© 2000 Prentice Hall. All rights reserved.

Dr. Glaser's "Chemistry is in the News"
To Accompany Bruice, Organic Chemistry, 3/e.
Chapter 23. The Organic Mechanisms of the Coenzymes. Metabolism.


For each of the following questions, please refer to the following article:
PANEL REVISES VITAMIN B RECOMMENDATIONS
by Damaris Christensen (Medical Tribune News Service, April 8, 1998)


Editorial Comments

This article deals with two vitamins. Let's begin by making sure we know the structures of these compounds. You can look them up in the book, or you can refresh your memories using Chemfinder. Note that the ChemFinder has entries for both "Folic Acid" and "Folic acid". Look at the entry for "Folic Acid"; it is more complete. Make sure to recognize the building blocks of folic acid: glutamic acid, para-aminobenzoic acid, and 2-amino-4-oxo-6-methylpterin. The structure of vitamin B12 also can be found with ChemFinder.

The Institute of Medicine (IOM), a federal advisory agency, recently published recommendations concerning the B vitamins. The recommendations include: (1) Women who are considering pregnancy should consume 400 micrograms of folate or folic acid, also called vitamin B, vitamin B11 or vitamin M, in excess of the daily intake due to a regular diet. This measure is to avoid neural tube defects. (2) Older people should use supplements to make sure they meet the recommended 2.4 milligrams of B12 per day. Deficiency in vitamin B12 leads to pernicious anemia.

What makes this announcement special? There are two reasons. This is the first time that the Institute of Medicine has recommended that large groups of people help meet their daily nutritional needs through supplements or fortified foods. Secondly, the announcement emphasizes that a good balance is important. Not only did the panel recommend to meet a certain minimal daily dosage, but the recommendation also asks for staying within certain recommended maximal amounts. Specifically, the IOM committee recommended that people eat no more than 1,000 micrograms, or 1 milligram, of folate daily, in large part because high levels may mask symptoms of vitamin B12 deficiency.



Pertinent Text References
Chapter 23. The Organic Mechanisms of the Coenzymes. Metabolism.
Table 23.1 The Vitamins, Their Coenzymes, and Their Chemical Function.
Chapter 23.7 Coenzyme B12: Vitamin B12
Chapter 23.8 Tetrahydrofolate: Folic Acid



Questions

Question 1: Let's make sure we all have an idea about the quantities of vitamins we are talking about. How many micrograms make one gram? How many milligrams make one gram?

Answer 1: 1,000,000 microgram = 1,000 milligram = 1 gram.



Question 2: Which coenzyme is produced from the vitamin precursor folic acid? How does the structure of this coenzyme differ from folic acid? What is the function of this coenzyme?

Answer 2: Tetrahydrofolate, THF. Four H-atoms are added across the two C=N double bonds in the 6-membered ring; they are added to atoms 5 - 8. The coenzyme THF is used to catalyze the donation of a group containing one carbon (methyl, methylene, formyl groups).



Question 3: Briefly explain the function of the enzyme "thymidylase synthase" and the role of its cofactor N5,N10-methylene-THF.

Answer 3: Bruice, 3/e, Chapter 23, p. 1024.



Question 4: Using the example of the enzyme "thymidylase synthase", briefly explain the concept of cancer chemotherapy based on mechanism-based suicide inhibitors.

Answer 4: Bruice, 3/e, Chapter 23, p. 1025.



Question 5: Describe the human deficiency diseases "anemia", "pernicious anemia", and "megaloblastic anemia".

Answer 5: The answers from the BRITANNICA are as follows: Anemia (Gk anaimia bloodlessness): A condition in which the blood is deficient in red blood cells, in hemoglobin, or in total volume. Megaloblast: A large erythroblast that appears in the blood esp. in pernicious anemia. Pernicious anemia: A severe megaloblastic anemia marked by a progressive decrease in the number of red blood cells and by pallor, weakness, and gastrointestinal and nervous disturbances and associated with malabsorption of vitamin B12 due to the absence of intrinsic factor.



Chemistry & Society.
We discussed recommendations by the Institute of Medicine. What is the Institute of Medicine and why should we accept and follow its recommendations? The Institute of Medicine is part of The National Academies, Advisors to the Nation on Science, Engineering and Medicine. Browse the website of the The National Academies and learn about their history, their goals and their organization.