I Chromosomes A Literally translates as Colored Body

I. Chromosomes A. Literally translates as “Colored Body” B. B. DNA: Uncoiled, it is too thin to be seen with light microscope.

C. Chromatin: DNA + Proteins 1. Histones – proteins DNA wraps around (like spools of thread) 2. Nucleosome – one histone wrapped with DNA.

Twisted Staircase to “X”

Kinetochore One nucleosome DNA histone core Fig. 9. 9, p. 156 -157

I. Chromosomes D. The “X” is a condensed, duplicated chromosome. 1. The “X” consists of two sister chromatids (exact copies of one another) 2. Connected at centromere (constriction where microtubules can connect)

D. The “X” is a condensed, duplicated chromosome. 3. Kinetochore – the protein disc where SF actually attach

I. Chromosomes Sister Chromatids, Centromere, Copies of DNA, Chromosome(s)

II. Mitosis A. Purpose: To generate Two identical (Twin) nuclei. To genetically CLONE a cell. B. Where in Body? 1. Somatic Cell: Body cells (all except sperm and eggs, which are sex cells). 2. To generate DIPLOID cells (two copies of each chromosome, 2 n).

II. Mitosis Stages: A. Prophase: 1. Cell often loses shape (due to cytoskeleton disassemblage) 2. Nuclear membrane disintegrates. 3. DNA (sister chromatids) begins condensing. 4. Centrioles (animal cells) duplicate and move to poles of cell. 5. Spindle fibers (made of microtubule subunits) begin to assemble from each pole.

Prophase

II. Mitosis B. Metaphase: 1. Cell elongates as spindle microtubules overlap in middle. 2. Spindle fibers align chromosomes at equator. 3. “Meta” translates as middle

Metaphase

II. Mitosis C. Anaphase 1. Microtubules attached to centromeres shorten and pull sister chromatids apart. 2. Other microtubules grow past one another to further elongate cell. 3. Chromosomes move to poles.

Anaphase

Fig. 9. 10, p. 157

II. Mitosis D. Telophase: (largely opposite of prophase) 1. Nuclear envelop reforms. 2. Chromsomes uncondense. 3. Spindle fibers disassemble. 4. Centrioles move from poles.

Telophase

II. Mitosis Final Results: Initial 46 chromosomes 1 cell Final

Cell Prior to Mitosis

Label

III. Cell Cycle A. Interphase: 1. G 1 (Gap 1): Normal cell growth. 2. S phase: Synthesis, DNA replicated 3. G 2 (Gap 2): Cell prepares for division. B. Mitosis: Equal distribution of chromosomes into two nuclei. C. Cytokinesis: Division of cytoplasm to make two cells.

IV. Cancer (Add to Notes) What is Cancer? Body cells undergoing excessive mitosis/cell division.

Fig. 9. 3, p. 151

Where in cell cycle? Interphase: Mitosis:

IV. Cytokinesis A. Cell leaves mitosis as 1 cell with 2 nuclei! B. Cytokinesis is division of cytoplasm 1. Animal Cells: Cleavage furrow forms as cell constricts. 2. Plant Cells: Cell plate forms as two cells divide cytoplasm.

cell wall former spindle equator light micrograph and transmission electron micrograph showing cell plate formation in a dividing plant cell vesicles converging cell plate Fig. 9. 6, p. 154

Mitosis is over, and the spindle is now disassembling. Just beneath the plasma membrane, a band of microfilaments at the former spindle equator contracts, so that its diameter shrinks all around the cell. The contractions continue and cut the cell in two. Fig. 9. 7, p. 154