Question 1

Conversion of ammonia to carbamoyl phosphate in mitochondria consumes how many ATP equivalents?

Accepted Answer

The conversion of ammonia to carbamoyl phosphate in mitochondria consumes two ATP equivalents. This reaction is catalyzed by the enzyme carbamoyl phosphate synthetase and requires two ATP molecules to provide phosphate groups for the conversion of ammonia to carbamoyl phosphate.

Question 2

Which reaction associated with the urea cycle occurs in the cytosol?

Accepted Answer

The synthesis of arginosuccinate occurs in the cytosol as part of the urea cycle.

Question 3

Carbamoyl phosphate synthase I is allosterically activated by what molecule?

Accepted Answer

Carbamoyl phosphate synthase I is activated by N-acetylglutamate, which is a small molecule that is synthesized from glutamate and acetyl-CoA.

Question 4

Which statement is FALSE regarding pepsin?

Accepted Answer

Pepsin is highly active at a low pH, specifically around 2.0-2.5 in the stomach. It is classified as a hydrolase and is secreted in response to protein ingestion. It has a specificity for cleavage at aromatic amino acids, particularly phenylalanine, tryptophan, and tyrosine. However, pepsin activation occurs through reversible cleavage of its inactive precursor, pepsinogen, rather than irreversible covalent modification.

Question 5

Which amino acid can be imported into mitochondria from the cytosol in liver cells?

Accepted Answer

All of the listed amino acids, glutamine, glutamate, and ornithine, can be imported into mitochondria from the cytosol in liver cells. These amino acids play crucial roles in various metabolic pathways, including the urea cycle and amino acid metabolism, which are active in liver mitochondria.

Question 6

Which cofactor is typically required in transamination reactions?

Accepted Answer

Pyridoxal-phosphate is a cofactor that is typically required in transamination reactions. It helps to transfer an amino group from an amino acid to a keto acid, ultimately forming a new amino acid and a new keto acid. Without this cofactor, transamination reactions cannot take place. The other cofactors listed (coenzyme Q, biotin, thiamin pyrophosphate, and nicotinamide adenine dinucleotide) are involved in other metabolic processes.

Question 7

Nitrogen from protein is eliminated as what compound in animals?

Accepted Answer

Nitrogen from protein metabolism is primarily excreted as ammonia (NH3) in aquatic animals due to its high solubility in water, and as urea in terrestrial animals, where water conservation is more critical. This makes both ammonia and urea correct answers.

Question 8

Which statement is FALSE for uric acid?

Accepted Answer

Uric acid is a product of both protein and nucleic acid catabolism. It is the major means of nitrogen elimination in birds and is produced in humans as a result of high-protein diets. Uric acid is a purine base.

Question 9

Which amino acid can be considered to be both glucogenic and ketogenic?

Accepted Answer

Threonine and isoleucine are both glucogenic and ketogenic amino acids. Glucogenic amino acids can be converted into glucose through gluconeogenesis, while ketogenic amino acids can be converted into ketone bodies. Threonine can form both pyruvate and acetyl-CoA, which can enter the Krebs cycle and ultimately lead to glucose production, as well as ketone body production. Isoleucine can be converted into both acetyl-CoA and succinyl-CoA, which have the same potential fate as threonine. Both of these amino acids have carbon skeletons that can be used for both energy production and glucose synthesis.

Question 10

Which hormone is triggered by the entry of acidic stomach content into the intestine?

Accepted Answer

The hormone triggered by acidic stomach content entering the intestine is secretin. Secretin is released from the duodenum in response to low pH and stimulates the pancreas to release bicarbonate to neutralize the acidity of the stomach acid entering the small intestine. Gastrin is released in response to food in the stomach and stimulates the release of stomach acid. Insulin is released from the pancreas in response to high blood sugar levels. Cholecystokinin is released from the small intestine in response to the presence of fat and protein, and it stimulates the release of bile from the gallbladder and digestive enzymes from the pancreas.

Question 11

Deamination of most amino acids in the liver is accompanied by the conversion of:

Accepted Answer

The answer of Deamination of most amino acids in the...

Question 12

Which amino acid is used to transport nitrogen to the liver?

Accepted Answer

Alanine and glutamine are both used to transport nitrogen to the liver. Alanine carries nitrogen from muscle tissue to the liver, where it can be converted into glucose. Glutamine serves a similar role, transporting nitrogen to the liver but is also important for immune system function and intestinal health.

Question 13

Which statement is TRUE regarding glutamine synthetase?

Accepted Answer

Glutamine synthetase is classified as a ligase because it catalyzes the joining of two molecules (glutamate and ammonia) with the concomitant hydrolysis of ATP. An intermediate in this reaction is indeed an acyl phosphate, which is formed from the initial ATP-dependent phosphorylation of glutamate.

