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Chapter 12:CharacterProkaryotesEukaryotesGenomeSingle, circular or linearMultiple, linear chromosomesNucleusNoneYesCell divisionBinary fissionMitosisCell cycleNoneInterphase (G1, S, G2), mitosisCell cycle- the life of a cell from the time it first forms from a dividing parent cell from the time it first forms from a dividing parent call until its own division into 2 daughter cellsMost cell division (except meiosis) involves distribution of identical DNA to 2 daughter cellsGenome- a cell’s endowment of DNADNA is packaged into chromosomesChromosomes- one very long linear DNA molecule associated with many proteinsDNA carries genes, the units of info that specify an organism’s inherited traitsChromatin- entire complex of DNA and proteins that serve as building material for chromosomesWhen not dividing, chromosomes are in form of thin, long chromatin fiberAfter replication, chromosomes condense: chromatin fibers become densely coiled and folded, making chromosomes shorter and thickSomatic cells (nonreproductive cells/ body cells)- have two sets of chromosomes (diploid, 2n)46 chromosome, 2 sets of 23 in humansGametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells (haploid, 1n)1 set of 23 in humansSister chromatids- joined copies of original chromosomeEach contain identical DNA moleculesAttached to each other by cohesinsAttachment known as sister chromatid cohesionCentromere- region containing specific DNA sequences where the chromatid is attached most closely to its sister chromatidPart of chromatid on either side of centromere is known as an armSister chromatids:12.2:Mitosis- division of genetic material in nucleusCytokinesis- division of cytoplasmZygote- fertilized eggCell cycle can be divided into:Mitotic (M) phase- mitosis and cytokinesis, shortest part of cell cycleInterphase (90%)- a cell that is about to divide grows and copies its chromosomes in preparation for cell divisionG1 phase (first gap)- most variable in time, cell doing job in organismS phase- only times chromosomes are duplicatedG2 phase (second gap)During these subphases, a cell that will eventually divide grows by producing proteins and cytoplasmic organellesThe Mitotic Spindle:First begins to form during prophaseMade up of microtubules and proteinsMicrotubules of cytoskeleton disassemble to supply material to construct mitotic spindlePolymerizes through subunits of protein Tubulin, Depolymerizes by losing subunitsAssembly of spindle microtubules start at centrosomeCentrosome- a subcellular region containing material that functions through cell cycle to organize the cell’s microtubulesPair of centrioles are located at center of centrosomes. These centrioles are nonessential to cell divisionDuring interphase, centrosome duplicates to form 2 centrosomes that remain together near nucleusThe centrosomes move apart during prophase and prometaphase as spindle microtubules grow out of themAt end of prometaphase, there is a centrosome at each pole of the spindle, on opposite ends of the cellAster- a radical array of short microtubules extending from each centrosomeKinetochores- a structure of proteins associated with specific sections of chromosomal DNA at each centromereEach sister chromatid of duplicated chromosomes have a kinetochoreFace in opposite directionsSome spindle microtubules attach to kinetochores during prometaphaseAttachment to a kinetochore makes chromosome move toward whichever pole the kinetochore is onSince there are kinetochores on both sides, there is no net movementMetaphase plate- term used to describe the plate boundary between the spindle’s two poles that centromeres of duplicated chromosomes are found on during metaphasePolar microtubules- microtubules not attached to kinetochoresStart elongating and by metaphase are overlapping and interacting with other nonkinetechore microtubules from opposite poles of spindleBy metaphase, microtubules of asters have grown and are in contact with plasma membrane completing the spindleDuring anaphase, separase cleaves the cohesins holding together the sister chromatids of each chromosomeOnce chromatids separate into chromosomes, they move toward opposite ends of cellIn a dividing animal cell, nonkinetochore microtubules are responsible for elongating the whole cell during anaphaseNonkinetochore microtubules overlap during metaphaseRegion of overlap reduced as motor proteins walk microtubules away from one anotherCell elongates as microtubules push apart since spindle poles are pushed apartMicrotubules lengthen through addition of tubulin to overlapping ends and continue to overlapAt end of anaphase, duplicate groups of chromosomes arrive at opposite ends of an elongated parent cellNuclei reform during telophaseCytokinesis in animal cells:Usually begins during anaphase or telophaseOccurs through cleavage in animal cellsCleavage furrow- a shallow groove in cell surface near old metaphase plateContractilve ring of actin microfilaments located on cytoplasmic side of furrowActin molecules interact with myosin and cause ring to contractCauses cleavage furrow to deepen until parent cell is pinched into 2 separated cellsCytokinesis in plant cells:During telophase, vesicles from Golgi move along microtubules to middle of cell and coalesce to form a cell plateCell wall materials carried in vesicles collect in cell plate to make it growCell plate enlarges until its surrounding membrane fuses with plasma membraneResults in 2 daughter cells with their own plasma membraneContent of cell plate form a cell wall between the 2 daughter cellsBinary fission in bacteria (prokaryotes)Binary fission- a type of reproduction in which cell grows to double its size and then divides to form 2 cells, asexual production of single celled eukaryotesInvolves mitosis in eukaryotes, does not in prokaryotesBacteria genes are carried on a bacterial chromosome that consists of circular DNA and associated proteinsOrigin of replication- location at which DNA of bacterial chromosome begins to replicate in order to form 2 originsAs chromosome replicates, one origin moves toward opposite ends of cellCell elongates as chromosome is replicatingAfter replication, a bacterium reaches about 2x its initial sizePlasma membrane pinches inward and divides parent cell into 2 daughter cellsA protein resembling actin functions in bacterial chromosomal movementA protein related to tubulin helps pinch plasma membrane inwardEvolution of Mitosis:Mitosis believed to have


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UGA BIOL 1107 - Chapter 12

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