A newborn baby has . Clotting studies demonstrate an elevated prothrombin time. An abnormality of which of the following biochemical processes is likely present in this patient?

A. Conversion of homocysteine to methionine
B. Conversion of methylmalonyl CoA to succinyl CoA
C. Degradation of cystathionine
D. Formation of gamma-carboxyglutamate residues
E. Hydroxylation of proline

Is it related to Vit K synthesis?

The correct answer is D. Deficiency of vitamin K produces a clotting disorder characterized by an elevated prothrombin time and easy bleeding, particularly in neonates (hemorrhagic disease of the newborn). The biochemical basis for this hemorrhagic tendency is that glutamate residues on Factors II (Thrombin), VII, IX, and X must be converted to gamma-carboxyglutamate residues (in a vitamin K-requiring reaction) for optimal activity.
The conversion of homocysteine to methionine (choice A) requires vitamin B12.

Conversion of methylmalonyl CoA to succinyl CoA (choice B) requires vitamin B12.

Degradation of cystathionine (choice C) requires vitamin B6.

Hydroxylation of proline (choice E) requires vitamin C. Vitamin C deficiency can cause easy bruising, but will not prolong the prothrombin time.