Quiz 17 Nitrogen Metabolism

What compound is oxidatively deaminated to yield an ammonium ion?

glutamate

What amino acids are solely ketogenic?

leucine and lysine

Thymidylate is formed from:

dUMP

In the urea cycle, the carbon skeleton of aspartate is preserved as:

fumarate.

N-Acetylglutamate synthase is activated by:

arginine.

What enzyme is the target for competitive inhibition by methotrexate?

dihydrofolate reductase

Which product is regenerated in oxidative deamination of glutamate?

α-ketoglutarate

What form is an ammonium ion converted into in most terrestrial vertebrates?

urea

Excessive alcohol consumption not only makes you overweight, it can also lead to ammonia poisoning. How is alcohol metabolism linked to increased levels of blood ammonia?

Excessive alcohol consumption can cause liver damage, the primary site of urea formation. A loss of liver function can lead to increased ammonia in the blood.

What enzyme initiates degradation of threonine?

threonine deaminase

What amino acid is formed in a reaction catalyzed by ornithine transcarbamylase?

citrulline

What is the third stage of liver damage from excessive ethanol consumption?

cirrhosis

What can be used as a reducing power by glutamate dehydrogenase?

either NADH or NADPH

Where does the urea cycle begin?

mitochondria

What complex is formed on the enzyme when a product is replaced by a substrate before the reaction is complete?

abortive complex

How many molecules of ATP does the synthesis of carbamoyl phosphate require?

2

What molecule is the direct product of adenylation of methionine?

S-adenosyl methionine

What allosteric regulator is required for carbamoyl phosphate synthetase activity?

N-acetylglutamate

What enzymes catalyze the transfer of an a-amino group from an α-amino acid to an α-ketoacid?

aminotransferases

How much urea is excreted by a human being per year?

10 kg

In what principal transport forms is nitrogen transported from muscle to the liver?

alanine and glutamine

What molecule can aspartate and asparagine be converted into upon their degradation? Select all that apply.

fumarate, oxaloacetate

Which amino acids supply carbons for an eventual entry into metabolism as succinyl CoA?

methionine, isoleucine, valine

Which amino acid is hydrolyzed to generate urea and ornithine in the urea cycle?

arginine

What enzyme catalyzes the committed reaction of the urea cycle?

carbamoyl phosphate synthetase I

What is the compound that can act as a suicide inhibitor?

fluorodeoxyuridylate

What is the major site of amino acid degradation in mammals?

liver

Choose the molecule into which the carbon skeletons of 20 fundamental amino acids are not funneled.

malate

What are amino acids that are degraded to acetyl CoA or acetoacetyl CoA called?

ketogenic amino acids

For synthesis of what product is alanine taken up in the liver and converted into pyruvate?

glucose

The α-amino groups of which amino acids can be directly converted into an ammonium ion?

serine and threonine

What amino acid is formed upon degradation of phenylalanine?

tyrosine

All defects in the urea cycle lead to an elevated level of ammonium ion in blood, which is called:

hyperammonemia.

In which cellular compartment does citrulline condense with aspartate, the donor of the second amino group of urea?

cytoplasm

Which amino acids can be ketogenic? Select all that apply.

threonine,tyrosine,lysine

What amino acid can be converted into serine by the enzymatic addition of a hydroxymethyl group?

glycine

Which product synthesized in the urea cycle is a precursor for glucose synthesis?

fumarate

What molecule is dehydrogenated to yield β-methylcrotonyl CoA in the degradation of leucine?

isovaleryl CoA

In the urea cycle, free NH3 is coupled with carboxyphosphate to form:

carbamic acid.

Choose the component of the DNA chain.

thymidylate

Ammoniotelic organisms excrete excess nitrogen as:

NH4+.

Which prosthetic group is used in deamination reactions catalyzed by dehydratases?

pyridoxal phosphate

The presence of alanine and aspartate aminotransferase in the blood is an indication of:

liver damage.

Which amino acids are glucogenic? Select all that apply.

asparagine, serine, methionine, valine

Allopurinol is used to treat gout and is an inhibitor of the enzyme

xanthine oxidase.

What is a normal blood value for aspartate aminotransferase activity?

40–125 units/L

How many amino acids are classified as solely glucogenic?

14

Deficiency of what vitamin is indicated by methylmalonic acid accumulation?

B12

In the urea cycle, the second nitrogen of urea enters the cycle in the form of:

aspartate.

Uricotelic organisms release nitrogen as:

uric acid.

What enzymes catalyze nearly all cleavages of aromatic rings in biological systems?

dioxygenases

Which amino acid is a metabolite in the urea cycle but is not used as a building block of proteins? Select all that apply.

ornithine, citrulline, argininosuccinate