Most fatty acids have an even number of carbons and, therefore, are completely metabolized to acetyl-CoA. A fatty acid with an odd number of carbonsis metabolized to acetyl-CoA and one equivalent of propionyl-CoA. The following two reactions convert propionyl-CoA into succinyl-CoA, a citric acidcycle intermediate, so it can be further metabolized. Each of the reactions requires a coenzyme. Identify the coenzyme for each step. From what vitaminsare the coenzymes derived? (Hint: see Chapter 23.) COO− COO−CH2CH2methylmalonyl-CoA succinyl-CoA CH3CH2 SCoA

Most fatty acids have an even number of carbons and, therefore, are completely metabolized to acetyl-CoA. A fatty acid with an odd number of carbonsis metabolized to acetyl-CoA and one equivalent of propionyl-CoA. The following two reactions convert propionyl-CoA into succinyl-CoA, a citric acidcycle intermediate, so it can be further metabolized. Each of the reactions requires a coenzyme. Identify the coenzyme for each step. From what vitaminsare the coenzymes derived? (Hint: see Chapter 23.) COO− COO−CH2CH2methylmalonyl-CoA succinyl-CoA CH3CH2 SCoA

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter23: Fatty Acid Catabolism

Section: Chapter Questions

Problem 21P: Using the ActiveModel for enoyl-CoA dehydratase, give an example of a case in which conserved...

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1) Humans do not undergo net synthesis of carbohydrate from acetyl- CoA, yet carbons of acetyl -CoA can be incorporated into glucose and amino acids. Show pathways as to how this can happen. 2) A molecule -X inhibits oxidation of stearoyl-CoA by isolated mitochondria but has no effect on palmitoyl-carnitine oxidation, explain.
Acetly CoA can quickly enter the citric acid cyle by joining with a C4 compound and forming citrate. Meanwhile, GTP (or ATP) is generated using inorganic phosphate while succinyl CoA is converted to succinate. What is the main reason both acetly CoA and succinyl CoA can perform such work? a. Acetyl CoA and succinyl CoA both contain coenzyme A, which is a high-energy compound. b. Acetyl CoA and succinyl CoA both form an unstable thioester bond with coenzyme A. c. Acetyl CoA and succinyl CoA both bind with inorganic phosphate which is used to generate ATP (or GTP). d. Acetyl CoA and succinyl CoA both transiently form a covalent bond with the enzymes that catalyze the next reaction, pyruvate dehydrogenase and succinyl-CoA synthetase, respectively. e. Acetyl CoA and succinyl CoA use the energy collected from the electron transport chain.
Several pathways exist in different organisms for the metabolism of propionyl-CoA. Most organisms utilizethe pathway that feeds into the citric acid cycle via succinyl-CoA. Another metabolic route used by Clostridium kluyveriis a "continuation of -oxidation" and consists of the following enzymatic reactions: (a) propionyl-CoA is converted toacryloyl-CoA; (b) formation of 3-hydroxypropionyl-CoA; (c) conversion to malonyl semialdehyde CoA; (d) productionof malonyl-CoA, which is then (e) decarboxylated to produce acetyl-CoA. Outline the above steps between propionylCoA and acetyl-CoA. Show structures for the metabolites and indicate appropriate cofactors (free or bound) that may beinvolved.
Several pathways exist in different organisms for the metabolism of propionyl-CoA. Most organisms utilizethe pathway that feeds into the citric acid cycle via succinyl-CoA. Another metabolic route used by Clostridium kluyveriis a "continuation of -oxidation" and consists of the following enzymatic reactions: (a) propionyl-CoA is converted toacryloyl-CoA; (b) formation of 3-hydroxypropionyl-CoA; (c) conversion to malonyl semialdehyde CoA; (d) productionof malonyl-CoA, which is then (e) decarboxylated to produce acetyl-CoA. Outline the above steps between propionylCoA and acetyl-CoA. Show structures for the metabolites and indicate appropriate cofactors (free or bound) that may beinvolved. b) Suggest a mechanism for enzyme reaction (e).
The products of pyrimidine base catabolism, β-alanine and β-aminoisobutyrate, can be further degraded to acetyl-CoA and succinyl-CoA, respectively. Can you suggest the types of reaction required to accomplish these transformations?
Fatty acid biosynthesis begins with the condensation of a two-carbon acetyl residue from acetyl-COA and oxaloacetate, while oxidation leads to the release of two carbon units, acetyl-CoA and fatty acyl-CoA. However, these two processes are not simple reversal. Compare and contrast these two pathways.
Peroxisomes have an alternative pathway for oxidizing polyunsaturated fatty acids. They contain a hydratase that converts D-3-hydroxyacyl CoA into trans Δ²- enoyl CoA. How can this enzyme be used to oxidize CoAs containing a cis double bond at an evennumbered carbon atom (e.g., the cis-Δ¹² double bond of linoleate)?
Under conditions where ketone bodies are being produced in the liver, how many ATPS can be produced from a molecule of palmitic acid if all resulting molecules of acetyl-CoA are converted into B-hydroxybutyrate?
Thiolase is homologous in structure to the condensing enzyme. On the basis of this observation, propose a mechanism for the cleavage of 3-ketoacyl CoA by CoA.
On these following choices, Malonyl CoA synthase, Malonyl CoA synthetase, Acetyl CoA carboxylase and Acetyl CoA decarboxylase, what is the correct answer in fatty acid synthesis?
(i) Consider a preparation that contains all the enzymes and cofactors necessary for fatty acid biosynthesis from acetyl-CoA and malonyl-CoA. If [2-H] acetyl-CoA labeled with deuterium, the heavy isotope of hydrogen and excess of unlabeled malonyl-CoA are added as substrates, where will you find these labeled deuterium atoms in a molecule of palmitate synthesized? Explain. S-COA (ii) Describe the steps involved in the synthesis of palmitic acid starting from acetyl-CoA and malonyl-CoA.
Coenzyme A (CoA-SH) plays an important role in the Pyruvate Dehydrogenase Complex reaction. Which is correct? Coenzyme A serves as an electron acceptor in this reaction. The hydrolysis of a CoA thioester has a positive AG", the hydrolysis is endergonic and unfavorable. Coenzyme A is derived from thiamine, a vitamin. Coenzyme A contains -SH group and can serve as an acyl group carrier.