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Chapter 11 RQ

Chapter 11 RQ. What is a type of “local signaling” for cells? What is communicated through “long distance” signaling? What is the first stage of cell signaling? What is the general term for any small molecule that binds to a larger one?. Local Regulators

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Chapter 11 RQ

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  1. Chapter 11 RQ • What is a type of “local signaling” for cells? • What is communicated through “long distance” signaling? • What is the first stage of cell signaling? • What is the general term for any small molecule that binds to a larger one?

  2. Local Regulators Paracrine signaling  one cell secretes the signal into extracellular fluid and acts on another cell Synaptic signaling  a nerve cell releases a signal into a synapse, such as another nerve cell or muscle cell Hormones Communicates signals between cells far apart; examples: Plants – ethylene gas which promotes ripening Animals – insulin, a protein which regulates blood glucose levels  1. Categorize chemical signals in terms of the proximity of the communicating cells.

  3. 2. Overview the basic elements of a signaling system of a target cell. 1. Reception  signal binds to a specific cellular protein called a receptor, often at the cell’s surface 2.Transduction  the binding changes the receptor’s conformation which initiates a process of converting the signal into a specific cellular response (which may have 1 or more steps) 3. Cellular response  can be almost any cellular activity, such as activation of an enzyme or altered gene expression 

  4. 3. Describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal transduction system. • Ligand  term for a small molecule that binds to another larger molecule • The signal molecule is complementary to a specific region of the receptor protein  the alteration in receptor conformation or shape can lead to the activation of the receptor which enables it to interact with other cellular molecules 

  5. 4. Compare and contrast G-protein-linked receptors, tyrosine-kinase receptors, and ligand-gated ion channels. G-protein linked  single polypeptide chain threaded over membrane - interacts with a variety of proteins - hosts metabolic and developmental processes Tyrosine-kinase  characterized by an extracellular ligand-binding domain and enzyme activity - ligand binding causes aggregation of 2 receptor units which activates the kinase activity Ion channels  protein pores in the membrane that open or close in response to ligand binding, allowing or blocking the flow of specific ions 

  6. 5. Describe how phosphorylation propagates signal information. • Some phosphorylation results in activation of the target protein (increasing catalytic activity) • Some result in inactivation • Protein kinases act on other proteins (sometimes enzymes) and attach the phosphate group to serine or threonine residues • Used in signal paths in the cytoplasm of the cell 

  7. 6. Describe how cAMP (cyclic AMP) is formed and how it propagates signal information. • Ligand binds to receptor • Receptor conformation changes; G-protein complex is activated • Active G-protein activates the enzyme adenylyl cyclase which is associated with the cytoplasmic side of the plasma membrane • Adenylyl cyclase converts ATP to cAMP • cAMP binds to and activates a cytoplasmic enzyme protein kinase A • Protein kinase A propagates the message by phosphorylating various other proteins that lead to the cellular response

  8. 7. Describe how the cytoplasmic concentration of Ca 2+ can be altered and how this increased pool of Ca 2+ is involved with signal transduction. • Altered in two ways: 1. Ligand binding to a Ca2+ ion-gated channel 2. Activation of the inositol triphosphate (IP3) signaling pathway - ligand binds, conformation change - IP3 is created and binds to Ca2+ ion-gated channels 

  9. Continued… • Ca2+ affects the signal transduction 1. Directly  affects the activity or function of target proteins 2. Indirectly  binds to a relay protein which in turn alters the activity of enzymes 

  10. 8. Describe how the signal information is transduced into cellular responses in the cytoplasm and in the nucleus. • Cytoplasm  affect on the function or activity of the proteins, including: - rearrangement of the cytoskeleton - open/close of an ion channel - key points in metabolic pathways • Nucleus  affect on synthesis of new proteins by turning on/off genes - transcription/translation - gene expression 

  11. 9. Describe how signal amplification is accomplished in target cells. • The making of second messengers like cAMP provides some amplification - this is increased when it is linked to a phosphorylation cascade - ex: few epinephrine molecules are needed to result in millions of glucose molecules released from glycogen in the liver 

  12. 10. Describe how target cells discriminate among signals and how the same signal can elicit multiple cellular responses. • Discriminate  like the enzyme, it is specific to certain cells and receptors • Multiple responses  depending on the cell it binds to, the responses can vary hugely ex: epinephrine on liver vs cardiac - liver  induces breakdown of glycogen - heart  stimulates contraction 

  13.  The end 

  14. “Mothers of teenagers know why some animals eat their young.” -unknown

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