BIOC Practice Questions

Transamination of pyruvate with glutamate as amino donor gives: A. Alanine B. Serine C. Cysteine D. Aspartate E. Valine

Alanine

Glutamine synthetase is activated by which of the following molecules? a. glycine b. AMP c. CTP d. carbamoyl phosphate e. none of the above

E. none of the above -glutamine synthetase is activated by ATP

Ornithine is not considered an amino acid since it is not incorporated into proteins.

False.

Amino acids biosynthesized from aspartate include all of the following EXCEPT: A. Asparagine B. Threonine C. Methionine D. Lysine E. Glutamate

Glutamate

The carbon skeletons of all of the amino acids below converge to pyruvate EXCEPT: a. alanine. b. serine. c. cysteine. d. glycine. e. glutamate.

Glutamate

What are the two enzymes that represent the two most significant enzymes in the removal of ammonia from cells within the body?

Glutamate dehydrogenase and glutamine synthetase

Serotonin is made from what amino acid?

Tryptophan

All are convergent metabolic intermediates of αamino acid carbon skeletons EXCEPT: a. Citrate. b. αketoglutarate. c. Oxaloacetate. d. succinylCoA. e. Fumarate.

A. Citrate

Elevated levels of homocysteine in the blood is related to all EXCEPT: A. Homocysteinuria at very high levels B. Folic acid deficiency C. Folic acid-dependent conversion of homocysteine to methionine D. Higher risk of heart attack and stroke E. All of the above are correct

E. All are correct

How many equivalents of ATP are consumed in the production of one equivalent of urea by the urea cycle?

1 ATP -explain *remember: NADH = 2.5 ATP

Glutamine synthetase is an important enzyme in the regulation of ammonia concentrations. Which of the following would be an activator of Gln synthetase? a. αketoglutarate b. glutamine c. histidine d. alanine e. none of the above

A. Alpha-ketoglutarate

Glutamate synthase catalyzes the reaction ____ + ____ + ____ → 2 glutamate + NADP+ a. αketoglutarate; NADPH; glutamine b. glutamate; αketoglutarate; NADH c. glutamylphosphate; glutamine; NADPH d. Nacetylglutamate; αketoglutarate; NADH e. none are true

A. Alpha-ketoglutarate; NADPH; glutamine

What reaction does glutamate dehydrogenase (GDH) catalyze? a. The reductive amination of αketoglutarate to yield glutamate. b. Phosphorylation of carbamate to yield carbamoylphosphate. c. The amidation of the γcarboxyl group of glutamate to form glutamine. d. The deadenylation of glutamine synthetase. e. The adenylation of glutamine synthetase.

A. Glutamate dehydrogenase (GDH) catalyzes the reaction of the reductive amination of alpha-ketoglutarate to yield glutamate. (dehydrogenase reactions require B1, B2, B3, B5, and lipoic acid)

Which of the following is NOT a commonly used transamination pair? a. Phe / phenylpyruvate b. Asp / oxaloacetate c. Glu / αketoglutarate d. Ala / pyruvate e. all are correct

A. Phe/Phenylpyruvate

In the process of amino acid biosynthesis, how are glutamic acid, glutamine, proline, and arginine all related? a. They are all derived from αKG. b. They are all derivatives of acetyl CoA. c. They are all derivatives of pyruvate. d. They are all derived from aspartate. e. They are all derivatives of 3phosphoglycerate.

A. They are all derived from alpah-ketoglutarate

A deficiency of which one of the following proteolytic enzymes would have the greatest effect on digestion of proteins? A. Trypsin B. Chymotrypsin C. Carboxypeptidase A D. Pepsin E. Aminopeptidase

A. Trypsin

All of the following are characteristics of phenylketonuria EXCEPT: a. excretion of phenylpyruvate. b. air oxidation causes urine to turn dark on standing. c. treated by putting patient on a diet low in phenylalanine. d. untreated patients suffer severe mental retardation. e. deficiency or defect in phenylalanine hydroxylase.

B. Air oxidation causes urine to turn dark on standing

Ornithine serves three metabolically important roles, but is not found in proteins. What is one of the important roles of ornithine? a. amine donor for many transamination reactions b. an intermediate in the urea cycle c. involved in the synthesis of serine, which serves as a precursor for glycine and cysteine d. its reaction with methenyl tetrahydrofolate produces lysine e. none of the above

B. An intermediate in the urea cycle

A high homecysteine level could be associated with a deficiency of which of the following vitamins? A. B3 B. B12 C. C D. E E. B1

B. B12

The term ketogenic amino acids refers to amino acids: a. that are precursors for glucose synthesis. b. degraded to yield acetyl CoA or acetoacetate. c. that can not be converted to fatty acids or ketone bodies. d. degraded to yield succinylCoA, pyruvate, αketoglutarate, fumarate and oxaloacetate. e. none of the above.

