Biology 3201: Cell Division

The Cell Cycle Composed of the following processes: G1 Phase: Cell Growth and metabolic activity (Interphase) S Phase: DNA synthesis and replication (Interphase) G2 Phase: centrioles replicate and cell prepares for division (Interphase) Division of nucleus (mitosis) Division of cytoplasm (cytokinesis)

Interphase Normally the DNA material exists as a mass of thin twisted threads called chromatin. Chromatin is DNA wound around small groups of proteins called histones. At some point during interphase, the chromosomes replicate themselves to become doubled chromosomes. The centrioles also replicate themselves. The centrioles are two cylindrical bodies that lie at right angles to each other near the nucleus. The cell will also build proteins to be used in the cell membrane or as enzymes to be used in chemical reactions that control the duplication of genetic material. In addition, The cell will carry out its normal functions such as growth and maintenance.

Mitosis Mitosis is the first process during cell division and occurs in somatic (body) cells. Mitosis is divided into 4 phases: 1.) Prophase 3.) Anaphase 2.) Metaphase 4.) Telophase At the end of mitosis the same number of chromosomes exist from cell to cell.

* Sister chromatids contain identical DNA 1) Prophase During prophase the genetic material will begin to shorten and contract into thicker rods called chromosomes . Each chromosome is made up of two sister chromatids which are held together by a centromere. * Sister chromatids contain identical DNA The two pairs of centrioles move to opposite ends of the cell, Star shaped structures called asters (made up of microtubules) will extend from each pair of centrioles. Other microtubules will go from pole to pole to form a football shaped structure called the spindle

Prophase ctd The kinetechore is the protein structure on the centromere of the chromosome where the spindle fibers attach during division to pull the chromosomes apart. Chromsomes will begin to move towards the equator The nucleolus and nuclear membrane will disappear.

2) Metaphase During the second phase of mitosis, the spindle fibers attach to the centromere of the replicated chromosomes. They then guide the chromatids to the cell’s equator( middle of the cell) Each of the chromatid has its own spindle fiber attachment leasing from its opposite pole (centriole).

3) Anaphase In anaphase the centromeres split apart and the spindle fibers pull chromatids to opposite poles of the cell. This occurs due to the shortening of the microtubules that make up the spindle fibers.

4) Telophase The final stage of mitosis begins when the chromatids have reached the cells opposite sides (poles). Each chromatid is now a single, non- replicated chromosome. The spindle fibers break down and disappear. The chromosomes unwind and become less visible, and the nucleolus reappears.

Cytokinesis: The cytoplasm separates and two new daughter cells are formed. In animal cells, an indentation of the cell membrane forms and deeps and eventually separates into two cells. In plant cells, a cell wall and membrane form and separate the two cells.

A few definitions: Chromatin: the long fibers that form chromosomes and contain DNA, RNA and various proteins. Sister Chromatid: two structures in a chromosome that are genetically identical which are held together by a centromere Centromere:the point at which two parts of a chromosome join and at which the spindle fibers are attached during mitosis. Spindle fibers: made of microtubules and attatch to the centromere of sister chromatids Centriole: short cylindrical organelle found in animal cells and made up of mictortubules. Parent Cell:the original call that divides to produce two new daughter cells during cell division. Daughter Cell:the two cells produced during mitosis, from the parent cell.

Prophase: the first phase in mitosis Prophase: the first phase in mitosis. When chromosomes condense and can be seen as two chromatids. Metaphase: the second stage of cell division. When chromosomes line up at the cell equator in preparation for separation. Anaphase: A late stage of cell division during which the centromere splits apart and chromosomes move to the poles of the spindle. Telophase: the final stage of cell division in which daughter cell nuclei form around chromosomes at opposite ends of the dividing parent cell.

Specific Curriculum Outcomes: 212-3 213-3 313-2