Chapter 11 RQ

2. 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?

3. 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.

5. 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 

8. 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 

9. 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 

14. 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 

16. 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

19. 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 

20. 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 

22. 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 

24. 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 

26. 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 

27.  The end 

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