B. Degraded to yield acetyl CoA or acetoacetate

Degradation of valine, isoleucine and methionine leads to succinylCoA via the sequence of: A. carboxylation using biotin and ATP B. mutase C. methylmalonylCoA D. epimerase E. PropionylCoA a. E, B, A, C, D, C b. E, A, C, D, C, B c. A, C, D, C, E, B d. C, A, D, B, C, E e. D, A, C, B, C, E

B. E, A, C, D, C, B -propionyl-CoA -carboxylation using Biotin and ATP -methylmalonyl-CoA -epimerase -methylmalonyl-CoA -mutase -Succinyl CoA

The reaction, 2 NH4+ + αketoglutarate + NADPH + ATP → glutamine + NADP+ + ADP + Pi + H2O, is the combined result of what two enzymes? a. first, glutamate synthase, then glutamate dehydrogenase b. first, glutamate dehydrogenase ,then glutamine synthetase c. first, glutamine synthetase, then glutamate synthase d. first, glutamine synthetase, then glutamate dehydrogenase e. none of the above

B. First: Glutamate dehydrogenase then glutamine synthetase

Which of the following amino acids plays the most central role in nitrogen and amino acid metabolism? a. Asn b. Glu c. Gly d. Cys e. none of the above

B. Glu

A reduction in the metabolism of which one of the following amino acids can lead to elevated homocysteine levels in the blood? A. Alanine B. Methionine C. Phenylalanine D. Glutamate E. Cysteine

B. Methionine

Which of the following is NOT a commonly used transamination pair? A. Alpha-ketoglutarate --> glutamate B. Serine --> 3-PG C. Alanine --> pyruvate D. Aspartate --> OAA

B. Serine --> 3-PG

Which of the following directly serves as one of the nitrogen atoms of a urea molecule? a. the amide N of Asn b. the N of Asp c. the Rgroup N of Lys d. the N of glucosamine e. none of the above

B. The N of Asp

The carbon excreted with urea within urine is originally derived from?

Bicarbonate

A 5-day old infant intially began feeding poorly, grew irritable, then very lethargic. The diaper, when changed, had a musky, sweet odor to it. At the emergency department at the local hospital, the child was suspected of having an inborn error of metabolism, and blood work was ordered. You would expect to see an elevation in what possilbe amino acids?

Branch chain amino acids 1. Isoleucine 2. Leucine 3. Valine

An infant who appeared normal at birth began to develop lethargy, hypothermia, and apnea within 24 hrs. An anaylysis of blood components indicated high levels of ammonia and citrulline, and low levels of urea. The most likely defective enzyme in this child is which of the following? A. Carbamoyl phosphate synthetase I B. Ornithine transcarbamoylase C. Argininosuccinate synthetase D. Argininosuccinate lyase E. Arginase

C. Arginosuccinate synthetase

The reaction, glutamate + NAD(P)+ + H2O → NH4+ + αketoglutarate + NAD(P)H + H+, is catalyzed by: a. Nitrogenase. b. carbamoylphosphate synthetase (CPSI). c. glutamate dehydrogenase (GDH). d. glutamine synthetase (GS). e. none are true.

C. Glutamate dehydrogenase is reversible and can catalyze the reaction of glutamate to alpha-ketoglutarate.

Nacetylglutamate functions in ammonium incorporation into metabolic intermediates as: a. a coenzyme for glutamine synthetase (GS). b. a competitive inhibitor for glutamine synthetase (GS). c. an allosteric activator for carbamoylphosphate synthetase I (CPSI). d. the energy source needed for the reductive amination of αketoglutarate (αKG) to yield glutamate. e. the substrate for the amination of the γglutamylphosphate.

