CHP 12 Biosignaling (4pp) - Chapter 12 Homework Assignment...

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1 Chapter 12 1 Chapter 12 Homework Assignment • We will not cover the entire chapter. We will cover sections 12.1, 12.3, 12.4, 12.8 and 12.10. • The material in 12.2 (Gated Ion Channels) was covered in CHP 11 in part. • The following problems will be due once we finish the chapter: 2, 3, 9, 10, 11, 13, 17, 19 Chapter 12 Biosignaling Chapter 12 3 Signal Transduction in Biological Systems • Why is signaling necessary for living organisms? • Are there differences between uni- and multicellular organisms? • Are there differences between prokaryotes and eukaryotes? • What are the mechanisms for carrying out signal transduction? Biosignaling Chapter 12 4 Signal Transduction in Biological Systems Biosignaling
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2 Chapter 12 5 Biosignaling Requirements Biosignaling (1) The cell (tissue) must have some kind of receptor for the signal (2) The cell (tissue) must have the metabolic machinery to amplify and respond to the signal Chapter 12 6 Molecular Mechanisms of Signal Transduction Biosignaling Chapter 12 7 [] [ ][ ] L - R L R K L R L - R K d eq = = Ligand Binding is Similar to Ionization Biosignaling Remember, from the Myoglobin/Hemoglobin chapter, the term K d is the dissociation constant and is the inverse of the K eq (or the association constant, K a ) As the K d value decreases in value, the affinity of the ligand for the receptor is increasing. For most binding equilibria in cells (including ligand-receptor interactions), the [L] is much greater than the number of binding sites Therefore, the binding of L to the receptor does not appreciably effect the [L] so it is considered a constant RR L k 1 + k -1 L [ ] L K L [R] L d tot Bound + = = θ Chapter 12 8 Ligand Binding is Similar to Ionization Biosignaling Using Scatchard Analysis we can estimate both the K d and the # of receptor-binding sites. When binding reaches equilibrium, the total number of binding sites (B max ) equals the number of unoccupied sites ([R]) plus the number of occupied sites ([R-L]) B max = [R] + [R-L] [R] = B max –[R-L ] [ ] [ ] [ ] L ) L - R (B L - R L R L - R K max a = = L] [R K 1 B K 1 L L - R d max d = y = b + m x This analysis only works for simple systems
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3 Chapter 12 9 Molecular Mechanisms of Signal Transduction Biosignaling Chapter 12 10 Receptor Enzymes are usually Type I or II integral proteins with two distinct domains: – A Ligand Binding Domain is located on the exterior of the membrane – A Catalytic Domain is located on the interior of the membrane – The two domains are connected by a single transmembrane segment Typically, the catalytic portion is a protein kinase (PK) that phosphorylates target proteins or enzymes once the signal has been received – A typical signal for these receptors are hormones – An example of this type is the Insulin Receptor The phosphorylation target is usually a Tyr in animals and either a Ser or Thr in plants Other Receptor Enzymes may synthesize a secondary messenger such as cyclic GMP (cGMP) Receptor Enzymes Chapter 12 11 • Mobile signals secreted by the endocrine system for distant cell-cell communication
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CHP 12 Biosignaling (4pp) - Chapter 12 Homework Assignment...

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