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Chapter 9 and 12 bio notes.docx

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BIOL 1103
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Chapter 9Cell CyclesThe increasing size developmental complexity and diversity of functioning of multicellular eukaryotic organisms require strict control of cell divisionMainly results in mature body composed of different subpopulations of cells Whereas most mature cells divide infrequently Cell are actively dividing by the process of mitosis Before dividing most cells enter a period of growth in which they synthesize proteins lipids carbohydrates and replicate there DNA After this growth period the nuclei divide and cytokinesis division of cytoplasm follows partitioning nuclei to each of 2 daughter cells Each daughter nucleus contains a copy of original DNA A period of growth followed by nuclear division and cytokinesiscell cycle91The products of Mitosis are Genetic Duplicates of the Dividing Cell mitosis serves to divide the replicated DNA equallyat a certain stage of cell cycle some cells are needed that are diff from the parent cellsthis cell division is called meiosis produces necessary daughter nuclei have only half the numb of chromosomes as the parental nuclei that began the processmany of genetic traits carried by these daughter nuclei are in diff combinations from those of parent cellcells that are products of meiosis may function as gametes in animals and as spores in plants Chromosomes are nuclear units of genetic info that are divided and distributed by mitotic cell divisionlocated in the cell nucleus and is distributed among linear DNA moleculesthese DNA molecules assist in packaging DNA during cell division and influence individual genes each chromosome is composed of one of these linear DNA molecules along with its associated proteinsmost eukaryotes have 2 copies of each type of chromos in there nuclei diploid or 2n EX humans have 23 chromos for a diploid numb of 46 chroms 2n46 other eukaryotes have only one copy of each type of chromoshaploid n EX bakers yeast can grow as a diploid 2n32and as a haploid n16 other eukaryotes have 34 or more complete sets of chromos setsploidy replication of DNA of each individualchromos creates 2 identical moleculessister chromatids sister chromatids are held together until mitosis separates them placing one in each of the 2 daughter nuclei As a result each daughter nucleus receives the same numb and types of chromos and contains the same genetic info as parent cell entering the divisionthe equal distribution of daughter chroms to each of the 2 cells that result from cell divisionchromosome segregation the precision of chromos replic and segregation in mitotic cell cycle creates a group of cellsclone all cells of a clone are genetically identical92The Mitotic Cell Cyclethe first and longest phase of the mitotic cell cycle is interphase it extends from the end of one mitosis to the beginning of the next mitosis during interphase the cell grows and replicates its DNA in preparation for mitosis M phase and cytokinesisafter interphase mitosis proceeds in five stages Cytokinesis completes cell division by dividing the cytoplasm btw daughter cellsInterphaseDURING all steps of interphase the chromosomes are relatively loose but organized in the nucleus Daughter cell from previous division cycle enters an initial period of cytoplasmic growthDuring initial growth phaseGStagethe cell makes various RNAs proteins 1 and other molecules except nuclear DNA G in G1 stands for gap referring to absence of DNA synthesisIf cell is going to divide DNA replication begins initiating S phase S stands for synthesis meaning DNA synthesisDuring S phase the cell duplicates the chromosomal proteins and DNA and continues the synthesis of other cellular molecules As S phase is completed the cell enter Gphase G2 refers to the second gap 2 during which there is no DNA synthesis During G2 the cell continues to synthesize RNAS and proteins cell continues to grow At end of G2 it is the end of interphase which marks mitosis to begin Gis the only phase of cell cycles that varies in lengthWhether cells divide 1 rapidly or slowly depends on the length of G1Once DNA replic begins mammalian cells take 1012 hrs in S phase 46 hrs thru G2 14 hrs complete mitosis G1 is the stage wen many cells stop dividing The state of division arrest is G0 phase Ex in humans cells of nervous system enter G0 phase once they are fully mature
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