Question

Patients with hereditary fructose intolerance are deficient in the liver form of the enzyme aldolase. Consumption of fructose leads to a depletion of ATP and \(P\), in the liver, which, in turn, leads to cell damage, Much of the cell damage can be attributed to the inability to maintain normal ion gradients by ATP-dependent pumps. The first step in liver's metabolism of fructose is A. isomerization to glucose. B. phosphorylation to fructose 1,6 -bisphosphate by ATP. C. phosphorylation to fructose 1-phosphate by ATP. D. phosphorylation to fructose 6 -phosphate by ATP. E cleavage by aldolase.

Short answer

Answer: The first step in liver's metabolism of fructose is phosphorylation to fructose 1-phosphate by ATP.

Step-by-step solution

Understand hereditary fructose intolerance and its effects on aldolase

Hereditary fructose intolerance (HFI) is a genetic disorder that affects a person's ability to metabolize fructose (a sugar) properly, due to a deficiency in the liver enzyme aldolase. This enzyme is involved in breaking down fructose into usable energy. Without this enzyme, fructose cannot be efficiently metabolized, leading to harmful effects on the liver cells.

Analyze option A - isomerization to glucose

Isomerization is the process by which one molecule is transformed into another molecule that has the same atoms but in a different arrangement. In this case, option A suggests that fructose is converted to glucose, which is another simple sugar. Although fructose can be converted to glucose through a series of metabolic steps, this is not the first step in fructose metabolism in the liver. So, option A is incorrect.

Analyze option B - phosphorylation to fructose 1,6-bisphosphate by ATP

Phosphorylation is the process of adding a phosphate group to a molecule, usually from ATP (adenosine triphosphate). Fructose 1,6-bisphosphate is an intermediate in glycolysis (glucose metabolism) and is not a direct product of fructose phosphorylation. So, option B is incorrect.

Analyze option C - phosphorylation to fructose 1-phosphate by ATP

The first step in the liver's metabolism of fructose is the phosphorylation of fructose to fructose 1-phosphate by ATP. In the presence of fructokinase, an enzyme in the liver, ATP donates a phosphate group to fructose resulting in fructose 1-phosphate. So, option C is correct.

Analyze options D and E for completeness

Option D suggests that fructose is phosphorylated to fructose 6-phosphate by ATP. This is an intermediate step in glucose metabolism, not the first step in fructose metabolism in the liver. So, option D is incorrect. Option E suggests that fructose is cleaved by aldolase. In the context of HFI, individuals have a deficiency of the aldolase enzyme and are unable to perform this step efficiently. Therefore, this is not the first step in liver fructose metabolism, and option E is also incorrect.

Conclusion

The correct answer is option C: The first step in liver's metabolism of fructose is phosphorylation to fructose 1-phosphate by ATP.