Detailed Notes on Mitosis and the Cell Cycle

Overview of Mitosis

• Mitosis is the process of cell division that results in genetically identical daughter cells.

Key Reasons for Mitosis

• Tissue Repair/Replacement: Damaged or aged cells are replaced with identical healthy ones.
• Organismal Growth: Multicellular organisms acquire new cells via mitosis.
• Asexual Reproduction: Plants can reproduce through vegetative propagation, which involves mitotic division.
• Development: Zygotes undergo mitosis and differentiate to develop into embryos.

The Cell Cycle

• The cell cycle is an ordered set of events leading to cell division into two daughter cells, roughly divided into:
  • Interphase: The stage between two successive divisions, consisting of three phases:
  • G1 Phase: Cell grows and prepares for DNA replication.
  • S Phase: DNA is synthesized (replicated).
  • G2 Phase: Cell continues to grow and prepares for division.
  • M Phase: The phase where the cell and its contents divide:
  • Mitosis: Nuclear division, where DNA is separated into two identical nuclei.
  • Cytokinesis: Cytoplasmic division that finally splits the cell into two.

Interphase Processes

• Interphase is active and involves various metabolic reactions necessary for cell division:
  • DNA Replication: Occurs in the S phase.
  • Organelle Duplication: Ensuring each daughter cell has organelles.
  • Cell Growth: Cytoplasmic volume must increase before division.
  • Transcription/Translation: Synthesis of key proteins and enzymes.
  • Nutrient Acquisition: Presence of vital cellular materials pre-division.
  • Cellular Respiration: ATP must be produced to drive the division process.

Stages of Mitosis

• Prophase: Chromosomes condense and become visible. Spindle fibers emerge.
• Prometaphase: Nuclear envelope breaks down; kinetochores appear on centromeres.
• Metaphase: Chromosomes align at the metaphase plate, each sister chromatid is attached to spindle fibers from opposite poles.
• Anaphase: Cohesin proteins break down, sister chromatids (now chromosomes) are pulled apart to opposite poles.
• Telophase: Chromosomes reach opposite poles and start to decondense; the nuclear envelope forms around each chromosome set.
• Cytokinesis: Depends on cell type; in animal cells, a cleavage furrow forms, while in plant cells, a cell plate forms to separate the daughter cells.

Checkpoints in the Cell Cycle

• G1 Checkpoint: Checks for nutrients, growth factors, and DNA damage.
• G2 Checkpoint: Assesses cell size and verifies DNA replication.
• M Phase (Metaphase) Checkpoint: Ensures proper attachment of spindle fibers to chromosomes.

Cancer and Tumors

• Tumors arise from uncontrolled cell division, which results from abnormal cell growth and can occur in any tissue.
• Diseases caused by tumors are collectively referred to as cancers.