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Mitosis & Cytokinesis Chapter 10
Cell Division In eukaryotes, cell division occurs in two major stages. ¡ The first stage, division of the cell nucleus, is called mitosis. ¡ The second stage, division of the cell cytoplasm, is called cytokinesis. ¡
Why do cells divide by Mitosis? Growth of the organism ¡ Repair of tissue damage ¡ Replacement of old cells ¡ Reproduction of some single celled organisms (Which ones? ) ¡ Amobea Reproducing
Which single celled organisms reproduce by mitosis? The protists or member of the kingdom Protista ¡ They are eukaryotic cells & have a nucleus. Mitosis = division of nucleus. ¡ Bacteria DO NOT divide by mitosis because they don’t have a nucleus. ¡ Bacteria reproduce via binary fission ¡
Cells produced by Mitosis……. Skin ¡ ¡ ¡ Are called daughter cells. Are identical to the original cell Are identical to each other Have the same # of chromosomes Have an identical chromosome makeup
A Duplicated Chromosome centromere one chromatid its sister chromatid One chromosome in the duplicated state
Diploid vs. Haploid Cells ¡ Diploid= l l l A cell that has 2 sets of chromosomes One set came from each parent (mom and dad) Chromosomes come in pairs Humans have 23 pairs of chromosomes for a total of 46 chromosomes per cell Somatic Cells are body cells (all except sperm and egg) and are diploid
Diploid vs. Haploid Cells ¡ Haploid = A cell with 1 set of chromosomes l Gametes or sperm or egg are haploid. l In humans, gametes contain 23 chromosomes l
Stages of Mitotic Cell Division ¡ Prophase = “ 1 st” ¡ Metaphase = “middle” ¡ Anaphase = “apart” ¡ Telophase = “far or separate”
Interphase ¡ ¡ ¡ “Intermission” Normal metabolic (cell) activities Major state of the cell cycle. Cell spends 90% of time here DNA is in the form of chromatin, not coiled into chromosomes The nucleus appears solid. A nucleolus can sometimes be seen.
Late Interphase The cell prepares for mitosis ¡ DNA doubles (replicates) and forms sister chromatids ¡ Centrioles double in animal cells ¡
Prophase ¡ Nuclear membrane disappears ¡ Replicated DNA is condensed ¡ Chromosomes form and can be seen ¡ Spindle fibers start to form
Metaphase ¡ ¡ Chromosomes line up at that equator or middle of the cell The ends of the chromosomes point toward the ends or the poles of the cell.
Spindle & spindle fibers: Pull apart the sister chromatids Spindle fibers
Anaphase Chromosomes move to opposite poles ¡ Centrioles are at the poles in animals ¡ Spindle apparatus is at the pole in a plant ¡
Telophase ¡ Chromosomes gather at opposite ends of the cell and lose their distinct shape. Cell plate or new cells membranes form ¡ Nucleus reappears ¡
Cytokinesis: cytoplasm divides & splits apart
Return to Interphase ¡ New daughter cells each resume the cell cycle in G 1 of interphase. ¡ They will each have a period of growth and normal cell activity before they each divide.
Cytokinesis Mitosis is over, and the spindle is now disassembling. Band of microfilaments at the former spindle equator contracts. The contractions continue and cut the cell in two.
Cytokinesis in Plants ¡ Cell plate In plants, a structure known as the cell plate forms midway between the divided nuclei. Cell wall
Stages of Mitosis
Plant versus Animal Mitosis Plant: ¡ Cell wall from cell plate in telophase ¡ Spindle apparatus Animal: ¡ No cell wall ¡ Cell membrane cytokinesis ¡ Centrioles
Cancerous cells……. . . 1. Divide too many times 2. Divide into more than two cells! ¡ Masses of cells = ¡ “tumors” ¡ benign ¡ malignant