Biochemistry II (Chem 4420) Name______________________

Exam II May 14, 1999

1. Uniformly labelled (every possible H was replaced with ³H) ³H-Palmitic acid (16:0) was oxidized in liver mitochondria under aerobic conditions. The amount of radioactivity in the isolated product (acetic acid, which was derived from acetyl CoA) contained only a small percentage of the original radioactivity.
1. (10 points) Give the reactions involved in fatty acid metabolism to yield acetyl-CoA.
2. (5 points) Where did the rest of the radioactivity go? What molecule(s) would you expect to be labelled?



2. Dr. Science needed to make ¹⁴C labelled palmitate. Dr. Science used fully functional acetylCoA carboxylase and fatty acid synthase; and then carefully added all of the cofactors, NADPH, ¹⁴CO₂ and unlabelled acetyl CoA. Unfortunately the product, palmitic acid, had no radioactivity.
1. (10 points) Give all of the reactions that are involved in the synthesis of palmitate.
2. (5 points) Explain the above results.
3. (5 points) What combination of labelled and unlabelled substrates and enzymes should be used in order to have the product (palmitic acid) labelled only on carbon-16. (Recall that fatty acids are numbered starting from the carboxylic acid.)



3. Elephant seals are sea mammals that obtain all of their water via metabolism. Their diets consist mainly of squid, and delicious morsels have a very high fat content. In addition to using stored fat for insulation, they also use fat stores as a source of water.



1. ( 10 points) What are the specific reactions that produce water
2. (10 points) How many moles of water are generated per mole of palmitate? (Your reasoning is the important part of this answer. Please demonstrate how you determined this number.)
3. (10 points) How many liters of water can be obtained from -oxidation of 5 lbs of palmitic acid? (The density of water is 1 g/mL.)

Part II: take home and complete. Please bring your completed exam to class on Monday, May 17^th at 10:10. Using a word processor will brighten the day of your instructor!

1. If there are no carbohydrates in the diet, mammals use fatty acids as a source of fuel. A potentially severe side-effect of this type of diet is the accumulation of ketone bodies. (The brain can not use fatty acids as a source of fuel, it must have glucose or ketone bodies as energy sources.)



1. ( 5 points) Why is there an increase in the blood levels of ketone bodies? Why are high levels of ketones dangerous?

1. (5 points) Why can't the liver use ketone bodies for energy?

1. (10 points) Explain (in detail) why fatty acids with an even number of carbons can not be used to synthesize glucose. Also explain why fatty acids with an odd number of carbons can be used to make glucose. Be sure to include relevant biochemical reactions to support your answer.



2. Fat metabolism (breakdown and synthesis) is carefully controlled so that the two opposing processes do not operate simultaneously.
1. (10 points) Discuss the control mechanisms of -oxidation and fatty acid synthesis that are responsible for this regulation.
2. ( 5 points) One of the enzymes in fat metabolism is regulated via phosphorylation of a serine residue. If this serine residue is replaced with an alanine in a mutant protein, what effect would this mutation have on fat metabolism?