Diagram the FOUR major steps common to signal transduction pathways correct answers 1) BINDING: Extra-cellular signal molecule binds.
2) ACtIVATION: Receptor protein activates.
3) CARRY: Intracellular signaling proteins carry a message.
4) EFFECT: The message reaches the target and causes ...
MMG 409 Exam 2 Learning Objectives(A+ Graded)
Diagram the FOUR major steps common to signal transduction pathways correct answers 1) BINDING: Extra-cellular signal molecule binds.
2) ACtIVATION: Receptor protein activates.
3) CARRY: Intracellular signaling proteins carry a message.
4) EFFECT: The message reaches the target and causes an effect.
Describe the TWO major classes of signaling molecules and how signal characteristics affect receptor location correct answers 1) HYDROPHILIC SIGNALS: Unable to cross the plasma membrane, receptor is a cell surface receptor.
2) SMALL HYDROPHOBIC SIGNALS: Can diffuse across the plasma membrane, receptors are intracellular receptors.
Explain how the receptor binds to a signal and why the Kd is important correct answers Signal (ligand) binds via a simple reversible reaction. Kd (the dissociation constant) is a measure of the affinity of the receptor for its ligand. The lower the Kd, the higher the affinity of the signal for the receptor.
Describe the THREE major classes of cell surface receptors (name, mechanism, example) correct answers 1) ION-GATED COUPLED RECEPTORS: Gated ion channels that a signal can open and close. Example functions include changing the cell membrane potential and cell polarization.
2) G-PROTEIN COUPlED RECEPTORS: Trimeric G-proteins. Example functions include vision and smell.
3) ENZYME COUPLED RECEPTORS: Receptor is a kinase or closely located /coupled to a kinase.
Diagram and describe the 3 main types of molecular on/off switches (name, mechanism, result) correct answers 1) LIGAND BINDING: Allosteric proteins result in a structural change.
2) PHOSPHORYLATION: Phosphate addition, can cause a large change in tertiary structure.
3) GTP-BINDING PROTEINS: Activated or deactivated depending on GTP or GDP, respectively. Changes the activity of the G-protein.
Describe THREE signaling complexes and how they form at activated receptors correct answers 1) SCAFFOLD PROTEINS: Recruited by an activated receptor, bring groups of interacting signaling proteins together. Localizes intracellular proteins to a common location and holds them together.
2) SIGNALING COMPLEX: Built on an activated receptor. Activated receptors can build more than 1 signaling complex that can bind multiple intracellular signaling proteins through, for example, a chain of phosphate binding sites.
3) PI KINASES: Activated by activated receptors. PI kinases phosphorylate PIs (phosphoinositides) that allow signaling complexes to bind and localize.
Define "Molecular Interaction Domains" correct answers Molecular interaction domains mediate interactions between intracellular signaling proteins. Many of the interaction domains are highly conserved and bind to a particular structural motif. The use of modular interaction domains facilitated the evolution of new signaling pathways including SH2, SH3, PTB, and PH domains.
Describe the major characteristics of a G-protein coupled receptor
1) Number of polypeptides
2) Number of transmembrane domains
3) Activation of GPCR creates _____ correct answers 1) Single polypeptide.
2) 7 transmembrane domains (multi-pass transmembrane protein).
3) A binding site for a trimeric G-protein.
Describe the major characteristics of a trimeric G-protein (including names of THREE subunits and which subunit tethered to the plasma membrane and how) correct answers 1) ALPHA SUBUNIT: Two components are G-nucleotide binding site and GTPase domain. Covalently attached lipids anchor in the membrane.
2) BETA SUBUNIT.
3) GAMMA SUBUNIT.
Describe how G-proteins are activated (FIVE steps) correct answers 1) LIGAND BINDS TO RECEPTOR: Signal molecule binds to the GPCR and exposes a binding site for G-
protein.
2) G-PROTEIN BINDS: Receptors act as the GEF and ejects GDP and allows GTP to bind.
3) GTP BINDING ACTIVATES APLHA-SUBUNIT OF G-PROTEIN: Alpha subunit dissociates from the beta/gamma subunit.
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