Cell Biology

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Anonymous
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151430
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Cell Biology
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2012-05-01 13:35:56
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  1. Signal transduction
    Message converted from one form to another
  2. Hormones
    Send a general communication throughout the body and are produced by endocrine cells
  3. Paracrine signals
    • Signals diffuse locally through the extracellular fluid, and stay within the region from which they're secreted
    • E.g. Inflammation on wounds
  4. Neuronal signaling
    • Can travel long distance, but signal is picked up by individual cells through their own lines
    • Delivered quickly and specifically to individual target cells through private lines
  5. Synapse
    Junctions where electrical signals are converted to neurotransmitters which diffuse across the gap
  6. Contact-dependent
    • Very short range and done through physical contact of signal molecules and receptors in plasma membrane
    • In embryonic development, contact-dependent signals inhibit neighboring cells from becoming specialied in same way as cell signaling
  7. What happens when a signal molecule binds to its target?
    It can alter the cell's shape, movement, metabolism, and gene expression
  8. What happens in the absence of cell signaling?
    Most animal cells are programmed to kill themselves
  9. Signaling cascade
    • Each target protein is activated by only one type of signal
    • This receptor receives an external signal and generates a new intracellular signal in response
    • This internal signal is passed on until a response is generated
  10. Functions of signaling cascades
    • Transform, or transduce, the signal into a molecular form suitable for passing the signal along or stimulating a response
    • They relay the signal from the point in the cell at which it is received to the point at which the response is produced
    • Amplify the signal received, making it stronger
    • Can distribute the signal to influence several processes in parallel
  11. Speed of a cell's response to a signal
    • If acting on molecule already present in the cell, it will be quick
    • If extracellular signals need changes in gene expression to make new proteins, it will take longer
  12. Which hormones can cross plasma membrane and bind to intracellular receptors?
    • Large hydrophilic hormones cannot
    • Small hydrophobic ones can (steroids)
    • Binding of these small hydrophobic hormones to receptors in the cytosol or nucleus cause a large conformational change in their target proteins, that then either promote or inhibit gene transcription
  13. Which gasses can cross the plasma membrane?
    • NO is a common gas that can diffuse (acts locally to vasodilate smooth muscle - vasodilate)
    • Gases can alter conditions in seconds
  14. What does NO do in the cell?
    • Binds and activates the enzyme guanylyl cyclase
    • Stimulates the formation of cyclic GMP from the nucleotide GTP
    • Cyclic GMP is the next signaling molecule in the chain, which leads to the cell response
    • Local blood-vessel dilation occurs
  15. Viagra
    Blocks the enzyme that degrades cyclic GMP, so the NO signal is maintained
  16. Functions of intracellular signaling pathways
    • Relay signal onward, spreading it
    • Amplify the signal, so few have a great affect
    • Receive other signals from other pathways
    • Distribute signal to other pathways
  17. Signaling proteins act as molecular switches
    • Signal switches from active to inactive state
    • If a signaling pathway is to recover after transmitting a signal and make itself ready to transmit another, every molecular switch must be reset to its original, unstimulated state
    • For every activation mechanism there hase to be an inactivation mechanism
  18. Types of molecular switches
    • Activated or deactivated by phosphorylation
    • Protein kinase (adds phosphate group)
    • Protein phosphatase (removes phosphate)
  19. GTP-binding proteins (G proteins and G-protein-coupled receptors)
    • Switch between active or inactive form depending on if GTP (active) or GDP (inactive) is bound
    • They can hydrolyze the GTP on their own because of their GTPase activity
  20. Ion-channel-coupled receptors
    Opens ion channels and produces an electrical current
  21. G-protein coupled receptors
    • Acive GTP-binding proteins
    • Which then either activates an ezyme or ion channel
  22. Enzyme-coupled receptors (Cell surface receptor proteins)
    • Act as enzymes or work with enzymes inside the cell
    • Switching on this enzymatic activity then generates a hose of additional signals, including small molecules that are released into the cytosol
  23. Cell surface receptors can be acted upon by other molecules
    • The natural ligand that is bound to the receptor can be mimicked by other molecules
    • This ligand will either bind to the ligand-binding site or to another area on the receptor
    • This will result in over-stimulating or blocking the receptor's activity
  24. Nicotine
    • Acts on the neurotransmitter receptor in the central nervous system and muscle cells which are also acted upon by acetylcholine
    • Enhancing effects of epi and norepi
  25. G-protein-coupled receptors
    • Largest family of cell surface receptors
    • Target for drug development (more than half of drugs work on GPCRs)
    • Made of single protein chain
    • Weaves back and forth between the plasma membrane 7 times
  26. G-protein-coupled receptors...
    • Made of 3 subunits
    • Attached by lipids to plasma membrane
    • Unstimulated, GDP is bound to alpha subunit
    • Stimulated, GTP is bound to alpha subunit
  27. Cholera toxin
    • Binds to alpha subunit, and prevents the GTPase activity, therefore it stays activated much longer than it should
    • Causes prolonged release of Cl- and H2O
    • Can be deathly diarrhea and dehydration
  28. G proteins regulate ion channels
    • Heartbeat regulated by 2 sets of nerves (1 speeds and 1 slows)
    • Nerves that signal slowing releases acetylcholine
    • By complex will o pen the K+ channels, and K+ flows out and inhibits the heart cells excitability
  29. Two most common target enzymes for G proteins
    • Adenylyl cyclase (involved in making cyclic AMP)
    • Phospholipase C (inositol triphosphate and diacylglycerol)
  30. Cyclic AMP
    • Activated adenylyl cyclase catalyzes the synthesis of cyclic AMP from ATP
    • Cyclic AMP activates cyclic-AMP-dependent protein kinase (PKA)
    • Activated PKA catalyzes phosphorylation of serines or proteins
    • Adrenaline signal ultimately causes the breakdown of glycogen in skeletal muscles
  31. Inositol phospholipid pathway
    • Triggers increase in Ca++
    • Activated phospholipase C removes the sugar-phosphate head it creates 2 signaling molecules: inositl 1,4,5-triphosphate (IP3) and diacylglycerol (DAG)
    • IP3 remains in cytosol
    • DAG stays in plasma membrane
    • IP3 opens Ca++ channels of ER and Ca++ increases in cytosol
  32. More on inositol phospholipid pathway
    IP3 released into the cytosol will eventually encounter endoplasmic reticulum; there it binds to and opens Ca++ channels that are embedded in the endoplasmic reticulum membrane

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