Unit 4

Question 1

Which of the following enzymes is likely to be active in both the fed and fasted states?

Answer 1

Glutaminase

Question 2

The reaction of ammonia with α-ketoglutarate is catalyzed by _________ and requires _________ as a reactant.

Answer 2

Glutamate dehydrogenase; NADH or NADPH

Question 3

Which of the following enzymes is correctly paired with its activator?

Answer 3

N-acetylglutamate synthtase; arginine

Question 4

The transamination of all amino acids requires which of the following cofactors?

Answer 4

Pyridoxal phosphate (PLP)

Question 5

The glucose-alanine cycle is a method of transferring ammonia from the skeletal muscle to the liver. In this process the non-toxic carrier of ammonia is which of the following compounds?

Answer 5

Alanine

Question 6

Which of the following urea cycle enzymes catalyzes the reaction hydrolyzing the release of urea from arginine?

Answer 6

Arginase

Question 7

Which of the following enzymes is regulated by N-acetylglutamate (NAGs)?

Answer 7

Carbamoyl phosphate synthetase I (CPS I)

Question 8

The urea cycle takes place in which of the following subcellular locations?

Answer 8

The cytosol and the mitochondria

Question 9

A 52 y/o man sought medical help complaining about progressive appearance of hyperchromic (hyperpigmented) papules on the edge on the second finger of both hands. He also complained about darkening of urine. Incisional biopsy of one of the spots on his hands and urine sample tested positive for or 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?

Answer 9

Homogentisate oxidase

Question 10

Hyperhomocysteinemia

Answer 10

genetic causes - enzymatic deficiencies, cystathionine-B synthase, methyltransferase

metabolic causes- cofactor deficiencies, cobalamin, folate

Question 11

MSUD

Answer 11

Deficient oxidative carbolxylation of the metabolites isoleucine, leucine, and valine

Question 12

A 15-year-old female presents to her pediatrician with concerns over her inability to sleep, increased feelings of depression and generalized fatigue. A full laboratory work-up is ordered and based on these findings she is diagnosed with a melatonin deficiency. Based on this information, metabolism of which of the following amino acids is likely impaired?

Answer 12

Tryptophan

Question 13

Phenylketonuria can be caused by an enzymatic deficiency or it can present due to a deficiency in which of the following required metabolic cofactors?

Answer 13

Tetrahydrobiopterin (BH4)

Question 14

A 17-year old female presents to her primary care and is diagnosed with a Vitamin B12 (cobalamin) deficiency. In this individual, which of the following reactions would be compromised?

Answer 14

Conversion of methyl malonyl-Co A to succinyl-CoA

Question 15

You and a friend are being chased by a bear. Under these conditions levels of epinephrine are increased due to metabolism of which of the following amino acids?

Answer 15

Tyrosine

Question 16

Which of the following compounds or substrates is required for the synthesis of tyrosine? (+ indicates the compound is required; - indicates the compound is not required)

Answer 16

4

Question 17

Homocystinuria can be caused by several different enzyme or vitamin deficiencies. An elevation of homocysteine and a decrease in cysteine would most likely present due to which of the following deficiencies?

Answer 17

Loss of function of cystathionine-β synthase

Question 18

A deficiency in B6 (pyridoxal phosphate) would negatively impact which of the following pathways:

Answer 18

1 only

Question 19

An elevation of purine nucleotides will negatively regulate pyrimidine synthesis through which of the following mechanisms?

Answer 19

Inhibiting the activity of carbamoyl phosphate synthetase II

Question 20

Methotrexate is a potent anticancer agent that starves dividing cells of deoxyribonucleotides through direct inhibition of which of the following processes?

Answer 20

Metabolism of folic acid

Question 21

The conversion of ribose bases into deoxy-bases will be occurring under which of the following conditions?

Answer 21

When cells are proliferating

Question 22

Which of the following enzymes is used directly in the synthesis of dTMP (thymidine)?

Answer 22

Thymidylate synthase

Question 23

A 4-year-old girl presented to the clinic with megaloblastic anemia and failure to thrive. Urinalysis showed significant sediment with extremely high levels of orotic acid. A deficiency in which of the following enzymes would be consistent with this presentation?

