AP BIOLOGY

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ANIMAL PHYSIOLOGY

CHEMICAL SIGNALS

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Mutations within genes coding for G protein-coupled receptors (GPCRs) can lead to one of two major outcomes-a loss-of-function or a gain-of-function. Loss-of-function mutations prevent signaling in GPCR pathways, even in the presence of signaling molecules. Gain-of-function mutations activate signaling in GPCR pathways, even in the absence of signaling molecules.Which of the following will most likely be found in an individual with a gain-of-function GPCR mutation?
A
Signal transduction pathways that are activated even if ligand-to-receptor binding does not occur
B
Signal transduction pathways that are inactive if ligand-to-receptor binding does not occur
C
Signal transduction pathways that are activated only if ligand-to-receptor binding occurs
D
Signal transduction pathways that are inactive even if ligand-to-receptor binding occurs
Explanation: 

Detailed explanation-1: -For instance, if the gene that creates the receptor protein gets mutated, it could disrupt the entire signal transduction pathway. By contrast, if an enzyme at the end of the signal cascade is subject to mutation, this may result in less of a change to the overall cellular response.

Detailed explanation-2: -Structural alterations provoked by mutations or variations in the genes coding for GPCRs may lead to misfolding, altered plasma membrane expression of the receptor protein and frequently to disease.

Detailed explanation-3: -Inactivating mutations can impair ligand binding, receptor activation/coupling to signaling pathways, or can cause receptor misfolding and consequent impaired expression at the cell membrane.

Detailed explanation-4: -Mutations in GPCR can cause acquired and inherited diseases such as retinitis pigmentosa (RP), hypo-and hyperthyroidism, nephrogenic diabetes insipidus, several fertility disorders, and even carcinomas.

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