Questions
APBIO141-031 with labs 10.01 to 10.04 - Video Quiz
Single choice
G protein-coupled receptors are found only in eukaryotes. The ligands that bind to G protein-coupled receptors include a range of compounds including pheromones, hormones and neurotransmitters and range in size all the way from small peptides to large proteins. Which of the following best describes the function of the G protein?
Options
A.The binding of a ligand to the receptor protein activates the G protein. The active G protein binds to its enzyme, causing the replacement of GDP with GTP.
B.The binding of a ligand to the receptor protein causes GTP to replace GDP on the G protein. This activates the G protein, which is now able to bind to its enzyme. The activated enzyme is now able to catalyze the next reaction in the pathway.
C.The binding of a ligand to GDP activates the G protein, which is now able to binding to its enzyme. The activated enzyme is now able to catalyze the next reaction in the pathway.
D.The G protein is a membrane receptor. When the ligand binds to the G protein, GTP replaces GDP. This activates the G protein, which is now able to bind to its enzyme. The activated enzyme is now able to catalyze the next reaction in the pathway.
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Step-by-Step Analysis
To tackle this question, I’ll evaluate what each option says about how G proteins function in GPCR signaling.
Option 1 states that once the ligand binds the receptor, the active G protein binds to its enzyme and this causes GDP to be replaced by GTP. The issue here is the sequence: the exchange of GDP for GTP on the G protein is what activates it, and this exchange is what enables the G protein to interact with its effector. Simpl......Login to view full explanationLog in for full answers
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The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. The figure presents a simplified model of the epinephrine signaling pathway in muscle cells. A plasma membrane is shown with two transmembrane structures, a Beta-2 Adrenergic Receptor and Adenylyl Cyclase. Epinephrine is shown binding to the extracellular surface of the beta-2 adrenergic receptor. Bound to the cytosolic surface of the receptor is a G protein made up of alpha, beta, and gamma subunits. An arrow indicates that G D P that is bound to the alpha subunit of the G protein is now released from the subunit. A successive arrow points to the G protein subunits dissociated from the adrenergic receptor and the alpha subunit dissociated from a complex of the beta and gamma subunits. G T P is shown binding to the alpha subunit. A successive arrow points from the G T P-modified alpha subunit to the cytosolic region of adenylyl cyclase. Adenylyl cyclase intersects an arrow that points from A T P to Cyclic A M P. A series of arrows follows. An arrow from Cyclic A M P points to Protein Kinase A. An arrow from Protein Kinase A points to Phosphorylase Kinase and is paired with a curved arrow pointing from A T P to A D P. An arrow from Phosphorylase Kinase points to Glycogen Phosphorylase and is paired with a curved arrow pointing from A T P to A D P. An arrow from Glycogen Phosphorylase points to an arrow indicating the conversion of Glycogen to Glucose-1-Phosphate. A final arrow points from Glucose-1-Phosphate to Glycolysis. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells Which of the following outcomes will most likely result from the irreversible binding of GDP to the G protein?
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