Answer 23

Orotate phosphoribosyltransferase

Question 24

Which of the following is the common intermediate for purine synthesis?

Answer 24

Inosine monophosphate

Question 25

A 40-year-old male comes in to the doctor’s office with severe pain in his big toe. He is diagnosed with gout. Allopurinol is administered and this drug will inhibit which of the following enzymes?

Answer 25

Xanthine oxidase

Question 26

Folate is an essential compound in the synthesis of nucleotides. All of the following nucleotides require folate for synthesis except:

Answer 26

CTP

Question 27

Which of the following characteristics distinguish most RNA molecules from DNA?

Answer 27

Uridine base on RNA, whereas a thymidine base on DNA

Question 28

In pyrimidine synthesis, carbamoyl phosphate synthetase II (CPSII) can be allosterically activated by which of the following compounds?

Answer 28

5-phosphoribosyl 1-pyrophosphate (PRPP)

Question 29

Which of the following reactions of the urea cycle takes place in the mitochondria?

Answer 29

The synthesis of carbamoyl phosphate

Question 30

A newborn infant was resuscitated at birth and was found to be neurologically compromised, with marked flaccidity (lack of muscle tone), and cardiac insufficiency. Glutamine was largely absent from the serum and ammonia levels were excessively elevated and urea production was otherwise not impaired. Based on this information which of the following enzymes is likely deficient in this infant?

Answer 30

Glutamine synthetase

Question 31

A comatose infant is brought to the ER. In the course of the examination, plasma ammonia was found to be elevated 20-fold over normal values. Urine orotic acid and uracil were both greater than normal. A defect of which of the following enzymes is the most likely diagnosis?

Answer 31

Ornithine transcarbamoylase

Question 32

Which of the following non-essential amino acids is synthesized as part of the urea cycle?

Answer 32

Arginine

Question 33

Ubiquitination is a means of targeting a protein for which of the following cellular processes?

Answer 33

Proteasomal degradation

Question 34

A patient recently diagnosed with colon cancer is being treated with 5-fluorouracil. Which of the following enzymes will this drug directly inhibit?

Answer 34

Thymidylate synthase

Question 35

In pyrimidine synthesis, uridine triphosphate (UTP) can feedback and inhibit which of the following enzymes?

Answer 35

Carbamoyl phosphate synthase II

Question 36

In the salvage of purines, hypoxanthine-guanine phosphoribosyl transferase (HGPRT) is responsible for which of the following processes?

Answer 36

Conversion of guanine to guanosine monophosphate (GMP)

Question 37

The regulation of PRPP synthetase is critical in the production of both purines and pyrimidines. This enzyme is inhibited under which of the following conditions?

Answer 37

When both GDP and ADP are elevated

Question 38

Glucogenic amino acids that are used used in the process of gluconeogenesis and will be metabolized to all of the following compounds except:

Answer 38

Acetyl-CoA

Question 39

An individual is suspected of having a deficiency in branched chain keto acid dehydrogenase. Supplementation of which of the following vitamins or cofactors may help resolve this issue?

Answer 39

Thiamine

Question 40

A 55-year old man presents to his primary care physician with bouts of dizziness and confusion. He is diagnosed with hyperhomocysteinemia due to a deficiency of cystathionine-ß synthase. In this individual which of the following amino acids could potentially become essential?

Answer 40

Cysteine

Question 41

An infant is normal at birth but becomes lethargic after several feedings. The assigned nurse describes an unusual smell to the urine but is ignored. Infection (sepsis) is suspected, and blood tests show normal white blood cell counts with a serum pH of 7.0. Evaluation for an inborn error of metabolism shows an abnormal amino acid screen. The report states that branch-chain amino acids are strikingly elevated. Elevation of which of the following amino acids would be consistent with the report?

Answer 41

Isoleucine

Question 42

Which of the following amino acids is essential?

Answer 42

Methionine

Question 43

S-adenosylmethionine (SAM) is synthesized from ATP and methionine. A deficiency in which of the following enzymes would impair the production of SAM?

Answer 43

Methionine adenosyltransferase (MAT)