Unit 4 Exam

A deficiency in vitamin B6 (pyridoxal phosphate) would negatively impact which of the following pathways:
1. Metabolism of cysteine to homocysteine
2. Metabolism of phenylalanine to tyrosine
3. Conversion of methyl malonyl-Co A to succinyl-CoA
- 1 only
- 2 only
- 2 and 3
- 1 and 2
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A deficiency in vitamin B6 (pyridoxal phosphate) would negatively impact which of the following pathways:
1. Metabolism of cysteine to homocysteine
2. Metabolism of phenylalanine to tyrosine
3. Conversion of methyl malonyl-Co A to succinyl-CoA
- 1 only
- 2 only
- 2 and 3
- 1 and 2
- 1 only

Outline the metabolic pathways for tyrosine, phenylalanine, methionine, cysteine and branched-chain amino acids, and identify reactions associated with clinically significant metabolic disorders.
Which of the following cofactors or vitamins is required for the conversion of homocysteine to cysteine?
- Tetrahydrobiopterin (BH4)
- Cobalamin
- Folate
- Pyridoxal phosphate (PLP)
- Pyridoxal phosphate (PLP)

Outline the metabolic pathways for tyrosine, phenylalanine, methionine, cysteine and branched-chain amino acids, and identify reactions associated with clinically significant metabolic disorders.
An elevation of homocysteine and a decrease in cysteine would most likely be present due to which of the following deficiencies?
- Loss of function of methionine synthase
- Cobalamin deficiency
- Loss of function of cystathionine-β synthase
- Tetrahydrobiopterin (BH4) deficiency
- Loss of function of cystathionine-β synthase

Outline the metabolic pathways for tyrosine, phenylalanine, methionine, cysteine and branched-chain amino acids, and identify reactions associated with clinically significant metabolic disorders.
Supplementation of which of the following cofactors/coenzymes may assist the activity of branched-chain ketoacid dehydrogenase?
- Pyridoxal phosphate (PLP)
- Cobalamin
- Thiamine
- Tetrahydrobiopterin (BH4)
- Folate
- Thiamine

Identify the specific metabolic defects in hypervalinemia, maple syrup urine disease, intermittent branched-chain ketonuria, isovaleric acidemia, and methylmalonic aciduria
In the salvage of purines, hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is responsible for which of the following processes?
- Conversion of guanine to guanosine monophosphate (GMP)
- Conversion of inosine monophosphate to inosine
- Conversion of adenine to adenosine monophosphate (AMP)
- Conversion of hypoxanthine to xanthine
- Conversion of guanine to guanosine monophosphate (GMP)

Write the structure of the end product of purine catabolism. Comment on its solubility and indicate its role in gout, Lesch-Nyhan syndrome, and von Gierke disease.
In pyrimidine synthesis, carbamoyl phosphate synthetase II (CPSII) can be allosterically activated by which of the following compounds?
- 5-phosphoribosyl pyrophosphate (PRPP)
- Carbamoyl phosphate
- Uridine triphosphate (UTP)
- Adenosine triphosphate (ATP)
- 5-phosphoribosyl pyrophosphate (PRPP)

Compare and contrast the roles of dietary nucleic acids and of de novo biosynthesis in the production of purines and pyrimidines destined for polynucleotide biosynthesis, including the reaction by phosphoribosyl 1-pyrophosphate synthetase. Carbamoyl phosphate synthetase II (CPSII) is the primary regulatory enzyme, activated by PRPP and inhibited by purine bases.
Methotrexate (image below) is classified as an "antimetabolite." Methotrexate most closely resembles which endogenous compound?
- Folate
- Epinephrine
- Aspartic acid
- 5-hydroxytryptamine
- Histamine
- Folate

Explain why antifolate drugs and analogs of the amino acid glutamine inhibit purine biosynthesis.
An elevation of purine nucleotides will negatively regulate pyrimidine synthesis through which of the following mechanisms?
- Increasing the activity of the non-oxidative reactions of the pentose pathway
- Increasing degradation of pyrimidine bases
- Inhibiting the activity of carbamoyl phosphate synthetase II (CPSII)
- Inhibiting the activity of thymidylate synthase
- Inhibiting the activity of carbamoyl phosphate synthetase II (CPSII)

Elevated purines will directly reduce the activity of carbamoyl phosphate synthetase II
Which of the following is the common intermediate for purine synthesis?
- Inosine monophosphate (IMP)
- Cytidine monophosphate (CMP)
- Hypoxanthine
- Orotate monophosphate (OMP)
- Inosine monophosphate (IMP)

Outline the sequence of reactions that convert inosine monophosphate (IMP), first to AMP and GMP, and subsequently to their corresponding nucleoside triphosphates.
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?
- Pyruvate
- Glutamine
- Urea
- Alanine
- Alanine

Illustrate the central roles of transaminases (aminotransferases), of glutamate dehydrogenase, glutamine synthetase, and of glutaminase in human nitrogen metabolism.
Which of the following enzymes is likely to be active in both the fed and fasted states? - Hormone-sensitive lipase - Glycogen synthase - Pyruvate kinase - Glutaminase- Glutaminase Illustrate the central roles of transaminases (aminotransferases), of glutamate dehydrogenase, glutamine synthetase, and of glutaminase in human nitrogen metabolism.Which of the following reactions of the urea cycle takes place in the mitochondria? - The synthesis of carbamoyl phosphate - The synthesis of argininosuccinate - The synthesis of urea - The synthesis of arginine- The synthesis of carbamoyl phosphate Describe the reactions that convert NH3, CO2, and the amide nitrogen of aspartate into urea, and identify the subcellular locations of the enzymes that catalyze urea biosynthesis.Which of the following statements is consistent with protein catabolism in the fed state? - High levels of arginine will stimulate the activity of urea synthesis - The conversion of alpha-ketoglutarate to glutamate will be favored in the liver - Amino acids will be used as a substrate for gluconeogenesis - Glutaminase activity in the liver will be low- High levels of arginine will stimulate the activity of urea synthesis Describe the reactions that convert NH3, CO2, and the amide nitrogen of aspartate into urea, and identify the subcellular locations of the enzymes that catalyze urea biosynthesis.The reaction of ammonia with α-ketoglutarate is catalyzed by _________ and requires _________ as a reactant. - glutamate synthetase; ATP - glutamate dehydrogenase; ATP - glutamate synthetase; NADH or NADPH - glutamate dehydrogenase; NADH or NADPH- glutamate dehydrogenase; NADH or NADPH Illustrate the central roles of transaminases (aminotransferases), of glutamate dehydrogenase, glutamine synthetase, and of glutaminase in human nitrogen metabolism.