Cell Division and Mitosis

Overview of Cell Division

• Definition: Cell division is a fundamental biological process where one cell divides to form two daughter cells.
• Key Functions:
  • Growth and development
  • Tissue renewal
  • Reproduction

Types of Cell Division

• Bacterial Binary Fission: A form of asexual reproduction in bacteria where a single cell splits into two identical cells.

The Cell Cycle

• All cells preparing for division undergo the cell cycle, which includes the following phases:

Interphase

1. G1 Phase (Gap 1):

   • Cells grow and carry out normal functions.
   • Preparation for DNA replication.

2. S Phase (Synthesis):

   • DNA is replicated.
   • Each chromosome now consists of two sister chromatids.
   • Example: If the cell had 4 chromosomes initially, after S phase, it has 8 sister chromatids.

3. G2 Phase (Gap 2):

   • Further growth and preparation for mitosis.
   • Duplicate centrosomes are organized here.

M Phase (Mitotic Phase)

• Includes processes of mitosis and cytokinesis.

• Mitosis involves several stages:

  • Prophase: Chromosomes condense, and the mitotic spindle begins to form.
  • Prometaphase: Nuclear envelope breaks down, and spindle fibers attach to chromosomes.
  • Metaphase: Chromosomes align in the middle of the cell.
  • Anaphase: Sister chromatids are pulled apart toward opposite poles.
  • Telophase: Nuclear envelopes reform around chromosomes.

• Cytokinesis: The final step where the cytoplasm divides to create two separate cells.

  • In animal cells, this is facilitated by a contractile ring made of actin filaments and motor proteins, which help pinch the cell into two.

Centrosomes and Microtubules

• Centrosome: Acts as the microtubule organizing center (MTOC).
  • Duplicates before mitosis to ensure each daughter cell has a centrosome.
• Microtubules:
  • Structure that connects to chromosomes to facilitate their movement during cell division.