Biology Chapter 10: Cell Cycle and Cell Division

Introduction

• All organisms start life from a single cell.
• Growth and reproduction are key characteristics of cells.
• Cells reproduce by division, forming daughter cells from parental cells.

10.1 Cell Cycle

• Cell division ensures correct progeny cell formation with genome integrity.
• Cell Cycle: Sequence of events for cell replication and division.

10.1.1 Phases of Cell Cycle

• Interphase and M Phase (Mitosis phase)

  • Interphase: Period between two M phases; preparation for cell division.
    • G1 Phase: Cell growth without DNA replication.
    • S Phase: DNA synthesis; DNA doubles in amount.
    • G2 Phase: Protein synthesis; preparation for mitosis.
  • M Phase: Nuclear (karyokinesis) and cytoplasmic (cytokinesis) division.

• Some cells enter a quiescent stage (G0) where they remain inactive.

10.2 M Phase (Mitosis)

• Involves reorganization of cell components; known as equational division.
• Four stages of nuclear division:
  • Prophase: Chromosomes condense; centrosomes move to poles.
  • Metaphase: Chromosomes align at equatorial plate.
  • Anaphase: Chromatids separate and move to opposite poles.
  • Telophase: Chromosomes decondense at poles; nuclear envelope reforms.

10.2.5 Cytokinesis

• Division of cytoplasm into two daughter cells.
• Animal cells: Cytoplasmic furrow formation.
• Plant cells: Cell plate formation leads to new cell wall.

10.3 Significance of Mitosis

• Results in diploid daughter cells with identical genetic material.
• Essential for growth, repair, and maintenance in multicellular organisms.

10.4 Meiosis

• Specialized cell division reducing chromosome number by half, forming haploid cells.
• Involves two cycles of nuclear division (Meiosis I and II) but one DNA replication.

10.4.1 Meiosis I

• Prophase I: Complex, involves pairing and recombination of homologous chromosomes.
  • Stages: Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis.
  • Crossing over leads to genetic recombination.
• Metaphase I: Bivalents align at equatorial plate.
• Anaphase I: Homologous chromosomes separate.
• Telophase I: Formation of dyad of cells; interkinesis follows.

10.4.2 Meiosis II

• Prophase II: Similar to mitosis; chromosomes condense.
• Metaphase II: Chromosomes align at equator.
• Anaphase II: Sister chromatids separate.
• Telophase II: Ends with the formation of four haploid cells.

10.5 Significance of Meiosis

• Maintains chromosome number across generations in sexually reproducing organisms.
• Increases genetic variability, crucial for evolution.

Summary

• Cell division involves stages from one division to the next, known as the cell cycle.
• Interphase prepares for cell division, followed by mitosis (equational division) or meiosis (reduction division).

Exercises

1. Average cell cycle span for mammalian cells.
2. Difference between cytokinesis and karyokinesis.
3. Describe interphase events.
4. Define G0 phase.
5. Explain why mitosis is called equational division.
6. Identify cell cycle stages for specific events.
7. Describe synapsis, bivalent, and chiasmata.
8. Differences in cytokinesis between plant and animal cells.
9. Examples of equal and unequal meiotic daughter cells.
10. Differences between anaphase of mitosis and meiosis I.
11. Main differences between mitosis and meiosis.
12. Significance of meiosis.
13. Discussion on haploid cells in various organisms.
14. Possibility of mitosis without DNA replication.
15. DNA replication without cell division.
16. Analyze changes in chromosome number and DNA content during cell cycle stages.