from each parent); humans have 23 pairs (46 total).
- Each chromosome duplicates and the copy stays attached, forming an X-shape with two identical arms.
Stage 3: Mitosis and Cytokinesis
- Chromosomes line up at the center of the cell.
- Cell fibers attach to each arm and pull them to opposite cell poles.
- Chromosome pairs are split so each side gets an identical set.
- The cell membrane and cytoplasm divide (cytokinesis), forming two identical daughter cells.
Results and Importance
- Each daughter cell has the same DNA as the parent and can enter the cell cycle again.
- This process ensures genetic consistency and supports growth and repair.
Key Terms & Definitions
- Cell Cycle — The series of events from cell formation to its division into two new cells.
- Mitosis — The process of nuclear division resulting in two identical daughter cells.
- Cytokinesis — Division of the cell cytoplasm and membrane to form two separate cells.
- Chromosome — Coiled-up DNA containing genes, condensing during cell division.
- Gene — A section of DNA coding for a specific characteristic.
- Eukaryotic — Cells with a nucleus and other organelles, enclosed by membranes.
Action Items / Next Steps
- Review stages of the cell cycle and chromosome structure.
- Practice related exam-style questions and flashcards, if available.
- Study the difference between mitosis and other forms of cell division.