A conditional mutation is a mutation that has wild-type (or less severe) phenoty
ID: 99393 • Letter: A
Question
A conditional mutation is a mutation that has wild-type (or less severe) phenotype under certain "permissive" environmental conditions and a mutant phenotype under certain "restrictive" conditions. For example, there is an enzyme that catalyzes the production of the pigment responsible for dark fur color in Siamese cats and Himalayan rabbits. The enzyme is heat sensitive, meaning that it does not function at higher temperatures. Rabbits raised at 5°C are all black. If raised at 20°C, they are white with black paws, ears, and noses. When raised at 35°C, they are all white. Similarly, a snowshoe hare exhibits seasonal fur coloration. Hares living in 5°C are all white to provide camouflage in the snow; hares living at 35°C have brown fur to provide camouflage in their forest habitat. 2. For the Siamese cat and the Himalayan rabbit, which of the following best represents an activity curve for this enzyme: a or b? Explain why you think so. a. Supposing that the snowshoe rabbit had a conditional mutation resulting in seasonal fur coloration, which of the following curves could represents an activity curve for this enzyme: a or b? Explain why you think so. (Please note, this is not how it really works for snowshoe rabbits. The coloration ina snowshoe hare is due to molting, based on day length rather than temperature. You do not need to fit that into the question. I am forcing the snowshoe hare example to fit here.) b. Fast Fast Slow Slow 5 10 15 20 25 30 35 40 45 50 5 10 15 20 25 30 35 40 45 50 Temperature (°C) Temperature (°C) a. b.Explanation / Answer
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a) best curve is "a". This is because the enzyme shows maximum activity at lower temperatures i.e. around 5°C and reduces as the temperature increases. Hence the rate of reaction too would be max around 5°C and would decrease with increasing temperature.
b) In case of a conditional mutation in the snowshoe rabbit, graph "b" would represent it enzyme activity. This mutant at lower temperature would have wild type phenotype i.e. white fur which developed due to absence of any pigment. This means that the enzyme activity (which is responsible for computation) is low. It would rise with temperature resulting in brown fur at around 35°C. So, the rate of reaction also would be low at lower temperatures gradually increasing with temperature with a peak at 35°C (as shown in graph "b").
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a) non-competetive inhibitor binds to a site different from the active site, called and allosteric site. This binding induces a conformational change in the enzyme resulting in an abnormal shape of the active site such that it no longer binds to its substrate with the same affinity and specificity.
b) As the name suggests, a competitive inhibitor would compete with the substrate for binding at the enzyme. The substrate binds to the active site and so a competitive inhibitor too would bind to the active site of the enzyme.
c) because if the active site is u changed in case of competivie inhibition. It a matter of chance as to whether the substrate would bind or the inhibitor. This chance is greatly dependant on their relative concentration. If the substrate to inhibitor ratio is high the binding of substrate becomes more likely. On the other hand, if a non-competive inhibitor binds and changes the active site, no matter how high the concentration of substrate is it will fail to bind since the shape of the active site is unfit for it.
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