Exam 1 Study Guide - Mitosis/Meiosis Tuesday 5:10 PM 1 2 3...

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Mitosis/Meiosis Tuesday, February 12, 2008 5:10 PM Mitosis: nuclear division that results in preservation of chromosome number, in human somatic cells are diploid 2N = 46 chromosomes, or 23 chromosome pairs (homologues) (2N, 2c) somatic cell (46 chromosomes, 2 copies of each gene, one from mom, one from dad) 1. Starting cell 2N, 4c a. 2N = 46 chromosomes b. 4c = copy count, number of copies of each gene 2. Prophase a. Chromatin condenses into chromosomes b. Nuclear envelope disappears c. Spindle fibers form 3. Metaphase a. Replicated chromosomes line up along equatorial plane b. Spindle fibers attach to centromere 4. Anapahse a. Replicated chromosomes split and migrate to poles b. movement of chromosomes by assembly/disassembly of spindle 5. Telophase a. Opposite of prophase b. Disolution of chromosomes into chromatin c. Formation of nuclear membrane 6. Cytokinesis a. 2 daughter cells formed b. Each 2N, 2c Def: Monad: unreplicated, 1 chromatid Dyad: replicated, 2 chromosomes Tetrad: paired sister chromosomes, 4 chromatids (homologues) Cell division: consists of nuclear division and cytoplasmic division DNA Replication
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1. Initiation a. Initiator protein starts unwinding of DNA helix (helicase) b. Topoisomerase prevents supercoiling c. RNA primers initiate replication 2. DNA polymerase proceeds in 5'-3' direction 3. Leading strand: one RNA primer, continuous replication 4. Lagging strand a. multiple primers, b. several replication segments c. Okazaki fragments 5. Replicated chromosomes shorten at 5' ends 6. Exonucleases a. remove RNA primers 7. DNA ligase: a. replaces RNA primers with DNA b. links Okazaki fragments 8. Telomerase a. Reverse telomere shortening b. Found in germ cells and cancer cells c. Anti-aging therapy, also attacks cancer cells 9. Importance of Telomeres a. Tip of chromosome shortens with each replication b. When completely eroded cell cannot divide c. Plays role in cell aging i. Shorter the telomere, older the cell Meiosis: reduction division, characteristics of gametes (egg and sperm) results in a haploid chromosome N = 23, chromosomes are unpaired, two step process, beginning with homologous pairs of diploid chromosomes, prior to meiosis DNA replication takes place 1. Starting cell a. 2N, 4c 2. Meiosis I: this is the reduction division, where chromosome number is halved by the separation of the pairs of homologous chromosomes a. Prophase I i. Extended ii. Crossing over occurs b. Metaphase I i. Bivalents line up at equator c. Anaphase I i. Seperation of bivalents into 2 dyads
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d. Telophase I e. Cytokinesis i. 2 cells result ii. Each with half of bivalent pair iii. Each cell is (1N,2c)
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