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Unit 4 test UNE medical biochemistry Questions and Answers
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Unit 4 test UNE medical biochemistry Questions and Answers
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Unit 4 test UNE medical biochemistryQuestions and answers
A deficiency in which of the following enzymes will NOT result in an increase in orotic
acid?
a. N-acetylglutamate synthetase
b. Ornithine transcarbamoylase
c. Argininosuccinate synthetase
d. Argininosuccinate lyase - Answers -N-acetylglutamate synthetase (NAG synthetase
Feedback: deficiencies in NAG synthetase or carbamoyl phosphate synthetase I will
NOT result in an increase in orotic acid.
Which of the following enzymes is correctly paired with its activator?
a. N-acetylglutamate synthtase; arginine
b. Carbamoyl phosphate synthetase I; ATP
c. Glutaminase; citrate
d. Arginase; NADH - Answers -N-acetylglutamate synthtase; arginine
Feedback: arginine (an intermediate of the urea cycle), stimulates the synthesis of NAG
by allosterically activating the enzyme N-acetylglutamate synthase
Which of the following enzymes is regulated by N-acetylglutamate (NAGs)?
a. Carbamoyl phosphate synthetase II
b. Ornithine transcarbamoylase
c. Carbamoyl phosphate synthetase I
d. Arginosuccinate lyase - Answers -Carbamoyl phosphate synthetase I (CPS I)
Feedback: CPS I is the regulatory enzyme of the urea cycle and is stimulated by NAG
Your patient presents with a deficiency of the enzyme that catalyzes synthesis of N-
acetylglutamate (NAGs). Which of the following will be a consequence of this deficiency
in the patient?
a. increased fatty acids in the blood
b. increased amino acids in the blood
c. decreased excretion of uric acid
d. increased glucose in the blood - Answers -Increased amino acids in the blood
NAG is an essential activator of CPS I which catalyzes the first step in the urea cycle.
Loss of this activator will decrease urea cycle activity, which will increase the amount of
amino acids in the blood.
, The urea cycle takes place in which of the following subcellular locations?
a. the cytosol and the mitochondria
b. the cytosol only
c. the nucleus and the mitochondria
d. the mitochondria only - Answers -the cytosol and the mitochondria
Which of the following non-essential amino acids is synthesized as part of the urea
cycle?
a. Asparagine
b. Aspartate
c. Lysine
d. Arginine
e. Glutamine - Answers -arginine
Several amino acids are intermediates of the urea cycle, having side ammonia groups
that join with free Co2 and ammonia to produce net excretion of ammonia as urea.
Which of the following amino acids has a nitrogen in its side chain AND is an
intermediate of the urea cycle?
a. asparagine
b. glutamate
c. phenylalanine
d. arginine - Answers -arginine
Which of the following reactions of the urea cycle takes place in the mitochondria?
a. the synthesis of urea
b. the synthesis of argininosuccinate
c. the synthesis of carbamoyl phosphate
d. the synthesis of arginine - Answers -the synthesis of carbamoyl phosphate
A 52-year-old male sought medical help complaining about a progressive appearance of
hyperchromic papules on the edge of the second finger. Incisional biopsy of one of the
spots on his hands and urine sample tested positive for homogentisic acid. Based on
these findings a diagnosis of alkaptonuria is made. This diagnosis is consistent with a
deficiency in which of the following enzymes?
a. phenylalanine hydroxylase
b. tyrosinase
c. homogentisate oxidase
d. α-ketoacid dehydrogenase - Answers -homogentisate oxidase
Which of the following best describes the process of transamination?
a. the transfer of an amino group from an amino acid to a keto-acid
b. the release of free ammonia from an amino acid
c. the transfer of a carboxyl group to a keto acid - Answers -the transfer of an amino
group from an amino acid to a keto acid
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