Critical ThinkingQuestion Many so-called temperature-sensitive mutations have be

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Critical ThinkingQuestion
Many so-called temperature-sensitive mutations have been discoveredin a wide variety of organisms. These are proteins that arenon-functional at higher temperatures, while, at lower temperatures(often just a few degrees lower), they function normally. Forexample, the coloration patterns in Siamese Cats arise from atemperature-sensitive mutation. An enzyme required for thesynthesis of dark pigment is unable to function in areas close tothe body where normal physiological temperatures prevail. However,at the tips of the ears, paws, the tip of the tail and otherextremities where the temperature is slightly lower, the enzymeworks correctly and dark pigment is produced. What is happening atthe molecular level that explains this? Critical ThinkingQuestion
Many so-called temperature-sensitive mutations have been discoveredin a wide variety of organisms. These are proteins that arenon-functional at higher temperatures, while, at lower temperatures(often just a few degrees lower), they function normally. Forexample, the coloration patterns in Siamese Cats arise from atemperature-sensitive mutation. An enzyme required for thesynthesis of dark pigment is unable to function in areas close tothe body where normal physiological temperatures prevail. However,at the tips of the ears, paws, the tip of the tail and otherextremities where the temperature is slightly lower, the enzymeworks correctly and dark pigment is produced. What is happening atthe molecular level that explains this?

Explanation / Answer

One example of this is the case of temperature-sensitivemutations. Often, a single amino acid change within the sequence ofa protein does not change its behavior and interactions with othermolecules, but it does destabilize the structure. In a hightemperature environment, where molecules are moving more quicklyand hitting each other, this results in the protein losing itsstructure and failing to function. In a low temperatureenvironment, however, the protein's structure is stable andfunctions normally. This type of mutation is visible in the coatcoloration of Siamese cats, where a mutation in an enzymeresponsible for pigment production causes it to destabilize andlose function at high temperatures. The protein remains functionalin areas of skin that are colder—legs, ears, tail, andface—and so the cat has dark fur at its extremities.

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