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Cell Cycle and Signaling (Mitosis - cellular division (Evolution of…

- - - - In animal cells, pair of centrioles organize microtubules --> spindle fibers, guide chromosomes during mitosis
- - - - -95% of time is in interphase
        -cell does it's job
        -Synthesizes proteins, enzymes, metabolism
        -Prepares for duplication if triggered
        
        G1 --> 1st gap (growth)
        -non dividing life
        
        S --> DNA synthesis
        -copying/replicating DNA
        -Synthesis phase
        -Dividing cell replicates DNA
        -Must separate DNA copies correctly to daughter cells
        
        G2- more growth, prepares for division
  - - - -Chromatin condenses
        -Centrioles move to opposite poles of cell (animal cells only)
        -Protein fibers cross cell to form mitotic spindle
        -Microtubules coordinate movement of chromosomes
        -Nucleolus disappears nuclear membrane breaks down
  - - - --Spindle fibers attach to centromeres --> kinetochores --> connect centromeres to centrioles
        -chromosomes begin moving
  - - - -Chromosomes align along middle of cell --> metaphase plate
        -Spindle fibers coordinate movement --> ensures chromosomes separate properly
  - - - -Sister chromatids separate at centromere --> move to opposite poles
        -Pulled by proteins walking along microtubules
        -Poles move farther apart --> polar microtubules lengthen
        -Separation of chromatids
        -In anaphase, proteins holding together sister chromatids are inactivated by enzyme separase
        
        Chromosomes movement
        
        -Kinetochores use motor proteins that walk chromosome along microtubule --> microtubules shorten by dismantling at kinetochore end, depolymerization
  - - - -Chromosomes arrive at opposite poles --> daughter nuclei form
        -Chromosomes disperse
        -Spindle fibers disperse
        -Cytokinesis begins --> cell division
        
        Cytokinesis
        
        Animals
        -Constriction belt of actin
        -Microfilaments around equator of cell
        -Cleavage furrow forms --> splits cell in two
        -Like a drawstring bag
        
        Plants
        -Cell plate forms --> vesicles from golgi line up, vesicles fuse to form 2 cell membranes --> new cell wall fuses with existing cellwall
  - - - Singular circular chromsome
        
        No membrane bound organelles
        
        -possible progression of mechanisms intermediate b/w binary fission and mitosis is seen in modern organisms
        
        Dinoflagellates
        
        Diatoms and some yeasts
    - - Protists (dinoflagellates)
        
        Protists (diatoms)
        
        Eukaryotes (yeast)
        
        Eukaryotes (animals)
  - - - 3 major checkpoints
        
        G1/S - Can DNA synthesis begin?
        
        Most critical
        
        -primary decision point --> restriction point
        
        If cell recieves go signal, it divides
        
        Internal signals - Cell growth, cell nutrition
        
        External signals - Growth factors (PDGF)
        
        Density dependent inhbition
        
        Anchorage dependence
        
        Can create cancer
        
        1 more item...
        
        If cell does not recieve signal
        
        G0 --> non dividing working time
        
        G0 go ahead signals
        
        3 more items...
        
        G2/M - Has DNA synthesis been done correctly? commit to Mitosis
        
        Spindle checkpoint - Are all chromosomes attached to spindle?
        
        Control
        
        -Cyclins --> regulatory proteins
        -CDKS --> phoshorylate cellular proteins --> activates or inactivates proteins
        -CDK Cyclin complex --> Triggers passage through different stages of cell cycle
        
        Highly conserved
- - - - Epithelial Cells, blood cells, stem cells
  - - - Brain/nerve cells and muscle cells
        
        highly specialized, never divide
- - - - Common membrane receptors
        
        G-protein coupled receptors --> work with the help of cytoplasmic proteins
        
        Ligand gated ion channels --> open/close in response to binding by signaling molecules (nerve cells and neurotransmitters)
        
        Signaling molecules that are hydrophobic or lipid (steroid hormones) can pass through the bilayer and bind to an intracellular receptor
        
        Receptor tyrosine kinase --> binding of singal molecule to receptors --> dimer --> tyrosine kinase adds a phosphate from an ATP --> initiates a unique cellular response for each activated tyrosine
        
        Can activate multiple cellular responses unlike G-protein
  - - - Second messengers --> CAMP --> diffuse through cytosol--> AMPLIFY signal --> many G-proteins activate the enzyme that makes Camp from ATP
  - - - Transcription factor - Control which genes are turned on