Unformatted text preview: Monday’s Class: RECEPTORS & CELL SIGNALING #2 Chapter 4 Pages: 98-‐130 Chapter 3 Pages: 90-‐121 What you should be able to do by the end of today’s lecture • Understand the chemical classes of signaling factors. • Discuss how the chemistry of signal factors inﬂuences synthesis, transport, and responsiveness at the target cell. • Compare the main classes of receptors and provide examples of situaWons where the receptors regulate physiological processes. • Describe the diversity in receptor-‐enzymes and enzyme-‐linked receptors, and recognize the importance of protein kinase and protein phosphatases. • Discuss how G-‐protein linked receptors induce downstream responses. Types of Cell Signaling INDIRECT SIGNALING Principles of Animal Physiology Figure 4.2, 4.3 Structure of messenger determines signaling mechanism • Why would hydrophobic messengers be diﬀerent from hydrophilic messengers? – Storage? – SecreWon? – Transport? – Receptor? – Eﬀects? • Six main classes of chemicals involved in cellular signaling Transport and Eﬀects of Hydrophobic Messengers Synthesis of pepWde hormones Hydrophilic messengers bind to Transmembrane Receptors When messenger binds receptor, the receptor changes shape, communicaWng (transducing) the signal across the membrane Ligand Chemical messenger that can bind to a speciﬁc receptor Principles of Animal Physiology Figure 4.7 Ligand – Receptor InteracWons • Ligand-‐receptor interacWons are speciﬁc • Only the correctly shaped ligand (natural ligand) can bind to the receptor • Ligand mimics • Agonists – acWvate receptors • Antagonists – block receptors • Many ligand mimics act as drugs or poisons Principles of Animal Physiology Figure 4.12 Ligand-‐Receptor Binding • L + R ↔ L-‐R à response – FormaWon of L-‐R complex causes response – More free ligand (L) or receptors (R) will increase the response • Law of mass acWon • Receptors can become saturated at high L – Response is maximal Receptor number & aﬃnity can vary • More receptors = more likely ligand will bind at any given ligand concentraWon • Can upregulate (e.g. caﬀeine) and downregulate (e.g. heroin) receptor numbers • Receptors can vary in the strength with which they bind ligand InacWvaWon of Ligand-‐Receptor Complex • L-‐R complex must be inacWvated to allow responses to changing condiWons Principles of Animal Physiology Figure 4.16 Signal TransducWon Pathways • Convert signals from one form to another • Four components – Receiver: ligand binding receptor – Transducer: conformaWonal change of the receptor – Ampliﬁer: the signal transducWon pathway increases the number of molecules aﬀected – Responder: something that responds to the signal Types of Receptors (hydrophobic vs. philic messengers?) Focus on signal transducWon pathways most important in regulaWng physiological processes Principles of Animal Physiology Figure 4.18 Intracellular Receptors • Ligand diﬀuses across cell membrane • Binds to receptor in cytoplasm or nucleus • L-‐R complex binds to speciﬁc DNA sequences • Regulates the transcrip6on of target genes • increases or decreases producWon of speciﬁc mRNA Principles of Animal Physiology Figure 4.19 Changes in gene transcripWon Ligand-‐Gated Ion Channels Ligand binds to receptor Receptor changes shape opening a channel Ions move across the membrane ConcentraWon and electrical gradients dictate the direcWon of ion movement • Movement of ions change ion concentraWons which alters the membrane potenWal Principles of Animal Physiology Figure 4.21 •
• Receptor Enzymes (also called enzyme/enzyme-‐linked receptors) • When acWvated by a ligand the catalyWc domain starts a phosphoryla6on cascade • Named based on the reacWon catalyzed Principles of Animal Physiology Figure 4.22 G-‐Protein-‐Coupled Receptors • Transmembrane protein that interacts with intracellular G-‐proteins • G-‐proteins – named for their ability to bind guanosine nucleoWdes • AcWvate second messengers Principles of Animal Physiology Figure 4.27 Cyclic AMP Signaling (First intracellular 2nd messenger discovered) Principles of Animal Physiology Figure 3.27 Next Class: NUTRIENTS & ENERGY METABOLISM Chapter 2 Pages: 39-‐44, 71-‐74 Chapter 2 Pages: 22-‐27, 57-‐60 ...
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- Spring '15
- Receptor antagonist, • movement, Ligand-‐Receptor Complex