CELS191 Lecture 14: Eukaryotic Cell Division - Mitosis

Lecture Overview

• Course: CELS191 Molecular Biology & Genetics
• Lecture Focus: Eukaryotic Cell Division - Mitosis
• Professor: Hamish G. Spencer

Lecture Objectives

• Interpret a karyotype.
• Identify the structures of mitosis and summarize the order of events.
• Explain the mechanics and function of mitosis in the context of the cell cycle.

Key Concepts in Genetics

• Genetics affects various fields: Agriculture, Law, Ecology, Sociology, Philosophy, Medicine.

Genetic Material Storage

• Organisms store genetic information through:
  • Viruses: Acellular microbes, may contain linear/circular/segmented chromosomes.
  • Prokaryotic Cells:
  • Bacteria & Archaea: Linear or circular chromosomes; double-stranded DNA.
  • Eukaryotic Cells:
  • Protists, Fungi, Plants, Animals: Linear chromosomes; double-stranded DNA.

Genome Size and Complexity

• Human genome consists of approximately 3,165,000,000 base pairs (haploid set).
• Representation equivalency: A gene of 4000 nucleotides can fill one page; the entire human genome requires 2500 volumes at 50 meters height.

Karyotype

• Definition: An ordered display of chromosomes in a cell, typically prepared from a cell at metaphase.
• Chromosomes: 1 - 22 are autosomes; X & Y are sex chromosomes.
  • Gene: A specific DNA sequence that produces RNA molecules with functions.
  • Homologous Chromosomes: Pairs from each parent containing the same genes.
  • Alleles: Alternative versions of a gene.

Cell Cycle Overview

• Phases:
  1. G1 Phase: Metabolic activity & growth.
  2. S Phase: DNA synthesis.
  3. G2 Phase: Preparation for cell division.
  4. M Phase: Mitosis and cytokinesis.

Mitosis Phases

1. Prophase:

   • Nucleoli disappear; mitotic spindle begins to form.
   • Duplicated chromosomes condense to form sister chromatids.

2. Prometaphase:

   • Nuclear envelope breaks down; chromosomes fully condense.
   • Formation of kinetochores at centromeres.

3. Metaphase:

   • Chromosomes align at the metaphase plate; centrosomes are at opposite poles.
   • Kinetochore microtubules attach to sister chromatids.

4. Anaphase:

   • Sister chromatids separate at centromeres; each becomes a daughter chromosome.

5. Telophase & Cytokinesis:

   • Two daughter nuclei form; chromosomes decondense.
   • Cytoplasm divides: In animal cells, a cleavage furrow forms; in plant cells, a cell plate forms.

Summary of Mitosis

• Mitosis results in two genetically identical daughter cells. Each daughter cell contains one copy of each duplicated chromosome.
• Essential for growth, development, and repair in multicellular organisms.

Exam Preparation Questions

• Identify karyotype elements.
• Outline events in the cell cycle phases.
• List the five mitosis phases in order and illustrate chromosome organization, including mitotic spindle positioning.
• Clarify phases of chromosome separation and alignment during mitosis.
• Determine genetic identity of daughter cells produced by mitosis.