Understanding Cell Division and the Role of Chromosomes
Introduction
- Multicellular Eukaryotic Organisms:
- Require constant supply of new cells.
- Essential for growth, development, and repair.
- Necessary for young organisms to grow and older organisms to replace lost cells (e.g., skin cells).
The Cell Cycle
- Definition: The life cycle of a cell from creation to division.
- Main Stages:
- Growth
- DNA Replication
- Mitosis and Division (Cytokinesis)
Stages of the Cell Cycle
1. Growth
- Cell Growth:
- Increase in size.
- Increase in number of sub-cellular structures like mitochondria and ribosomes.
2. DNA Replication
- DNA Duplication:
- Ensures each new cell receives a full set of DNA.
Chromosome Formation
- DNA in Non-Dividing Cells:
- DNA exists as long strings.
- DNA in Dividing Cells:
- Condenses into chromosomes (coiled packets of DNA).
- Gene Control:
- Chromosomes contain genes that control characteristics (e.g., eye color).
- Chromosome Pairs:
- Eukaryotic cells have pairs of chromosomes, one from each parent.
- Humans: 23 pairs (46 total chromosomes).
- Species have different chromosome numbers, affecting reproduction.
Preparing for Division
- Chromosome Duplication:
- Each chromosome duplicates and stays attached, forming an X shape.
- Each half is referred to as an arm.
- DNA is identical on both arms of the X.
3. Mitosis
- Alignment:
- Chromosomes line up in the center of the cell.
- Cell fibers attach to each chromosome arm.
- Separation:
- Fibers pull chromosome arms to opposite sides (poles) of the cell.
- Chromosomes break into two separate arms.
Final Stage: Cytokinesis
- Cell Division:
- Cell membrane and cytoplasm divide.
- Forms two daughter cells.
- Daughter Cells:
- Each has identical DNA.
- Identical to each other and the parent cell.
- Can enter the cell cycle for growth, development, or repair.
Conclusion
- Cell Division: Important for organismal growth and repair.
- Encouragement to engage with further content.
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