Mitosis and the Cell Cycle

Overview of Mitosis

Key Concepts

  • Chromatin: Composed of DNA and proteins, contains genes essential for heredity.

  • Chromosomes: Compact structures formed from chromatin, humans have 23 pairs, visible during cell division.

  • Chromatids: Identical halves of a chromosome, held together by a centromere, crucial for accurate DNA distribution during mitosis.

Mitosis Function

  • Mitosis is vital for growth, repair, and reproduction of cells, ensuring genetic consistency.

  • Results in two genetically identical daughter cells, maintaining the organism's genetic integrity.

Genetic Information

  • Genetic material is stored in the nucleus, organized into chromosomes.

  • Chromosomes carry the essential information needed for cell function and heredity.

Phases of Mitosis

Interphase

  • Represents 90-95% of the cell cycle, where the cell grows and performs normal functions.

  • DNA replication occurs, preparing the cell for mitosis.

Mitosis Phases

  • Prophase: Chromosomes condense, and the nuclear envelope remains intact.

  • Metaphase: Chromosomes align at the cell's equatorial plane, preparing for separation.

  • Anaphase: Chromatids are pulled apart to opposite poles of the cell by spindle fibers.

  • Telophase: Two new nuclei form, each containing 46 chromosomes, completing nuclear division.

Cytokinesis

  • Occurs after mitosis, representing about 1% of the cell cycle.

  • The cytoplasm divides, resulting in two separate cells; in plants, a cell plate forms to create a new cell wall.

Reasons for Cell Division

Reproduction

  • Single-celled organisms: Reproduce asexually, producing genetically identical offspring.

  • Multicellular organisms: Reproduce sexually, leading to genetic variation among offspring.

Growth and Repair

  • Multicellular organisms grow by increasing cell numbers through mitosis.

  • Damaged cells are replaced by new cells formed during mitosis, essential for healing.

The Cell Cycle

Phases of the Cell Cycle

  • Interphase: 90-95% of the cycle, where the cell grows and prepares for division.

  • Mitosis: Approximately 5% of the cycle, where the nucleus divides and chromosomes separate.

  • Cytokinesis: About 1% of the cycle, where the cytoplasm divides, resulting in two distinct cells.