C. N-acetyleglutamate functions as an allosteric activator for carbamoyl-phosphate synthetase (CPS-1)

___ is an intermediate in biosynthesis of ornithine and a regulator of carbamoylphosphate synthetaseI a. γGlutamylphosphate b. αKetoglutarate c. NAcetylglutamate d. Glutamine e. Glutamine5phosphate

C. N-acetylglutamate

All of the following are characteristics of alkaptonuria EXCEPT: a. excretion of homogentisate b. air oxidation causes urine to turn dark on standing c. results in mental retardation due to accumulation of Phe metabolites d. homogentisate accumulation in joints may cause arthritis e. all are true

C. Results in mental retardation due to accumulation of Phe metabolits

All of the following are true of transamination EXCEPT: a. It is characterized by the transfer of an αamino group from an amino acid to the αketo position of an αketo acid. b. The amino donor becomes an αketo acid. c. The coenzyme needed is thiamin pyrophosphate (TPP). d. Humans are capable of synthesizing the αketo acid analog of nonessential amino acids and using transamination to form the amino acids, but are not able to construct carbon skeletons of the essential amino acids. e. The αketo acid acceptor becomes an αamino acid.

C. The coenzyme needed is thiamin pyrophosphate (TPP)

All of the carbons and nitrogens of ornithine come biosynthetically from: a. proline. b. valine. c. alanine. d. glutamate. e. glycine.

D. Glutamate

Which of the following is both an essential amino acid (for humans) and also an exclusively ketogenic amino acid? a. proline b. valine c. glutamine d. leucine e. phenylalanine

D. Leucine -lysine is also purely ketogenic

Which one of the following occurs in the urea cycle? A. Carbamoyl phosphate is derivd directly from glutamine and CO2 B. Ornithine reacts with aspartate to generate argininosuccinate. C. The alpha-amino group of arginine forms one of the nitrogens of urea D. Ornithine directly reacts with carbamoyl phosphate to form citruline E. N-acetylglutamate is a positive allosteric regulator of ornithine transcarbamoylase.

D. Ornithine directly reacts with carbamoyl phosphate to form citruline

All of the following are true of the urea cycle EXCEPT: a. It helps in the excretion of excess nitrogen. b. It is mainly confined to the liver. c. It is linked to the citric acid cycle through fumarate. d. Stimulation of carbamoylphosphate synthetase I (CPSI) decreases the activity of the urea cycle. e. It is completed by the regeneration of ornithine from arginine.

D. Stimulation of Carbamoyl-phosphate synthetase (CPS-1) decreases the activity of the urea cycle

All are characteristics of Maple Syrup Urine Disease EXCEPT: a. hereditary enzyme defect. b. elevated levels of val, leu, and ile and their corresponding αketo acids in blood and urine. c. restrictive intake of proteins with val, leu and ile is required. d. fatal without detection and treatment. e. elevated blood levels of acetoacetate and βhydroxybutyrate.

E. Elevated levels of acetoacetate and B-hydroxybutyrate

What reaction catalyzes the reaction of forming glutamate from glutamine?

Glutaminase

A 34-year old female has a history of intermittent episodes of severe abdominal pain. She has had multiple abdominal surgeries and exploratory procedures with no abnormal findings. Her urine appears dark during an attack and gets even darker if exposed to sunlight. The attacks seem to peak after she takes erythromycin, due to her penicillin allergy. This patient most likely has difficulty in synthesizing which of the following? A. Heme B. Creatine phosphate C. Cysteine D. Thymine E. Methionine

Heme

Urea synthesis occurs partly in the mitochondria and partly in the cytosol of the _________

Hepatocytes

What does CPS-1 do to the urea cycle?

Increases the activity of the urea cycle

Which three amino acids can not readily undergo transamination to an appreciable extent, thereby making them ineffective in lowering blood nitrogen concentrations in patients with kidney disease?

Lysine, Threonine, Histidine

Aspartate is formed from the transamination of: A. Asparagine B. Aspartame C. Oxaloacetate D. Citrate E. Alpha-ketoglutarate

Oxaloacetate

What is the correct order of enzyme activities in the acquisition of amino acids from dietary sources?

Pepsin --> trypsin --> carboxypeptidases --> dipeptidases

What vitamin is essential in amino acid metabolism?

Pyridoxal phosphate (B6) -used as a coenzyme in aminotransferase reactions

In liver disease, the enzymes AST and ALT leak into the blood from damaged liver cells. Both of these enzymes have what in common?

They both convert alpha-keotglutarate to glutamate

A 3 year old from Russia, after immigrating to the US, was found to have developmental delays and severe mental retardation. Elevated levels of phenylalanine and phenylpyruvate were found in the blood. The child was placed on a low-PHE diet, but there was no improvement in the child. Given this information, the child would be expected to have difficulty undergoing what conversion?

Tyrosine to dopamine

What coenzyme is needed for transamination reactions?

Vitamin B6 (PLP)