Chapter 16

Calculate the ATP yield from oxidation of palmitic acid, taking into account the energy needed to activate the fatty acid and transport it into mitochondria. Do the same for stearic acid, linoleic acid, and oleic acid.

Calculate the number of ATPs generated by the complete metabolic oxidation of tripalmitin (tripalmitoylglycerol). Hydrolysis of the triacylglycerol occurs at the cell surface. Consider the energy yield from catabolism of glycerol, as well as from the fatty acids. Calculate the ATP yield per carbon atom oxidized, and compare it with the energy yield from glucose.

Write a balanced equation for the complete metabolic oxidation of each of the following. Include \(\mathrm{O}_{2}, \mathrm{ADP}\), and \(\mathrm{P}_{\mathrm{i}}\) as reactants and ATP, \(\mathrm{CO}_{2}\), and \(\mathrm{H}_{2} \mathrm{O}\) as products. (a) Stearic acid (c) Palmitic acid (b) Oleic acid (d) Linoleic acid

2-Bromopalmitoyl-CoA inhibits the oxidation of palmitoyl-CoA by isolated mitochondria but has no effect on the oxidation of palmitoylcarnitine. What is the most likely site of inhibition by 2-bromopalmitoyl-CoA?

When the identical subunits of chicken liver fatty acid synthase are dissociated in vitro, all of the activities can be detected in the separated subunits except for the \(\beta\)-ketoacyl synthase reaction and the overall synthesis of palmitate. Explain these observations.

Describe a pathway whereby some of the carbon from a fatty acid with an odd- numbered carbon chain could undergo a net conversion to carbohydrate.

As low-carbohydrate diets have experienced a dramatic increase in popularity, arguments have been made that glucose can be made from odd-chain fatty acids. Based on the metabolism of such molecules, what quantity of a C-19 fatty acid would be required to produce \(1 \mathrm{~g}\) of glucose? Considering that odd- chain fatty acids make up approximately \(1 \%\) of the fat in our diet, what quantity of fatty acids would be needed to produce \(1 \mathrm{~g}\) of glucose?

A dialyzed pigeon liver extract will catalyze the conversion of acetyl-CoA to palmitate and CoASH if supplied with \(\mathrm{Mg}^{2+}, \mathrm{NADPH}, \mathrm{ATP}^{-\mathrm{HCO}_{3}-}\), and citrate. (a) If \(\mathrm{H}^{14} \mathrm{CO}_{3}^{-}\)is supplied, what compounds will become labeled (permanently or transiently) during the course of the reaction? In what compounds will \({ }^{14} \mathrm{C}\) accumulate? (b) Explain the role of citrate in this reaction.

What would be the effect on fatty acid synthesis of an increase in intramitochondrial oxaloacetate level? Briefly explain your answer.

Discuss the metabolic rationale for phosphorylation of acetyl-CoA carboxylase by AMP-activated protein kinase (AMPK) and cyclic AMP-dependent protein kinase (PKA).

Describe the probable effect in adipocytes of insulin-stimulated uptake of glucose into these cells.

Phosphatidylserine (PS) is considered to be an intermediate in the biosynthesis of phosphatidylethanolamine (PE) in E. coli, yet PS is not found in appreciable amounts among \(E\). coli membrane phospholipids. Because PS must be present in the membrane to serve as an intermediate, how might you explain its failure to accumulate to a significant extent? What kinds of experiments could test your proposed explanation?

If mevalonate labeled with \({ }^{14} \mathrm{C}\) in the carboxyl carbon were administered to rats, which carbons of cholesterol would become labeled?

Identify a pathway for utilization of the four carbons of acetoacetate in cholesterol biosynthesis. Carry your pathway as far as the rate-determining reaction in cholesterol biosynthesis.

cis-Vaccenate is an 18-carbon unsaturated fatty acid abundant in \(E\). coli membrane lipids. Propose a metabolic route for synthesis of this fatty acid, in light of the fact that stearic acid, the \(\mathrm{C}_{18}\) saturated analogous fatty acid, is virtually absent from \(E\). coli lipids.