D2.1 Cell and Nuclear Division Lecture Notes

Introduction

• Focus: Cell division and mitosis (Standard Level)
• Cell Division: Process of creating new cells (copying cells in mitosis)
  • Reasons for cell division:
    • Growth (adding new cells)
    • Tissue repair (injury or normal cell death)
    • Reproduction
• New cells come from existing cells (cell theory)
• Theme D: Continuity and change
  • Cell division processes illustrate both

Cell Division Overview

• Nuclear Division: Dividing everything in the nucleus
• Cytokinesis: Division of the cytoplasm
  • Animal cells: Contractile ring (actin and myosin) forms cleavage furrow
  • Plant cells: New cell wall forms via vesicle fusion, then cell plate

Mitosis

• Parent Cell: Copies its genetic material, divides into daughter cells
• Equal Division: Two equal-sized daughter cells
• Unequal Division (e.g., budding in yeast, oogenesis)
  • Requires each cell receives a nucleus and at least one mitochondrion
• Budding in Yeast: Example of asexual reproduction with unequal division
• Oogenesis: Unequal division producing one viable oocyte and polar bodies

DNA Replication

• Genetic material replicates before division
• Red Blood Cells: Example of anucleate cells (no nucleus)

Continuity and Change

• Mitosis: Continuity
  • Produces two genetically identical diploid daughter cells (2N)
  • Important for conserving genetic information
• Meiosis: Change
  • Produces four genetically unique haploid cells (N)
  • Involves random genetic assortment

Chromosome Structure

• DNA replication results in sister chromatids held by cohesin
• Anaphase: Sister chromatids separated
• Chromosome Condensation: Supercoiling into chromosomes

Mitosis Phases

1. Interphase
   • DNA in chromatin form, doing normal cell functions
   • DNA replication occurs before mitosis
2. Prophase
   • Chromatin condenses into chromosomes, spindle forms, nucleus disintegrates
3. Metaphase
   • Chromosomes line up at cell equator
4. Anaphase
   • Sister chromatids separate and move to poles
5. Telophase
   • Chromosomes decondense into chromatin, new nuclei form
   • Occurs simultaneously with cytokinesis

Cytokinesis

• Division of cytoplasm
  • Animal Cells: Cleavage furrow
  • Plant Cells: Cell plate and new cell wall

Practical Skills

• Microscope Slide Preparation
  • Using onion root tips as they have a lot of mitosis
  • Staining DNA for visibility
• Micrograph Identification
  • Recognize cells in different mitosis stages (interphase, prophase, metaphase, anaphase, telophase)