Cell Division: Mitosis and Meiosis

Study Notes

Cell division is a fundamental process in all living organisms, essential for growth, repair, and reproduction.
Two main types of cell division exist: mitosis and meiosis.
Mitosis produces genetically identical cells for growth and repair of tissues.
Meiosis produces genetically unique cells for sexual reproduction.

Mitosis is a continuous process, but for descriptive purposes, it's divided into four distinct phases: prophase, metaphase, anaphase, and telophase.
Prior to mitosis, the cell goes through interphase, a crucial stage involving DNA replication.
Prophase: Chromatin condenses into visible chromosomes, the nuclear envelope breaks down, and the spindle fibers start to form.
Metaphase: Chromosomes align at the metaphase plate, the center of the cell, ready for separation. Spindle fibers attach to the centromeres of the chromosomes.
Anaphase: Sister chromatids separate and are pulled towards opposite poles of the cell by the shortening spindle fibers.
Telophase: The separated chromosomes reach the poles, the spindle fibers disassemble, and a new nuclear envelope forms around each set of chromosomes.
Cytokinesis follows mitosis, dividing the cytoplasm and creating two separate daughter cells.
The cell cycle is regulated by checkpoints, ensuring accurate DNA replication and distribution.

Meiosis involves two rounds of cell division (meiosis I and meiosis II) to produce four haploid gametes (sperm or egg cells).
Crucially, meiosis reduces the chromosome number by half.

Meiosis I separates homologous chromosomes.
Prophase I: A critical phase involving homologous chromosome pairing (synapsis) and crossing over (genetic recombination). Crossing over leads to genetic variation.
Metaphase I: Homologous pairs align at the metaphase plate.
Anaphase I: Homologous chromosomes separate and move to opposite poles.
Telophase I: Chromosomes arrive at the poles and nuclear envelopes may reform.

Meiosis II is similar to mitosis, separating sister chromatids.
Sister chromatids separate and move to opposite poles.
Cytokinesis follows, resulting in four genetically unique haploid daughter cells (gametes).

Essential for growth and development in multicellular organisms.
Enables tissue repair and regeneration.
Allows for asexual reproduction in some organisms.
Crucial for genetic diversity through sexual reproduction, ensuring variation among offspring.

Precise control over the cell cycle is essential to prevent uncontrolled cell division, which can lead to cancer.
The cell cycle has built-in checkpoints at various stages.
Checkpoints provide crucial quality control to make sure there aren't any mistakes that could lead to disease.

Nutrient availability and cell signaling pathways strongly influence cell division.
DNA damage can also stop cell division and initiate repair mechanisms.
Mutations in crucial cell cycle regulatory genes can lead to uncontrolled cell proliferation, as is often seen in cancerous cells.