Lecture Notes: Cell Division and Genetic Material

Introduction to Cell Division

• Importance of cell division for reproduction in single-celled organisms and growth/repair in multicellular organisms.
• Cell division involves both the division of the nucleus and the cytoplasm.
• Genetic information and organelles must be passed to daughter cells.
• Parent Cell: The original cell that divides.
• Daughter Cells: The two new cells produced from division.

Cell Theory

• All cells come from pre-existing cells.

Cell Division in Prokaryotes

• Binary Fission: Division process in prokaryotic cells with a single DNA chromosome.
• DNA is copied, and the cell divides into two daughter cells.

Cell Division in Eukaryotes

• Involves multiple chromosomes.
• Mitosis: Division for somatic cells.
• Meiosis: Division for sex cells (gametes), requires two divisions to produce four daughter cells.

Cytokinesis

• Division of the cytoplasm following nuclear division.
• Animal Cells: Plasma membrane pinches to form a cleavage furrow.
• Plant Cells: Formation of a cell plate due to rigid cell wall.

Genetic Material and Division

• Equal division of cytoplasm and organelles in body tissue cells.
• Unequal division occurs during oogenesis (egg formation), resulting in one large egg and polar bodies.
• Sperm cells: Division of cytoplasm is equal.

Oogenesis Process

• Begins before birth; final development occurs in adulthood.
• Oocyte: Immature egg cell.
• Unequal cytoplasmic division in primary and secondary oocytes.

Importance of DNA Copying

• DNA must be copied before cell division (S phase of the cell cycle).
• Chromatids: Sister chromatids are identical strands of DNA held together by a centromere.

Chromosome Structure

• Nucleosome: DNA wrapped around histone proteins.
• Supercoiling forms compact chromatids.
• Chromatin: DNA associated with histone proteins.

Mitosis

• Division of the nucleus, results in two genetically identical daughter cells.
• Four phases: Prophase, Metaphase, Anaphase, Telophase.

Mitosis Phases

1. Prophase: Chromosomes form, spindle fibers develop, nuclear membrane dissolves.
2. Metaphase: Chromosomes line up at cell equator.
3. Anaphase: Chromatids separate and move to opposite poles.
4. Telophase: Nuclear membranes reform around separated chromatids.

Meiosis

• Occurs in sex cells, reduces chromosome number by half, produces four genetically diverse haploid cells.
• Meiosis I: Chromosome number halved.
• Meiosis II: Sister chromatids separate.

Meiosis Phases

• Similar to mitosis but includes crossing over in Prophase I.
• Crossing Over: Exchange of genetic material between homologous chromosomes.

Genetic Variability

• Crossing Over: Increases genetic diversity.
• Random Orientation: Independent assortment during metaphase.

Errors in Meiosis

• Non-disjunction: Chromosomes fail to separate properly, leading to conditions like Down syndrome.

Summary

• Mitosis and meiosis are essential for growth, reproduction, and genetic diversity.
• Understanding these processes is crucial for comprehending cellular and genetic functions.