Biochemistry : Other Protein Catabolism Concepts

Study concepts, example questions & explanations for Biochemistry

varsity tutors app store varsity tutors android store

Example Questions

Example Question #13 : Protein Catabolism

Which of the following statements is false regarding catabolic pathways?

Possible Answers:

Catabolic pathways have a net release of energy

The citric acid cycle is a catabolic pathway

Catabolic pathways liberate smaller molecules from larger ones

Catabolic pathways have a net consumption of ATP

Catabolic reactions are the opposite of anabolic reactions

Correct answer:

Catabolic pathways have a net consumption of ATP

Explanation:

Both catabolic and anabolic reactions are metabolic reactions. The difference is that catabolism is when complex molecules break down into simpler molecules, and anabolism is when simpler molecules are combined to form complex molecules. ATP (adenosine triphosphate) is used to store and transport energy in cells. There is a major difference in how ATP is used in catabolic and anabolic reactions. Anabolic reactions require energy input, and result in a net consumption of ATP. Catabolic reactions produce energy and results in a net synthesis of ATP. Therefore, catabolic pathways do not have a net consumption of ATP.

Example Question #1 : Other Protein Catabolism Concepts

What is the purpose of the urea cycle?

Possible Answers:

Synthesis of urea, a necessary part of renal acid/base balance

Concentration of digestive byproducts in the renal tubules for excretion

Conversion of urea into ammonia so that it can be excreted in the urine

Conversion of ammonia to urea so that it can be excreted in the urine

Correct answer:

Conversion of ammonia to urea so that it can be excreted in the urine

Explanation:

The urea cycle is vital to the excretion of ammonia, a harmful byproduct of amino acid breakdown. Via a series of enzymatic changes, ammonia is converted to urea, which can be excreted into the urine. 

Example Question #15 : Protein Catabolism

Where does the urea cycle occur?

Possible Answers:

Exclusively in the kidney

Primarily in the kidney, secondarily in the liver

Primarily in the liver, secondarily in the kidney

Primarily in the kidney, secondarily in the duodenum

Correct answer:

Primarily in the liver, secondarily in the kidney

Explanation:

The urea cycle occurs primarily in the liver, and to a lesser extent in renal cells. There is no urea conversion performed by the small intestine. 

Example Question #16 : Protein Catabolism

In the urea cycle, which of the following amino acids condenses with citrulline, yielding argininosuccinate?

Possible Answers:

Aspartic acid

Glutamic acid

Arginine

Ornithine

Asparagine

Correct answer:

Aspartic acid

Explanation:

Arginine is the amino acid in the cycle that is converted to urea and ornithine via the enzyme arginase, and is one of the products of the lysis of argininosuccinate. Glutamic acid plays a different role in the cycle; it loses its amino group to the synthesis of carbamoyl phosphate, a precursor of citrulline. Asparagine is not present in the urea cycle, but aspartic acid is. It condenses with citrulline, through the action of the enzyme argininosuccinate synthase and ATP, to produce argininosuccinate.

Example Question #21 : Protein Catabolism

During the urea cycle, which enzyme catalyzes the rate-limiting step in the mitochondria?

Possible Answers:

Citrate synthase

Triose phosphate isomerase

Phosphofructokinase (PFK)

Carbamoyl phosphate synthase

Glucose-6-phosphate dehydrogenase 

Correct answer:

Carbamoyl phosphate synthase

Explanation:

Triose phosphate isomerase catalyzes the isomerization between dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. Glucose-6-phosphate dehydrogenase is a regulatory enzyme for the pentose phosphate pathway. Citrate synthase is a regulatory enzyme for the Krebs cycle, catalyzing the synthesis of citrate from acetyl-CoA and oxaloacetate. PFK catalyzes the rate-limiting step in glycolysis.

Example Question #22 : Protein Catabolism

What is the difference between ketogenic and glucogenic amino acids?

I. Ketogenic amino acids are degraded to acetyl-CoA and ketones; glucogenic amino acids can be converted to glucose

II. Ketogenic amino acids are alanine and glutamine

III. The ketogenic amino acids are leucine and lysine

IV. Amino acids that are glucogenic and ketogenic are: phenylalanine, tyrosine, tryptophan, isoleucine and threonine

Possible Answers:

I, III, and IV

I and IV

III and IV

I, II, III, and IV

II and III

Correct answer:

I, III, and IV

Explanation:

Ketogenic amino acids are degraded to Acetyl Coenzyme A (CoA) and ketones; glucogenic amino acids can be converted to glucose. Amino acids that are both ketogenic and glucogenic can be metabolized to both glucose and ketone bodies. Purely ketogenic aminoacids are leucine and lysine. Amino acids that are glucogenic and ketogenic are: phenylalanine, tyrosine, tryptophan, isoleucine and threonine. All the other amino acids are glucogenic.

Example Question #23 : Protein Catabolism

All of the following are intermediate molecules in the urea cycle except __________.

Possible Answers:

citrulline

citrate

ornithine

arginine

arginosuccinate

Correct answer:

citrate

Explanation:

In the urea cycle, carbomyl phosphate first combines with the molecule ornithine. This forms citrulline. Citrulline then reacts with aspartate to form arginosuccinate. Fumarate dissociates from arginosuccinate forming arginine, and then the addition of water forms urea and ornithine once again to complete the cycle. Citrate is not involved in this cycle, it is however in the Krebs cycle.

Example Question #2 : Other Protein Catabolism Concepts

Carbomyl phosphate is a molecule that can enter into the urea cycle. It is formed from the coupling of what two molecules?

Possible Answers:

 and 

 and 

 and

 and 

 and 

Correct answer:

 and

Explanation:

Free  and bicarbonate  can come together to form carbomyl phosphate which can then enter into the urea cycle.

Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: