CHEM 1005 COMPREHENSIVE EXAM UPDATED QUESTIONS
AND SOLUTIONS GRADED A+
✔✔a 55 year old man is diagnosed with hyperhomocysteinemia due to a deficiency in
cystathionine-B synthase. In this individual which of the following amino acids could
potentially become essential? - ✔✔cysteine
✔✔hyperpigmentation disorder is primarily due to deficient metabolism of which of the
following amino acids? - ✔✔tyrosine
✔✔serotonin is synthesized from which of the following amino acids? - ✔✔tryptophan
✔✔which of the following is the regulatory enzyme in pyrimidine synthesis? -
✔✔carbamoyl phosphate synthetase II
✔✔methotrexate is a potent anticancer agent that starves dividing cells of
deoxyribonucleotides through direct inhibition of which of the following processes? -
✔✔metabolism of folic acid
✔✔inhibition of folate cycle by 5-fluorouracil will decrease the synthesis of which of the
following metabolites? - ✔✔dTMP
✔✔which of the following enzymes is used directly in the synthesis of dTMP
(thymidine)? - ✔✔thymidylate synthase
✔✔in pyrimidine synthesis, carbamoyl synthetase II can be allosterically activated by
which of the following compounds? - ✔✔5-phosphoribosyl pyrophosphate (PRPP)
✔✔which of the following best describes why purines are recycled? - ✔✔the double ring
structure is difficult to enzymatically break
✔✔which of the following characteristics distinguish most RNA molecules from DNA? -
✔✔uridine based on RNA, whereas a thymidine based on DNA
✔✔in pyrimidine synthesis, uridine triphosphate (UTP) can feedback and inhibit which of
the following enzymes? - ✔✔carbamoyl phosphate synthase II
✔✔inhibition of the folate cycle by 5-fluorouracil will decrease the synthesis of which of
the following metabolites? - ✔✔dTMP
✔✔which of the following compounds contributes to both the sugar and phosphate
groups to the nucleotide bases? - ✔✔PRPP
, ✔✔which of the following enzymes is used directly in the synthesis of dTMP
(thymidine)? - ✔✔thymidylate synthase
✔✔in pyrimidine synthesis, carbamoyl phosphate synthetase II (CPSII) can be
allosterically activated by which of the following compounds? - ✔✔PRPP
✔✔a newborn is suspected of a defect in nucleotide synthesis due to an elevation of
orotic acid. it is determined there is no deficiency in orotate phosphoribosyltransferase.
Based on this presentation, which of the following enzymes is most likely deficient? -
✔✔ornithine transcarbamylase
✔✔which of the following enzymes is the regulatory step in the urea cycle? -
✔✔carbamoyl phosphate synthetase I
✔✔which of the following enzymes is likely to be active in both the fed and active
states? - ✔✔glutaminase
✔✔consider the reaction shown below, which stage of urea biosynthesis does the figure
highlight? - ✔✔transamination
✔✔in the fasted state, when glutamine enters the liver which of the following reactions
occurs? - ✔✔glutamine -> ammonia +glutamate; glutaminase
✔✔which of the following reactions of the urea cycle takes place in the mitochondria? -
✔✔the synthesis of carbamoyl phosphate
✔✔which of the following cofactors or vitamins is required for the conversion of
homocysteine to cysteine? - ✔✔pyridoxal phosphate
✔✔a 52 year old male sought medical attention due to the progressive appearance of
hyperchromic papules on the edge of the second finger of both hands and darkening of
his urine. Tissue biopsy 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? - ✔✔homogentisate oxidase
✔✔glucogenic amino acids can be used in the process of gluconeogenesis and will be
metabolized to all of the following compounds except: - ✔✔acetyl-CoA
✔✔cobalamin supplementation would be the most appropriate in the case of which of
the following enzyme deficiencies? - ✔✔homocysteine methyltransferase
AND SOLUTIONS GRADED A+
✔✔a 55 year old man is diagnosed with hyperhomocysteinemia due to a deficiency in
cystathionine-B synthase. In this individual which of the following amino acids could
potentially become essential? - ✔✔cysteine
✔✔hyperpigmentation disorder is primarily due to deficient metabolism of which of the
following amino acids? - ✔✔tyrosine
✔✔serotonin is synthesized from which of the following amino acids? - ✔✔tryptophan
✔✔which of the following is the regulatory enzyme in pyrimidine synthesis? -
✔✔carbamoyl phosphate synthetase II
✔✔methotrexate is a potent anticancer agent that starves dividing cells of
deoxyribonucleotides through direct inhibition of which of the following processes? -
✔✔metabolism of folic acid
✔✔inhibition of folate cycle by 5-fluorouracil will decrease the synthesis of which of the
following metabolites? - ✔✔dTMP
✔✔which of the following enzymes is used directly in the synthesis of dTMP
(thymidine)? - ✔✔thymidylate synthase
✔✔in pyrimidine synthesis, carbamoyl synthetase II can be allosterically activated by
which of the following compounds? - ✔✔5-phosphoribosyl pyrophosphate (PRPP)
✔✔which of the following best describes why purines are recycled? - ✔✔the double ring
structure is difficult to enzymatically break
✔✔which of the following characteristics distinguish most RNA molecules from DNA? -
✔✔uridine based on RNA, whereas a thymidine based on DNA
✔✔in pyrimidine synthesis, uridine triphosphate (UTP) can feedback and inhibit which of
the following enzymes? - ✔✔carbamoyl phosphate synthase II
✔✔inhibition of the folate cycle by 5-fluorouracil will decrease the synthesis of which of
the following metabolites? - ✔✔dTMP
✔✔which of the following compounds contributes to both the sugar and phosphate
groups to the nucleotide bases? - ✔✔PRPP
, ✔✔which of the following enzymes is used directly in the synthesis of dTMP
(thymidine)? - ✔✔thymidylate synthase
✔✔in pyrimidine synthesis, carbamoyl phosphate synthetase II (CPSII) can be
allosterically activated by which of the following compounds? - ✔✔PRPP
✔✔a newborn is suspected of a defect in nucleotide synthesis due to an elevation of
orotic acid. it is determined there is no deficiency in orotate phosphoribosyltransferase.
Based on this presentation, which of the following enzymes is most likely deficient? -
✔✔ornithine transcarbamylase
✔✔which of the following enzymes is the regulatory step in the urea cycle? -
✔✔carbamoyl phosphate synthetase I
✔✔which of the following enzymes is likely to be active in both the fed and active
states? - ✔✔glutaminase
✔✔consider the reaction shown below, which stage of urea biosynthesis does the figure
highlight? - ✔✔transamination
✔✔in the fasted state, when glutamine enters the liver which of the following reactions
occurs? - ✔✔glutamine -> ammonia +glutamate; glutaminase
✔✔which of the following reactions of the urea cycle takes place in the mitochondria? -
✔✔the synthesis of carbamoyl phosphate
✔✔which of the following cofactors or vitamins is required for the conversion of
homocysteine to cysteine? - ✔✔pyridoxal phosphate
✔✔a 52 year old male sought medical attention due to the progressive appearance of
hyperchromic papules on the edge of the second finger of both hands and darkening of
his urine. Tissue biopsy 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? - ✔✔homogentisate oxidase
✔✔glucogenic amino acids can be used in the process of gluconeogenesis and will be
metabolized to all of the following compounds except: - ✔✔acetyl-CoA
✔✔cobalamin supplementation would be the most appropriate in the case of which of
the following enzyme deficiencies? - ✔✔homocysteine methyltransferase
