D2.1 Cell and Nuclear Division Lecture Notes

Introduction

• Topic: Cell Division and Mitosis (Standard Level)
• Purpose of Cell Division:
  • Growth: Adding new cells for growth
  • Repair: Repairing tissue and normal cell death
  • Reproduction: Involves cell division
• Cell Theory: New cells arise from existing cells
• Theme D: Continuity and change

Cell Division Process

• Nuclear Division: Division of the nucleus
• Cytokinesis: Division of the cytoplasm
  • Animal Cells:
    • Involves a contractile ring made of actin and myosin
    • Forms a cleavage furrow, leading to cell separation
  • Plant Cells:
    • Formation of a new cell wall
    • Vesicles form new cell membranes
    • Cell plate forms, leading to new cell walls

Equal and Unequal Division

• Equal Division:
  • Parent cell divides into two equal daughter cells
  • Equal cytoplasm and organelles distribution
• Unequal Division:
  • Occurs in gamete production (e.g., oogenesis)
  • Example: Budding in yeast
  • Each cell must receive a nucleus and at least one mitochondrion

Oogenesis

• Process: Produces eggs (oocytes)
• Features:
  • Occurs through meiosis
  • Two rounds of cell division
  • Unequal cytoplasm division
  • Produces one viable oocyte and three polar bodies

Genetic Material Replication

• Importance: Ensures each daughter cell receives a nucleus
• Red Blood Cells: Example of anucleate cells (limited lifespan)

Mitosis vs. Meiosis

• Mitosis:
  • Produces two genetically identical daughter cells (2N, diploid)
  • Ensures continuity of genetic information
• Meiosis:
  • Produces four genetically unique haploid cells (N, haploid)
  • Introduces genetic variation

Chromatin and Chromosomes

• Chromatin: Loose form of DNA
• Chromosomes: Condensed form for division
• Sister Chromatids: Identical arms of a chromosome held by cohesin
• Supercoiling: Process of condensing DNA for mitosis

Spindle Microtubules

• Function: Move chromatids to cell poles
• Cytoskeleton Recycling: Formation of spindle microtubules
• Kinetochore: Microtubule motor for movement

Phases of Mitosis

• Interphase: Not part of mitosis; cell growth and DNA replication
• Prophase:
  • Chromatin condenses into chromosomes
  • Spindle microtubules form, nucleus breaks down
• Metaphase:
  • Chromosomes align at the equator
  • Microtubules attach to centromeres
• Anaphase:
  • Sister chromatids pulled apart
  • Chromatids become individual chromosomes
• Telophase:
  • Chromosomes decondense
  • New nuclear membranes form
  • Simultaneous with cytokinesis

Identifying Mitosis Stages

• Microscope Slide Preparation: Staining and identifying phases
• Interphase: Evenly spread chromatin
• Prophase: Clumped chromosomes
• Metaphase: Chromosomes aligned in the center
• Anaphase: Chromatids pulled apart
• Telophase: Formation of two new nuclei, early cytokinesis