Cell Biology: Mitosis and Chromosomes

Cell Division

• Cell division is essential for development, growth, and health.
• Cell death, known as apoptosis, is a programmed process.
• Mitosis is a type of cell division where two identical daughter cells are formed from a single parent cell.

The Cell Cycle

• The cell cycle is the period of growth and division of somatic cells.
• Stages of the cell cycle are:
  • G1: first growth phase.
  • S: DNA synthesis (replication) phase.
  • G2: second growth phase, preparation for cell division
  • M: mitosis (nuclear division).
  • C: cytokinesis (cytoplasm division).

Cell Division in Eukaryotes

• Eukaryotic cells have a nucleus that contains a large and complex genome.
• DNA is organized into linear chromosomes.
• The number of chromosomes varies between species.

Chromosomes in Different Species

• Number of chromosomes in different species:
  • Human: 46
  • Gorilla: 48
  • Mouse: 40
  • Maize: 10
  • Garden pea: 14
  • Drosophila: 8
  • E.coli: 1

Homologous Chromosomes and Sister Chromatids

• Homologous chromosomes are pairs of the same chromosome.
• Each chromosome homologue is composed of two sister chromatids.
• Sister chromatids are held together by a centromere.

Chromosome Makeup

• Chromatin is composed of 40% DNA and 60% protein.
• DNA double helix coils around histone proteins forming a nucleosome.
• The chromatin fibre is further coiled into supercoils.
• Heterochromatin is condensed and does not express genes.
• Euchromatin is uncoiled and expresses genes.

Number of Chromosomes per Cell

• Somatic cells are diploid (2n).
• Diploid cells have two homologues for each chromosome, one maternal and one paternal.
• Gametes are haploid (n).
• Haploid cells have a single copy of each chromosome, either maternal or paternal.

Cell Division in Somatic Cells - Mitosis

• Stages of mitosis:
  • Prophase: formation of the mitotic spindle apparatus.
  • Metaphase: chromosomes align at the metaphase plate.
  • Anaphase: sister chromatids separate and move to opposite poles.
  • Telophase: nuclear envelope reforms, chromosomes decondense, and cytokinesis begins.
  • Cytokinesis: division of the cytoplasm.

Cytokinesis (Animal Cells)

• Cleavage furrow forms, pinching off the two new cells.
• The two daughter cells remain joined by a thin band of cytoplasm.

Cell Growth Checkpoint

• The cell cycle is controlled by checkpoints that ensure proper growth and division.
• The cell cycle checkpoints regulate how often a cell divides.

Test your understanding of the processes involved in mitosis and the structure of chromosomes in eukaryotic cells. This quiz covers key concepts such as DNA replication, homologous chromosomes, and the role of the centromere. Perfect for students studying cell biology!