PROBLEM SET 8. Fatty Acid Oxidation

 

The first seven Problem Sets dealt with the fundamental principles you need to predict the products of any biochemical reaction. You now have the tools you need to construct complicated metabolic pathways from a few given facts. The rest of the course deals with these pathways.

Each Monday, I will post a new Problem Set. I will also post the Answers to the previous Problem Set. These are my answers.  Yours may be different, but they  should be derived from the same principles. The Problem Set numbers correspond to chapters in CBM where you will find a detailed discussion. However, it is very important that you WRITE OUT your answers before  you consult any reference material including CBM. Remember, our objective is to predict the product(s) of a reaction logically using the rules of electron pushing.

Given: Fatty acids with an even number of carbon atoms are oxidized to acetyl-CoA.

1. Predict the intermediates in this pathway.

HINT: “In solving a problem of this sort, the grand thing is to be able to reason backwards. That is a very useful accomplishment, and a very easy one, but people do not practice it much.” Sherlock Holmes (From A Study in Scarlet by A. Conan Doyle)

2. Write two different mechanisms for the initial reaction. From a metabolic point of view, which is more likely?

3. Look in the databases( http://www.chem.qmul.ac.uk/iubmb/ and (http://www.brenda-enzymes.info/ )  to see if you can find the enzymes required for the reactions you have written.

4. How many ATPs are produced by each turn of the oxidation spiral?

5. How much energy is produced by oxidation of stearic acid to acetyl-CoA?

6.Fatty acyl dehydrogenase produces the trans isomer. What can you conclude about how the enzyme works?

7. Naturally occurring fatty acids are always cis.  What problem does that present for oxidation of oleic acid (9-cis-octadecenoic acid)?

8. Write two different mechanisms for isomerization of a double bond in a fatty acid. Which of these mechanisms works in the oxidation of oleic acid? (HINT:After you have written the mechanisms,  look for the appropriate enzyme(s).

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