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Example Questions
Example Question #12 : Protein Catabolism
Which of the following statements is false regarding catabolic pathways?
Catabolic reactions are the opposite of anabolic reactions
Catabolic pathways have a net consumption of ATP
The citric acid cycle is a catabolic pathway
Catabolic pathways have a net release of energy
Catabolic pathways liberate smaller molecules from larger ones
Catabolic pathways have a net consumption of ATP
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 #2 : Other Protein Catabolism Concepts
What is the purpose of the urea cycle?
Concentration of digestive byproducts in the renal tubules for excretion
Synthesis of urea, a necessary part of renal acid/base balance
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
Conversion of ammonia to urea so that it can be excreted in the urine
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 #1 : Other Protein Catabolism Concepts
Where does the urea cycle occur?
Primarily in the kidney, secondarily in the duodenum
Exclusively in the kidney
Primarily in the kidney, secondarily in the liver
Primarily in the liver, secondarily in the kidney
Primarily in the liver, secondarily in the kidney
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 #2 : Other Protein Catabolism Concepts
In the urea cycle, which of the following amino acids condenses with citrulline, yielding argininosuccinate?
Aspartic acid
Arginine
Asparagine
Glutamic acid
Ornithine
Aspartic acid
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 #1 : Other Protein Catabolism Concepts
During the urea cycle, which enzyme catalyzes the rate-limiting step in the mitochondria?
Glucose-6-phosphate dehydrogenase
Citrate synthase
Triose phosphate isomerase
Phosphofructokinase (PFK)
Carbamoyl phosphate synthase
Carbamoyl phosphate synthase
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 #745 : Biochemistry
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
I, II, III, and IV
II and III
I and IV
III and IV
I, III, and IV
I, III, and IV
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 #742 : Biochemistry
All of the following are intermediate molecules in the urea cycle except __________.
arginosuccinate
ornithine
arginine
citrulline
citrate
citrate
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 #22 : Protein Catabolism
Carbomyl phosphate is a molecule that can enter into the urea cycle. It is formed from the coupling of what two molecules?
and
and
and
and
and
and
Free and bicarbonate can come together to form carbomyl phosphate which can then enter into the urea cycle.
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