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Unformatted text preview: C HAPTER HAPTER 12: T 12: T HE HE C C ELL ELL C C YCLE YCLE T HE K EY R OLES IN C ELL D IVISION- V IRCHOW : Where a cell exists, there must have been a preexisting cell, just as the animal arises only from an animal and the plant from a plant-every cell from a cell-cell division: reproduction of cells-unicellular: reproduction entire organism-produce progeny from multi-cellular organisms-enables sexually reproducing organisms to develop from a single cell (fertilized egg, zygote)-repair: replacing cells that die-cell cycle: the life of a cell from the time its formed from a dividing parent cell until its own division of two cells 12.1 C ELL D IVISION R ESULTS IN G ENETICALLY I DENTICAL D AUGHTER C ELLS-most cell division involves the distribution of identical DNA to 2 daughter cells C ELLULAR O RGANIZATION OF THE G ENETIC M ATERIAL-genome: genetic information-eukaryote: number of DNA molecules (long amounts of DNA)-DNA must be copied-DNA molecules are packaged into chromosomes - SOMATIC CELLS : body cells except sex cells-gametes: reproductive cells-chromosomes are made of chromatin: DNA and associated protein molecules D ISTRIBUTION OF C HROMOSOMES D URING E UKARYOTIC C ELL D IVISION-when a cell is not dividing, or as it duplicates its DNA, each chromosome is in the form of a thin chromatin fiber-after DNA duplication, the chromosomes condense-each duplicated chromosome has 2 sister chromatids when chromatin: COHESINS : adhesive protein complexes in which 2 chromatids are initially attached along their lengths (sister chromatid cohesin) when chromosomes: attached by CENTROMERE-part of chromatid on either side of centromere considerd an ARM of the chromatid-mitosis: division of the nucleus which is followed by cytokinesis: division of the cytoplasm-meiosis: produce gametes which yields nonidentical daughter cells that have only one set of chromosomes (occurs only in gonads) 12.2 T HE M ITOTIC P HASE A LTERNATES WITH I NTERPHASE IN THE C ELL C YCLE- F LEMMING : observed chromosomes during mitosis/cytokinesis P HASES OF THE C ELL C YCLE-mitotic (M) phase: mitosis + cytokinesis shortest part of the cell cycle-alternates with INTERPHASE : 90% of cell cycle: cell grows and copies chromosomes in preparation for dividing 1) G1 phase: 2) S phase 3) G2 phase: * All 3 phases: cell grows by producing proteins and organelles * S phase: chromosomes are duplicated if a cells cycle is 1 day long-M phase: less than 1 hour-S phase: 10-12 hours (1/2 cycle)-G1: 5-6 hours-G2: 4-6 hours * G1 MOST VARIABLE in length in different types of cells T HE M ITOTIC D IVISION OF AN A NIMAL C ELL-G2 of Interphase-nuclear envelope bounds the nucleus-nucleus contains one or more nucleoli-2 centrosomes formed by replication of a single centrosome-each centrosome features 2 centrioles-chrosomosomes duplicated during S phase-Prophase-chromatin fibers become more tightly coiled-nucleoli disappear-each duplicated chromosome appears as 2 identical sister chromatids joined together at their centromeres and along their arms by cohesions...
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This note was uploaded on 03/03/2010 for the course BIOG 1101 taught by Professor N/a during the Fall '10 term at Cornell University (Engineering School).
- Fall '10