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This is in regards to the Khan Academy bio passage "The genetic basis of phenylketonuria". I'm a little confused by the method here because I haven't really taken a biochem class. I'm gonna basically post every question, and the answer, then state why i'm confused. Please note that i'm not gonna list the passage here, so i'm assuming you already know what phenylketonuria is:
1. How would you expect the mutation associated with PKU to affect the catalytic efficiency of phenylalanine transaminase? Answer: Neither Kcat nor Km will change, leading to an unchanged catalytic efficiency.
I'm assuming that since this is a deactivating mutation, the kcat and Km are inherent properties of the enzyme, so these will be unchanged?
3. How would you expect the mutation associated with PKU to affect the rate of the reaction catalyzed by phenylalanine transaminase? Answer: The reaction rate will increase, due to an increase in the concentration of phenylalanine.
Ok so for this one, I understand that they're basically using the Michaelis-Mentin equation straight plug n chug style. So more on top means higher rate? I don't really get why this would happen though because wouldn't a defective enzyme mean that there is less turnover happening? Or since [E] isn't in the equation then that wouldn't matter.
4. Individuals heterozygous for the PKU mutation have very slightly increased levels of phenylalanine. How would you expect the phenylalanine hydroxylase reaction rate of an individual heterozygous for the PKU mutation to be different in than an individual with no mutated genes? Answer: The reaction rate would decrease due to a decrease in the reaction’s Vmax
I'm thrown off here now. I thought extra substrate means faster rate, according to the previous questions? I get that the heterozygous individual has a defective, and not inactive enzyme, but why would it be different in this case?
5. Which of the following would best represent the outcome of an individual with the PKU mutation consuming a meal with a high phenylalanine content? Answer: The phenylalanine transaminase catalyzed reaction rate would increase, and the concentration of phenylalanine would increase significantly.
Now we're back to the reaction increasing from excess substrate, with a defective enzyme. I'm thrown off because in the last question it was decreased rate.
I know this is long, so if anyone is willing to help, I will highly appreciate it. It would really be helpful.
1. How would you expect the mutation associated with PKU to affect the catalytic efficiency of phenylalanine transaminase? Answer: Neither Kcat nor Km will change, leading to an unchanged catalytic efficiency.
I'm assuming that since this is a deactivating mutation, the kcat and Km are inherent properties of the enzyme, so these will be unchanged?
3. How would you expect the mutation associated with PKU to affect the rate of the reaction catalyzed by phenylalanine transaminase? Answer: The reaction rate will increase, due to an increase in the concentration of phenylalanine.
Ok so for this one, I understand that they're basically using the Michaelis-Mentin equation straight plug n chug style. So more
4. Individuals heterozygous for the PKU mutation have very slightly increased levels of phenylalanine. How would you expect the phenylalanine hydroxylase reaction rate of an individual heterozygous for the PKU mutation to be different in than an individual with no mutated genes? Answer: The reaction rate would decrease due to a decrease in the reaction’s Vmax
I'm thrown off here now. I thought extra substrate means faster rate, according to the previous questions? I get that the heterozygous individual has a defective, and not inactive enzyme, but why would it be different in this case?
5. Which of the following would best represent the outcome of an individual with the PKU mutation consuming a meal with a high phenylalanine content? Answer: The phenylalanine transaminase catalyzed reaction rate would increase, and the concentration of phenylalanine would increase significantly.
Now we're back to the reaction increasing from excess substrate, with a defective enzyme. I'm thrown off because in the last question it was decreased rate.
I know this is long, so if anyone is willing to help, I will highly appreciate it. It would really be helpful.