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The Cell Cycle.pdf

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Bridget O' Shaughnessy

Biology 1A03 Cell StructureFunction THE CELL CYCLEAll cells arise from preexisting cells by the process of cell divisionFig 111 Two Types of Nuclear Division Occur in Many SpeciesMITOSISMEIOSIS Occurs in somatic cells Occurs only in reproductive cells Produces gametessperms or eggsDaughter cells are genetically identical Daughter cells ova sperm are genetically different from the parent cells contains half of the to parent cell contains the same hereditary information as the parent cell hereditary information IMPORTANCE OF MITOSISMitosisis the division of a somatic parent cell into two genetically identical daughter cells accompanied with cytokinesis the division of the cytoplasm into two daughter cellsensures that each of the daughter cells contain a complete set of chromosomesMitosis and Cytokinesis is responsible for three major events in multicellular organisms1 Growththe body grows by cells continually dividing 2 Repair when you cut yourself cells repairs the skin and heals by dividing through mitosis and cytokinesis 3 Reproduction mitosis followed by cytokinesis is the basis for reproduction by asexually reproducing species 111 MITOSIS AND THE CELL CYCLEChromosomes DNAThreadlike structures contained in the nucleusConsists of a long DNA double helix wrapped around proteins DNA encodes the cells hereditary information or genetic materialGenes are segments of the DNA that codes for a particular protein or ribonucleic acid found in cells By staining the chromosomes with dyes and observing the chromosomes under a light microscope biologists could follow the distribution of this genetic material to daughter cells in mitosisHumans have 46 chromosomes in each celluncondensed uncoiled long and thin chromosomesChromatinfound in interphaseconsist of DNA wrapped around globular proteins called histones compact X shaped form of chromatinChromosomesfound in prophasereplicated DNAhas two sister chromotids held together in the centre by a centromereSingle strand of chromosomesChromatidsReplicated DNA The two chromatids in a chromosome is calledsister chromatids When they are pulled apart in mitosisthey become chromosomesSister chromatids represent exact copies of the same genetic information will get separated into each daughter cell in mitosisEach chromatid contains one long DNA double helixANIMALPLANTS COMPLETE THE CELL CYCLE TO DIVIDE1 INTERPHASEnondividing phase and it represents a very large portion of the Cell Cyclethe cell spends most of its time in the interphasechromosomes are uncondensed uncoiled and are long and thin called chromatineven when dyed the chromosomes are not visible under a light microscope in this phaserequires a lot of energyInterphase consists of three phases1 G1 Phasethe first gap phase First growth and developmentFirst cell growth to ensure that the daughter cells are identical and growing of organelles such as mitochondria2 S Phase Synthesis Phase Chromosomes duplicates DNA synthesisReplicates organelles and manufacture additional cytoplasm Centrioles replicate3 G2 Phase the second gap phase Further growth and developmentSecond cell growth to prepare parent cell for mitosis and cytokinesisWhy do the GAP PHASES existBefore mitosis occurs the parent cell must be large enough and must duplicate organelles and DNA to ensure that the daughter cells are the exact sameWhat is GAP 0 PHASE Gap 0 Phase is the NONDIVIDING STATE or the postmitotic phaseCells in G phase do not go through mitosis These cells will not divide 0 Examples Nerve and muscle cells enter G0 phase once they have fully matured Fully matured nerve and muscle cells do not undergo mitosis will not divide and increase more Therefore when these cells are damaged it can never be replaced However many cells may also trigger its phase from G phase to G phase when more cells are needed When liver 01cells are critically damaged cirrhosis of the liver from drinking alcohol or other incidients the liver cells are triggered back to G phase to regenerate itself and replace the damaged cells When this is complete it goes back to being in G 10phase
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