Mitosis (For my dear students ^_^ )

For my Biology students, hope the notes below will help you guys somewhat. ^_^ Happy reading! If you still find yourself quite unsure, try cliking on the Mitosis (Flash) link under "For My Students". For further understanding, do try out the quiz, crossword puzzle and interactive tutorials under mitosis. Gambatte and all the best!!


What is (and is not) mitosis?

Mitosis is nuclear division plus cytokinesis, and produces two identical daughter cells during prophase, prometaphase, metaphase, anaphase, and telophase. Interphase is often included in discussions of mitosis, but interphase is technically not part of mitosis, but rather encompasses stages G1, S, and G2 of the cell cycle.

* daughter cells - When a cell divides, it copies its DNA and produces two new daughter cells that have identical DNA


Interphase

The cell is engaged in metabolic activity and performing its prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of which are organizational sites for microtubules.

• G1 - Gap 1 phase, cell enters mitosis, 2N
• S - DNA synthesis occurs, 4N
• G2 - Gap 2 phase, time before metaphase, 4N

M Phase

Prophase
Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle.


















Prometaphase
The nuclear membrane dissolves, marking the beginning of prometaphase. Proteins attach to the centromeres creating the kinetochores. Microtubules attach at the kinetochores and the chromosomes begin moving.





















Metaphase
Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.





















Anaphase
The paired chromosomes separate at the kinetochores and move to opposite sides of the cell. Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.





















Telophase
Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage.















Cytokinesis

In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus. In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells.

** All pictures are taken from HOPES, Huntington's Outreach Project for Education, at Stanford & Mitosis