Question 1

The synthetic compound mevinolinic acid,also called lovastatin,is a potent competitive inhibitor of HMG-CoA reductase (hydroxymethylglutaryl-CoA reductase).Predict and explain the effect of this drug on serum cholesterol levels in humans.

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Question 2

Show the structure of isopentenyl pyrophosphate and of dimethylallyl pyrophosphate.Connect with a dotted line the two carbon atoms that will be joined when these two molecules condense to form the 10-carbon intermediate in cholesterol biosynthesis.

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Question 3

Show the reaction that limits the rate of cholesterol synthesis from acetate,indicating the role of any cofactors that participate.

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Question 4

Describe the formation of farnesyl pyrophosphate from activated isoprenyl units.

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Question 5

The synthesis of cholesterol begins with the condensation of a four-carbon unit from _______________ with the two carbons of acetyl-CoA to form a six-carbon derivative.Give its structure,and circle the atoms that originated in the acetyl-CoA.

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Question 6

When a 10-carbon unit and a 5-carbon unit condense to a 15-carbon intermediate in the pathway to cholesterol,the mechanism of condensation is basically different from that of the condensation of two 15-carbon units to the 30-carbon compound squalene.Describe the two condensations in enough chemical detail to illustrate the difference between them.(You should show relevant structures. )

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Question 7

Describe (briefly)two classes of genetic defects in humans that could produce an elevated blood serum cholesterol level.

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Question 8

Show the pathway from acetyl-CoA to mevalonate,indicating the roles of any cofactors.

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Question 9

Describe the process by which cholesterol esters in the bloodstream enter cells.

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Question 10

Explain briefly why we require fats in our diets.

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Question 11

What are plasma lipoproteins? What is their general role in mammalian metabolism?

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Question 12

Sketch the pathway from arachidonate to thromboxanes and explain how aspirin blocks the synthesis of thromboxanes.

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Question 13

Describe briefly the four stages in the pathway from acetyl-CoA to lanosterol.

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Question 14

Describe two basic strategies for activating precursors in the biosynthesis of phospholipids.

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Question 15

Explain the triacylglycerol cycle and how drugs such as rosiglitazone (Avandia)promote this cycle and help lower fatty acid levels in the bloodstream.

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Question 16

Show the two different biosynthetic pathways from phosphatidic acid to phosphatidylcholine.You may use shorthand notation for phosphatidic acid,but name any cofactors required in the path and show where they are involved.

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Question 17

Show the pathway from mevalonate to dimethylallyl pyrophosphate,indicating where any cofactors participate.

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Question 18

Shown below is a molecule of squalene,which is composed of 6 isoprene units.Draw lines to indicate the junctions between the six isoprene units.

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Quiz 21: Lipid Biosynthesis