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Problem 24.1
Starting with acetyl-S-enzyme-1 and malonyl-CoA, how many molecules of acetyl-CoA are needed to synthesize an 18-carbon fatty acid (C18:0)? How many molecules of CO₂ are released in this process?
Problem 24.1
Cholesterol (see structure below) and cholate (a bile acid anion, whose structure is shown on p. 731) are sterols with very similar structures. However, the roles they play in the body are different: Cholate is an emulsifier, whereas cholesterol plays an important role in membrane structure. Identify the small differences in their structures that make them well suited to their jobs in the body. Given their similar structures, can the roles of these molecules be reversed? <IMAGE>
Problem 24.11
Oxygen is not a reactant in the ß oxidation of fatty acids. Can ß oxidation occur under anaerobic conditions? Explain.
Problem 24.12
Identify each lipoprotein described here as either chylomicron, HDL, LDL, or VLDL.
a. Which lipoprotein has the lowest density? Why?
Problem 24.12
Identify each lipoprotein described here as either chylomicron, HDL, LDL, or VLDL.
d. Which lipoprotein contains “bad cholesterol” from a vascular disease risk standpoint?
Problem 24.14
One strategy used in many different biochemical pathways is an initial investment of energy early on and a large payoff in energy at the end of the pathway. How is this strategy utilized in the catabolism of fats?
Problem 24.18
Compare the differences between ß oxidation and fatty acid synthesis (lipogenesis). Are these pathways the reverse of each other?
Problem 24.19
Why do lipids make you feel full for a long time after a meal?
Problem 24.21
What is the purpose of bile acids in lipid digestion?
Problem 24.23
Write the equation for the hydrolysis of a triacylglycerol composed of stearic acid, oleic acid, and linoleic acid by pancreatic lipase.
Problem 24.26
What is the origin of the triacylglycerols transported by very low-density lipoproteins?
Problem 24.28
How is cholesterol transported around the body? When it leaves the liver, what is its destination and use?
Problem 24.29
The glycerol derived from lipolysis of triacylglycerols is converted into glyceraldehyde 3-phosphate, which then enters into step 6 of the glycolysis pathway. What further transformations are necessary to convert glyceraldehyde 3-phosphate into pyruvate?
Problem 24.3
How are long-chain fatty acids released from triacylglycerides transported through the bloodstream?
Problem 24.32
How many molecules of acetyl-CoA result from catabolism of 1 molecule of glyceryl trilaurate?
(Hint: See Worked Example 24.3 and don’t forget glycerol.)
Problem 24.39
Why is the stepwise oxidation of fatty acids called ß oxidation?
Problem 24.45
Arrange these following four molecules in increasing order of their biological energy content (per mole):
a. Sucrose
b. Myristic acid, CH₃(CH₂)₁₂COOH
c. Glucose
d. Capric acid, CH₃(CH₂)₈COOH
Problem 24.48
Write the equation for the final step in the catabolism of any fatty acid with an even number of carbons.
Problem 24.5
How many molecules of acetyl-CoA are produced by catabolism of the following fatty acids, and how many ß oxidations are needed?
a. Palmitic acid, CH₃(CH₂)₁₄COOH
Problem 24.53
What causes acetone to be present in the breath of someone with uncontrolled diabetes?
Problem 24.58
Name the starting material for fatty acid synthesis.
Problem 24.6
Look back at the reactions of the citric acid cycle (Figure 21.8) and identify the three reactions in that cycle that are similar to the first three reactions of the ß oxidation of a fatty acid. <IMAGE>
Problem 24.6
How many rounds of the lipogenesis cycle are needed to synthesize stearic acid, C17H35COOH?
Problem 24.64
Consuming too many carbohydrates causes deposition of fats in adipose tissue. How does this happen?
Problem 24.65
Why are extra calories consumed as carbohydrates stored as fat and not as glycogen?
Problem 24.68
Lipoproteins that transport lipids from the diet are described as exogenous. Those that transport lipids produced in metabolic pathways are described as endogenous. Which of the following lipoproteins transports exogenous lipids and which transports endogenous lipids?
a. Low-density lipoprotein (LDL)
b. Chylomicrons
Problem 24.7
High blood-cholesterol levels are dangerous because of their correlation with atherosclerosis and consequent heart attacks and strokes. Is it possible to eliminate all cholesterol from the bloodstream by having a diet that includes no cholesterol? Is it desirable to have no cholesterol at all in your body? Explain your answer.
Problem 24.72
A low-fat diet of pasta, bread, beer, and soda can easily lead to an increase in weight. The increase is stored triacylglycerols in adipocytes. Explain the weight increase and why the excess carbohydrate is stored as fat.
Problem 24.72
How many moles of ATP are produced by the complete oxidation of 1 mol of myristic acid?
Problem 24.8
Which of the following classifications apply to the formation of 3-hydroxybutyrate from acetoacetate?
a. Condensation
b. Hydrolysis
c. Oxidation
d. Reduction
