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Wong_Katrina_Block5_MM8 (cell cycle control system - molecules in a cell…

- - - - G1
        
        the cell grows
      - S
        
        chromosome duplication
      - G2
        
        gorws more as it prepares for cell division
    - - prophase
        
        chromosomes condense
        
        nucleoli disappear
        
        duplicated chromosome --> 2 sister chromatids
        
        mitotic spindle forms*
        
        centrosomes part, propelled by the lengthening microtubules between them
      - prometaphase
        
        nuclear envelope fragments
        
        microtubules of spindle invade nuclear area & interact w chromosomes
        
        microtubules extend from each chromosome
        
        each of the 2 chromatids of a chromosome has a kinectochore (@centromere)
        
        some of microtubules attach to the kinectochores-->kinectochore microtubules (jerk chromosomes back and forth)
        
        non kinectochore microtubules interact w those from opposite poles of spindle
      - metaphase
        
        longest stage of mitosis
        
        centrosomes are at opposite ends
        
        chromosomes (centromere) convene on metaphase plate
        
        per chromosome, kinectochores of sister chromatids are attached to kinectocchore microtubules coming from opposite poles
        
        full apparatus of microtubules = spindle because of shape
      - anaphase
        
        =shortest stage of mitosis
        
        begins when 2 sister chromatids of each pair suddenly part, each chromatid --> full fledged chromosome
        
        2 free chromosomes begin moving to opposite ends of the cell, as kinectochore microtubules shorten
        
        cell elongates as nonkinectochore microtubules lengthen
        
        by the end, 2 ends of cell have equivalent & complete collections of chromosomes
      - telophase + cytokinesis
        
        2 daughter nuclei begin to form in the cell
        
        nuclear envelopes arise from fragments of parent's and other parts of endomembrane system
        
        mitosis is complete
        
        chromosomes become less condensed
        
        division of cytoplasm is usually well underway by late telophase, so 2 daughter cells appear shortly after end of mitosis
        
        in animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches cell in two
- - - - chromosomes replicate during S phase but stay uncondensed
      - each replicated chromosome has 2 genetically identical sister chromatids
      - centrosome replicates, forming 2 centrosomes
    - - metaphase 1
        
        pairs of homologous chromosomes (as tetrads) arrange on metaphase plate, w one chromosome per pair facing each pole
        
        both chromatids of a homologue = attached to kinetochore microtubules from one pole; those of the other homologue are attached to microtubules from the opposite pole
      - anaphase 1
        
        chromosomes move to poles, guided by spindle apparatus
        
        sister chromatids stay to the centromere & move as a unit to the same pole
        
        homologous chromosomes, each w 2 sisters, move to opposite poles
      - telophase 1 and cytokinesis
        
        @ beginning of telophase 1, each half of cell has a complete haploid set of chromosomes, but each chromosome = 2 sister chromatids
        
        cytokinesis occus simultaneously w T1, --> 2 haploid daughters
        
        in animal cells, cleavage furrow forms. in plants, cell plate
        
        in some species, chromosomes decondense & nuclear envelope + nucleoli re-form
        
        no chromosome replication occurs between end of meiosis 1 and beginning of meiosis 2, chromosomes are already duplicated
      - prophase 1
        
        takes up 90% of time for meiosis
        
        chromosomes begin to condense
        
        homologous chromosomes loosely pair along their lengths, precisely aligned gene by gene
        
        in crossing over, DNA molecules in nonsister chromatids break at corresponding places, then rejoin too the others DNA
        
        in synapsis, synaptonemal complex (protein structure) forms between homologues, holding em together along their lengths
        
        each tetrad has 1+ chiasmata (criss-crossed regions where crossing over occurred) holds homologues together til anaphase 1
        
        movement of centrosomes, formation of spindle microtubules, break down of nuclear envelope, dispersal of nucleoli
        
        late prophase 1: kinectochores per homologue attach to microtubules from one pole/the other. homologues move --> metaphase plate
    - - metaphase 2
        
        chromosomes are positioned on metaphase plate as in mitosis
        
        2 sister chromatids of each chromosome aren't genetically identical cuz of crossing over
        
        kinectochores of sister chromatids are attached to microtubules extending from opposite poles
      - anaphase 2
        
        centromeres of each chromosome finally separate, the sister chromatid comes apart
        
        sister chromatids of each chromosome now move as 2 individual chromosomes toward opposite poles
      - telophase 2 and cytokinesis
        
        nuclei form, chromosomes begin decondensing, cytokinesis occurs
        
        meiotic division of one parent cell --> 4 daughters, each w a haploid set of unreplicated chromosomes
        
        each of the 4 daughter cells is genetically distinct from other daughter cells and the parent
      - prophase 2
        
        a spindle apparatus forms
        
        in late prophase 2, chromosomes made of 2 chromatids move to metaphase 2 plate
  - - - random orientation of homologous pairs of chromosomes @
        metaphase of meiosis 1
        
        in homologous pairs, each consists of 1 maternal/fraternal, situated on metaphase plate. each may orient a diff direction (50% chance). since each homologous pair is independent of other pairs @ metaphase 1, the first division results in each pair sorting its maternal and prternal homologues into daughter cells independently of every other pair
    - - crossing over --> recombinant chromosomes(derived from both parents)
      - occurs in early prophase 1. 2 nonsisters (maternal and praternal of a homologous pair) are broken at the some place and rejoined to each others DNA.
        
        @ metaphase 2, chromosomes w 1+ recombinant chromatids can be oriented in 2 alternative, non equivalent ways bc their sister chromatids are no longer identical twins. this independent assortment increases variability
    - - random nature of fertilization (each gamete reps 1/8 mil possible chromosome combinations due to independent assortment during meiosis, fusion w a female gamete = 1/64mil)
- - - - protein kinases = enzymes that activate/inactivate other proteins by phosphorylating them, they give the go signal @ G1 and G2.
      - CDK = constant [ ]. to be active, kinase must attach to cyclin, which has fluctuating[ ]. its activity rises and falls depending on its cyclin partner
      - MPF - cyclin-CDK complex, maturation promoting factor, corresponds w [cyclin], triggers cells passage past G2 check point into M phase. when cyclins that accumulate during G2 assoc. w Cdk, MPF initiates mitosis, phosphorylating a variety of proteins.
        
        during anaphase, MPF turns off by destroying its own cyclin. CDK = inactive until it associates w new cyclin molecules
  - - - benign tumor - abnormal cell stays at original site
      - malignant tumor - invasive enough to impair organ function
        
        unusual # of chromosomes
        
        disabled metabolism
        
        lose/destroy attachments to neighboring cells + extracellular matrix, spreads into nearby tissues
        
        can secrete signal molecules that cause blood vessels to grow toward the tumor...travel to other parts of the body metastasis