Mitosis and the Cell Cycle

Mitosis and the Cell Cycle

Functions of Cell Division

  • Cell division is a fundamental process integral to the cell cycle, representing the life of a cell from its formation to its own division.

  • Key Functions:

    • (a) Asexual Reproduction: For single-cell organisms (e.g., amoeba), cell division is the primary method of reproduction, creating new organisms.

    • (b) Growth and Development: In multicellular eukaryotes, cell division is essential for:

      • The development of an organism from a fertilized egg into an embryo and then a mature individual.

      • Overall growth of the organism.

    • (c) Tissue Renewal and Repair: For multicellular eukaryotes, cell division is crucial for:

      • Replacing dead or damaged cells.

      • Repairing injured tissues.

      • Maintaining and renewing tissues throughout an organism's life.

Phases of the Cell Cycle

  • The cell cycle is divided into several distinct phases, ensuring proper cell growth and chromosome copying.

  • Interphase (Growth and Metabolism): This accounts for approximately 90%90\% of the cell cycle and includes three subphases:

    • G1\text{1} Phase (First Gap Phase): A period of significant cell growth and metabolic activity. The cell carries out its normal functions and synthesizes new proteins and organelles.

    • S Phase (DNA Synthesis): The most critical event of interphase, where DNA replication (chromosome duplication) occurs. Each chromosome is duplicated, resulting in two identical sister chromatids.

    • G2\text{2} Phase (Second Gap Phase): The cell continues to grow and synthesizes proteins and organelles in preparation for cell division. The cell checks for any errors in DNA replication.

  • M Phase (Mitotic Phase): This relatively short phase includes both mitosis and cytokinesis.

    • Mitosis: The division of the nucleus, resulting in two genetically identical nuclei.

    • Cytokinesis: The division of the cytoplasm, leading to the formation of two separate daughter cells.

Chromosome Duplication (S Phase)

  • Genome: All the DNA within a cell constitutes its genome.

  • Chromosomes: Within a cell, DNA molecules are organized and packaged into structures called chromosomes.

  • Chromosome Number:

    • Somatic Cells (Non-reproductive cells): Contain two sets of chromosomes (diploid).

    • Gametes (Reproductive cells: sperm and eggs): Contain half as many chromosomes as somatic cells (haploid), one set.

  • Duplication Process: In preparation for cell division, two major events occur:

    1. DNA Replication: The cell's entire DNA is replicated.

    2. Chromosome Condensation: The replicated chromosomes condense, becoming compact and visible under a microscope.

  • Duplicated Chromosome Structure: Each duplicated chromosome consists of two identical parts:

    • Sister Chromatids: These are joined copies of the original chromosome, containing identical DNA sequences.

    • Centromere: A constricted, narrow