Mitosis and Cytokinesis Overview

Stages of Mitosis

Interphase Overview

  • G1 Phase (Gap 1)

    • Initial stage where the cell grows and produces organelles needed for division.

    • Known as the longest phase of interphase.

  • S Phase (Synthesis)

    • Focuses on replication of DNA.

    • Chromosomes duplicate, resulting in sister chromatids connected by the centromere.

  • G2 Phase (Gap 2)

    • Final preparation phase before mitosis, ensuring all structures necessary for cell division are complete.

Prophase

  • Centrosomes begin to divide, initiating the formation of mitotic spindles.

  • Centrosome and Centrioles: Organelles involved in the production of microtubules specific for mitosis.

  • Microtubules grow and form what’s called asters.

  • Chromosomes condense and become visible as sister chromatids.

  • End of prophase is marked by the nuclear envelope disappearing.

Metaphase

  • Chromosomes align in the middle of the cell at the metaphase plate.

  • Kinetochore, a protein at the centromere, binds the microtubules from opposite sides of the spindle.

  • Each sister chromatid faces opposite poles of the spindle, preparing for separation.

  • This stage is critical for karyotyping to detect chromosomal abnormalities (e.g., Down syndrome).

Anaphase

  • Separation of Sister Chromatids: Once aligned, cohesin proteins holding chromatids together are cleaved by the enzyme separase.

  • Chromatids are pulled to opposite poles by the mitotic spindle microtubules, leading to an increase in the chromosome count as they separate.

Telophase

  • Chromatids reach the poles, and a new nuclear envelope begins to form around each set of separated chromatids, now individual chromosomes.

  • The chromosomes begin to unpack into chromatin form.

  • Mitotic spindles begin to disassemble.

  • Cytokinesis typically overlaps with telophase, leading to the final separation of the daughter cells.

Cytokinesis in Animal Cells

  • A cleavage furrow forms due to a contractile ring of microfilaments, which pinches the cell membrane to create two daughter cells.

Cytokinesis in Plant Cells

  • Vesicles gather at the center of the cell, forming a cell plate that eventually develops into a new cell wall separating the two daughter cells.

Differences Between Mitosis and Bacterial Division (Binary Fission)

  • Bacteria do not undergo mitosis due to lack of nucleus; division occurs via binary fission.

  • In binary fission, the circular chromosome replicates, and the cell elongates before dividing, resulting in two genetically identical daughter cells.

Summary of Key Points

  • Understand the stages of mitosis (prophase, metaphase, anaphase, telophase) and their significance in cell division.

  • Know the differences between animal and plant cell cytokinesis.

  • Recognize the importance of coordinating mitotic events with cellular structures, like the centrosome and kinetochore, to ensure accurate chromosome separation.

  • Familiarize with the implications of chromosomal abnormalities and their detection through karyotyping.