Question 14

Which hormone is triggered by the entry of protein into the stomach?

Accepted Answer

Gastrin is the hormone that is triggered by the entry of protein into the stomach. It stimulates the release of gastric acid and pepsinogen, which are necessary for protein digestion.

Question 15

In which pair of compounds is the second molecule produced by the deamination of the first molecule?

Accepted Answer

Deamination is the removal of an amino group from a molecule. In the given options, aspartic acid is deaminated to form oxaloacetate, glutamine is deaminated to form glutamate, and alanine is deaminated to form pyruvate. Therefore, all of the answers are correct.

Question 16

What processes are associated with the glucose-alanine cycle?

Accepted Answer

The glucose-alanine cycle involves multiple processes including gluconeogenesis in the liver, glutamate synthesis in both muscle and the liver, and glucose export from the liver. Therefore, option D, "All of the answers are correct," is the best choice.

Question 17

A possible product of isoleucine catabolism is:

Accepted Answer

Isoleucine catabolism can lead to the formation of acetyl-CoA and succinyl-CoA, as well as the conversion to F1F1F1S1F1F1F10-keto isoleucine (F1F1F1S1F1F1F10-keto-F1F1F1S1F1F1F10-methylvalerate). Therefore, all of the answer choices are correct.

Question 18

Which statement is FALSE regarding pyridoxal phosphate?

Accepted Answer

All the statements about pyridoxal phosphate are true. It is essential in aminotransferase reactions, can form covalent bonds with lysine residues and some intermediates, and carries both positive and negative formal charges.

Question 19

Which reaction is a hydrolysis reaction?

Accepted Answer

The conversion of arginine into urea and ornithine by arginase and the conversion of glutamine into glutamate by glutamase both involve the addition of water molecules to break down larger molecules. This is a characteristic of hydrolysis reactions. The conversion of tyrosine into phenylalanine by phenylalanine hydroxylase does not involve the addition of water and is not a hydrolysis reaction.

Question 20

What enzyme classes are responsible for interconverting glutamate and $\alpha$-ketoglutarate?

Accepted Answer

Glutamate and -ketoglutarate are interconverted by transaminases, which are transferases.

Quiz 18: Amino Acid Oxidation and the Production of Urea

Conversion of ammonia to carbamoyl phosphate in mitochondria consumes how many ATP equivalents?

Which reaction associated with the urea cycle occurs in the cytosol?

Carbamoyl phosphate synthase I is allosterically activated by what molecule?

Which statement is FALSE regarding pepsin?

Which amino acid can be imported into mitochondria from the cytosol in liver cells?

Which cofactor is typically required in transamination reactions?

Nitrogen from protein is eliminated as what compound in animals?

Which statement is FALSE for uric acid?

Which amino acid can be considered to be both glucogenic and ketogenic?

Which hormone is triggered by the entry of acidic stomach content into the intestine?

Deamination of most amino acids in the liver is accompanied by the conversion of:

Which amino acid is used to transport nitrogen to the liver?

Which statement is TRUE regarding glutamine synthetase?

Which hormone is triggered by the entry of protein into the stomach?

In which pair of compounds is the second molecule produced by the deamination of the first molecule?

What processes are associated with the glucose-alanine cycle?

A possible product of isoleucine catabolism is:

Which statement is FALSE regarding pyridoxal phosphate?

Which reaction is a hydrolysis reaction?

What enzyme classes are responsible for interconverting glutamate and $\alpha$ -ketoglutarate?

Quiz 18: Amino Acid Oxidation and the Production of Urea

Conversion of ammonia to carbamoyl phosphate in mitochondria consumes how many ATP equivalents?

Which reaction associated with the urea cycle occurs in the cytosol?

Carbamoyl phosphate synthase I is allosterically activated by what molecule?

Which statement is FALSE regarding pepsin?

Which amino acid can be imported into mitochondria from the cytosol in liver cells?

Which cofactor is typically required in transamination reactions?

Nitrogen from protein is eliminated as what compound in animals?

Which statement is FALSE for uric acid?

Which amino acid can be considered to be both glucogenic and ketogenic?

Which hormone is triggered by the entry of acidic stomach content into the intestine?

Deamination of most amino acids in the liver is accompanied by the conversion of:

Which amino acid is used to transport nitrogen to the liver?

Which statement is TRUE regarding glutamine synthetase?

Which hormone is triggered by the entry of protein into the stomach?

In which pair of compounds is the second molecule produced by the deamination of the first molecule?

What processes are associated with the glucose-alanine cycle?

A possible product of isoleucine catabolism is:

Which statement is FALSE regarding pyridoxal phosphate?

Which reaction is a hydrolysis reaction?

What enzyme classes are responsible for interconverting glutamate and α\alphaα -ketoglutarate?

What enzyme classes are responsible for interconverting glutamate and $\alpha$ -ketoglutarate?