Cell Division and the Cell Cycle: Study Notes (Ch. 12)

Cell Division and the Cell Cycle

Purpose and Overview of Cell Division

Cell division is a fundamental biological process by which a parent cell divides into two or more daughter cells. It is essential for growth, development, tissue repair, and reproduction in living organisms.

• Purpose of Cell Division: Enables growth, replaces damaged or dead cells, and allows for reproduction in unicellular organisms.

• Types of Cell Division: The two main types are mitosis (produces identical somatic cells) and meiosis (produces gametes for sexual reproduction).

• Result of Mitosis: Two genetically identical daughter cells, each with the same number of chromosomes as the parent cell.

• Result of Meiosis: Four genetically unique daughter cells, each with half the chromosome number of the parent cell.

• Example: Skin cells divide by mitosis to replace cells lost due to injury.

Chromosome Number in Human Cells

Chromosomes are structures within cells that contain DNA and genetic information.

• Human Somatic Cells: Have 46 chromosomes (23 pairs).

• Human Gametes: Have 23 chromosomes (haploid number).

• Additional info: Chromosome number is species-specific; for example, fruit flies have 8 chromosomes.

The Cell Cycle

The cell cycle is the ordered sequence of events that leads to cell division and duplication.

• Main Parts of the Cell Cycle:

  • Interphase: Period of cell growth and DNA replication; includes G1, S, and G2 phases.

  • Mitotic (M) Phase: Includes mitosis and cytokinesis.

• Cell Cycle Duration: Most of the cell's time is spent in interphase.

• Example: Liver cells may spend years in interphase before dividing.

Mitosis: Stages and Events

Mitosis is the process by which a eukaryotic cell separates its duplicated chromosomes into two identical sets.

• Stages of Mitosis:

  1. Prophase: Chromosomes condense, spindle forms.

  2. Metaphase: Chromosomes align at the metaphase plate.

  3. Anaphase: Sister chromatids separate and move to opposite poles.

  4. Telophase: Nuclear envelopes reform, chromosomes decondense.

• Cytokinesis: Division of the cytoplasm, resulting in two separate cells.

• Animal vs. Plant Cytokinesis:

  • Animals: Formation of a cleavage furrow.

  • Plants: Formation of a cell plate.

• Example: Muscle cells divide by mitosis during growth.

Cell Division in Cancer Cells

Cancer cells divide uncontrollably due to mutations in genes that regulate the cell cycle.

• Uncontrolled Division: Leads to tumor formation and can invade other tissues.

• Checkpoint Failure: Cancer cells often bypass cell cycle checkpoints.

• Example: Leukemia is caused by uncontrolled division of white blood cells.

Key Vocabulary

Term	Definition
Chromosome	DNA-containing structure carrying genetic information
Histone	Protein that helps package DNA into chromatin
Daughter Cell	Cell produced from division of a parent cell
Sister Chromatids	Identical copies of a chromosome connected by a centromere
Centromere	Region where sister chromatids are joined
Prophase, Metaphase, Anaphase, Telophase	Stages of mitosis
Spindle	Microtubule structure that separates chromosomes
Kinetochore	Protein structure on chromatids where spindle fibers attach
Metaphase Plate	Imaginary plane where chromosomes align during metaphase
Cleavage Furrow	Indentation that begins cytokinesis in animal cells
Cell Plate	Structure that forms during cytokinesis in plant cells
Benign, Malignant	Types of tumors; benign are non-invasive, malignant invade tissues
Meiosis	Cell division producing gametes with half the chromosome number

Formulas and Equations

• Chromosome Number in Humans: $2n = 46$ (where $n = 23$ is the haploid number)

*Additional info: Expanded definitions and examples provided for clarity and completeness.*