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The Cell Cycle.docx

3 Pages

Biological Sciences
Course Code
BISC 101
Tony Williams

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The Cell Cycle: Cell Division and Mitosis  Unicellular organisms produce new organisms through cell division  Sea urchins start off as single cells and then has divided into 4 cells  All multicellular organisms must start as a single cell and then divide  As cells age, get damaged and die you must use cell division to replace them  Cell division is a part of the cell cycle-the entire lifespan of a cell  Parent cells divides into 2 daughter cells  Whole life cycle made up of growth, dna replication and mitosis  Mitosis: need exactly the same number of chromosomes in the daughter cell as the parent cell  Mitotic phase coordinates with the interphase, whole part of the life cycle outside of division itself  Molecular control system- regulation of the cycle  Genome- the entire dna content of the cell  Chromosomes consist of one dna molecule (each 2 m)  Chromosomes are associated with proteins called histones: once they combine they’re called chromatin  The size of the chromosome and the number of genes it expresses aren’t really related  Each eukaryotic cell has a characteristic number of chromosomes in each cell nucleus ( potatoes have 48 chromosomes-humans only have 46)  Genomes of different sizes have different numbers of chromosomes and therefore more dna  Prokaryotic cells have one chromosome- single circular structure  Horsetails have up to 1000 chromosomes  During mitosis the chromosomes has to duplicate when its not dividing its in chromatin form so when they’re not dividing they’re not visible under a microscope  sister chromatids (duplicated chromosomes) are connected by centromeres  centromeres and centrosomes are different  cohesion molecules proteins that link the 2 sister chromatids (only occur in some species)  during mitosis the sister chromosomes have to separate-one set goes into one daughter cell the other set goes into the other one  cytoplasm and organelles must move to opposite sides so division can occue  mitosis is a relatively small part of the cycle  90% of the cells life is spent in interphase  The cell grows throughout interphase  G1 phase: the first gap phase  G2: the second gap phase  Dna synthesis when replication occurs  Mitosis divided into 5 phases: PPMAT Prophase  Mitotic spindles involved in actually separating the two cells  Mitotic spindles fully formed during metaphase  Microtubules -tubulin polymer that make up the cytoskeleton  Microtubule structure is involved so the centrosome is involved  2 types of microtubules : kinetochore and non-kinetochore  Kinetochore: site of attachment where microtubules attach to pull the cell in either direction  Non-kinetochore: can be a part of the spindle structure  The centrosome has to divide first  The spindle then develops  Cell has a complex cytoskeleton structure that must be dismantled  All the tubulin building blocks are used to rebuild the mitotic spindle (starts to occur in prophase) – good example of the dynamic nature of the cell  Spindle microtubules elongate by incorporating tubulin subunits  2 kinetochore microtubules line up the chromosomes in the middle of the cell-metaphase plate; pull the sister chromatids in separate directions  Motor proteins =pacman mechanism 12.9 ); are involved in mechanism to move sister chromatids to either end of cell  Enzyme separase involved  Motor proteins walk the chromatids along the microtubules (act as tracks)  Centrosome end (pole) reels in the chromatids  Interphase isn’t a part of mitosis*  In interphase the centrosomes are already duplicated and the chromatin is too but its so condensed its not really visible  Prophas
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