Biochemistry at The Biology Project

B12/Folate Problem set

Question 3: Effect of folate-B12 disruptions on neural membranes

Tutorial to help answer the question

Which important enzyme cofactor, crucial to the integrity of neural membranes, is produced from methionine?

A. homocysteine
C. tetrahydrobiopterin
D. S-adenosylmethionine
E. glutathione


SAM I am!

Fig. 3 - S-adenosyl methionine: an intermediate and so much more!

Aside from its role as an amino acid component of proteins, methionine can also be bound to an adenosyl group to form S-adenosyl methionine, or SAM, in reaction (a) [don't worry about the enzyme name]. SAM, in turn, donates this methyl group to important recipients in several reactions (grouped as "b"). Clinical observations suggest that neural membrane lipids such as phosphatidylcholine or spingomyelin are particularly dependent on the presence of SAM for their synthesis. Indeed, in a dietary deficiency of either folate or B12, biosynthesis of these important components of myelin is disrupted, leading to various neurological symptoms. So, B12 is crucial for formation of SAM, but it also has another role to play...

[Problem 3] [Answer] [Problem 4]

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