BIOC 3021 Study Guide - Midterm Guide: Ketone, Fatty Acid Synthase, Acetoacetic Acid

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16 Sep 2016

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Introduction to lipids and lipoproteins: lipids come from the diet, are stored as triglycerides in adipose tissue, and undergo fatty acid synthesis. Fatty acid activation: fatty acids are activated through a reaction catalyzed by acyl-coa synthetase. In this reaction a fatty acid is converted to acyl coa, and 2 p i and amp are also produced. Fatty acid transport: lipases produce fatty acids in cytosol. Fatty acids are transported through the mitochondrial membrane as carnitine derivatives. Once in the mitochondria fatty acids are returned to coa derivatives. Formation of carnitine derivatives occurs by combining acyl coa and carnitine to create a single acyl carnitine molecule and hs-coa. Oxidation: similar steps to those of the krebs cycles, with some different molecules. Acyl-coa dehydrogenase is used rather than succinate dehydrogenase in the oxidation with fad. Coa hydratase is used rather than fumarase in the addition of water. 3-l-hydroxyacyl-coa dehydrogenase is used rather than l-malate dehydrogenase in the oxidation with nad +.

Related Questions

B-Oxidation of Trans Fats ljnsaturated fats with trans double bonds are commonly referred to as "trans fats." There has been much discussion about the effects of dietary trans fats on health. In their investigations of the effects of trans fatty acid metabolism on health, Yu and col- Ieagues (2004) showed that a model trans fatty acid was processed differently from its cis isomer. They used three related l8-carbon fatty acids to explore the difference in F oxidation between cis and trans isomers of the same-size fatty acid.

(a) Why did Yu and colleagues need to use CoA deriva- tives rather than the free fatty acids in these experiments?

(b) Why were no lower molecular weight CoA derivatives found in the reaction with stearoyl-CoA?

(c) How many rounds of B oxidation would be required to convert the oleoyl-CoA and the elaidoyl-CoA to cd,s-L5- tetradecenoyl- C oA and trans-A5-tetrade cenoyl- C oA, respectively?

There are two forms of the enzyme acyl-CoA dehydroge- nase (see Fig. l7-8a): long-chain acyl-CoA dehydrogenase (LCAD) and very-long-chain acyl-CoA dehydrogenase (VLCAD). Yu and coworkers measured the kinetic parameters of both enzymes. They used the CoA derivatives of three fatty acids: tetradecanoyl-CoA (C1a-CoA), c'i,s-L5-tetradecenoyl- CoA (cAsC,n-CoA), and trans-L5-tetradecenoyl-CoA (tAsOr4- CoA). The results are shown below. (See Chapter 6 for defini- tions of the kinetic parameters.)

(d) For LCAD, the K^ differs dramatically for the cis and trans substrates. Provide a plausible explanation for this observation in terms of the structures of the substrate mole- cules. (Hint: You may want to refer to Fig. I0-2.)

(e) The kinetic parameters of the two enzymes are rele- vant to the differential processing of these fatty acids only tf the LCAD or VLCAD reaction (or both) is the rate-limiting step in the pathway. What evidence is there to support this assumption?

(f) How do these different kinetic parameters explain the different levels of the CoA derivatives found after incubation of rat liver mitochondria with stearoyl-CoA, oleoyl-CoA, and elaidoyl-CoA (shown in the three-panel figure)?

Yu and coworkers measured the substrate specificity of rat liver mitochondrial thioesterase, which hydrolyzes acyl- CoA to CoA and free fatty acid (see Chapter 21). This enzyme was approximately twice as active with C1a-CoA thioesters as with C 1s-CoA thioesters.

(S) Other research has suggested that free fatty acids can paSS through membranes. In their experiments, Yu and colleagues found trans-L5-tetradecenoic acid outside mito- chondria (i.e., in the medium) that had been incubated with elaidoyl-CoA. Describe the pathway that led to this extramito- chondrial trans-L5-tetradecenoic acid. Be sure to indicate where in the cell the various transformations take place, as well as the enzymes that catalyze the transformations.

(h) It is often said in the popular press that "trans fats are not broken down by your cells and instead accumulate in your body." In what sense is this statement correct and in what sense is it an oversimplification?

1. Which of the following is the correct sequence of events (from start to finish) in cellular fatty acid oxidation?

A. Fatty acid activationÃ carnitine shuttleÃ beta-oxidation

B. Beta-oxidationÃ carnitine shuttleÃ Fatty acid activation

C. Fatty acid activationÃ carnitine shuttleÃ beta-oxidation

D. Carnitine shuttleÃ Fatty acid activationÃ beta-oxidation

2. What reaction is catalyzed by lipoprotein lipase, or lipase?

A. Hydrolysis of TAGs into fatty acids and glycerol

B. Hydrolysis of TAGs into amino acids and glycerol

C. Hydrolysis of cholesterol in to fatty acid and water

D. Hydrolysis of cholesterol into acetyl-CoA

3. How do fatty acids of different carbon lengths cross into the mitochondrial matrix for oxidation?

A. Small FAs of 10 carbons or fewer can freely diffuse through the membrane

B. Large FAs are cleaved into two smaller units that are actively transported across the membrane

C. A membrane-bound transferase catalyzes the conversion of long-chain FAs and FA-carnitine esters, which are transported across the membrane via a specific carrier

D. The breakdown of large FAs starts outside the matrix, allowing for the smaller particles to pass easily through the membrane

4. How can any RNA nucleotide be easily distinguished from a DNA nucleotide?

A. RNA nucleotides have a unique phosphodiester bond linkage

B. RNA nucleotides have uracil nitrogenous bases

C. RNA nucleotides have an -OH on the 2â carbon of the ribose

D. RNA nucleotides cannot be easily distinguished from DNA nucleotides

5. Which of the following statement is true concerning the sequence pTACGTAACGTA?

A. This is an RNA sequence

B. In order to have a more rigid structure in a double-stranded molecule, the sequence given would need more adenosine

C. If the complementary strand were present, the number of purines would be equal to the number of pyrimidines

D. The amount of purines is equal to the amount to pyrimidines

6. Complementary base pairing is considered which level of structure?

A. Secondary

B. Tertiary

C. Quaternary

D. Primary

7. Which of the following is/are required for the polymerization reaction catalyzed by DNA polymerase III?

I. RNA primer

II. DNA primer

III. RNA template

IV. DNA template

V. NTPs

VI. dNTPs

VII. Magnesium

VIII. Calcium

A. II, IV, V, and VII

B. II, IV, VI, and VII

C. I, IV, V, and VIII

D. I, IV, VI, and VII

8. DNA polymerase I, from E. coli, has three different catalytic sites. Which of the following is NOT one of them?

A. RNA-dependent RNA polymerase

B. RNA-dependent DNA polymerase

C. DNA-dependent RNA polymerase

D. DNA-dependent DNA polymerase

9. Eukaryotes solve the problem of replicating the ends of their linear chromosomes by:

A. Using a protein as primer

B. Enzyme activity that uses an RNA template and reverse transcription in a series of repeat cycles

C. All of the listed solution

D. Terminal redundancy whereby each end of the chromosome is duplicated allowing recombination

BIOC 3021 Study Guide - Midterm Guide: Ketone, Fatty Acid Synthase, Acetoacetic Acid

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