This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Major form of folic acid to transfer one carbon is 
Select and explain. 
A. Methylene THF, B. Formyl THF, C. Methyl THF, D. All
A: Methylene THF
Answer: A: Methylene THF 
Explanation: The folic acid is first reduced to 7,8-dihydrofolic acid and fuher reduced to 5,6,7,8-tetrahydrofolic acid (THFA) (Fig. 34.17). Both reactions are catalyzed by NADPH dependent folate reductase. B. TThe folic acid is first reduced to 7,8-dihydrofolic acid and fuher reduced to 5,6,7,8-tetrahydrofolic acid (THFA) (Fig. 34.17). Both reactions are catalyzed by NADPH dependent folate reductase.The THFA is the carrier of one-carbon groups. One carbon compound is an organic molecule that contains only a single carbon atom. The following groups are one carbon compounds: i. Formyl (-CHO) ii. Formimino (-CH=NH) iii. Methenyl (-CH=) iv. Methylene (-CH2-) v. Hydroxymethyl (-CH2OH) vi. Methyl (-CH3).he THFA is the carrier of one-carbon groups. One carbon compound is an organic molecule that contains only a single carbon atom. The following groups are one carbon compounds: i. Formyl (-CHO) ii. Formimino (-CH=NH) iii. Methenyl (-CH=) iv. Methylene (-CH2-) v. Hydroxymethyl (-CH2OH) vi. Methyl (-CH3).Ref: DM Vasudevan - Textbook of Biochemistry, 6th edition, page no: 401