Biochemistry: Fatty Acid Synthesis

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Questions and Answers

Which enzyme is responsible for the elongation of palmitate in microsomes?

Fatty acid elongase (correct)

Acetyl-CoA carboxylase

Fatty acyl CoA desaturase

NADPH oxidase

What is the primary source of 2-carbon units during mitochondrial elongation of fatty acids?

Malonyl-CoA

Palmitate

Acetyl-CoA (correct)

NADPH

What type of fatty acids do mammals lack the ability to introduce double bonds at specific positions?

Resting state fatty acids

Unsaturated fatty acids between carbon 10 and methyl terminal (correct)

Fatty acids with fewer than 10 carbons

Saturated fatty acids

Which of the following fatty acids can be synthesized from linoleic acid?

Arachidonic acid Signup and view all the answers

Which compound is not metabolized and is primarily exhaled through the lungs?

Acetone Signup and view all the answers

What process refers to the formation of ketone bodies?

Ketogenesis Signup and view all the answers

Which enzyme system is involved in the formation of unsaturated fatty acids?

Fatty acyl CoA desaturase Signup and view all the answers

Which of the following statements about ketone bodies is true?

β-Hydroxybutyrate does not possess a keto group Signup and view all the answers

Which enzyme is responsible for the conversion of β-hydroxy butyrate to acetoacetate?

β-Hydroxy butyrate dehydrogenase Signup and view all the answers

What is the primary precursor for ketone body synthesis?

Acetyl CoA Signup and view all the answers

What is the fate of acetoacetate in the absence of enzymatic decarboxylation?

It is converted to acetone spontaneously. Signup and view all the answers

During which condition does the production of ketone bodies become most significant?

Starvation Signup and view all the answers

Which ketone body is predominantly used by the brain during prolonged starvation?

β-Hydroxybutyrate Signup and view all the answers

What reaction is catalyzed by thiolase in ketogenesis?

Condensation of two acetyl-CoA to acetoacetyl-CoA Signup and view all the answers

Which of the following tissues is unable to utilize ketone bodies?

Erythrocytes Signup and view all the answers

What is the max concentration of total ketone bodies in well-fed conditions?

0.2 mmol/L Signup and view all the answers

Study Notes

Synthesis of Long Chain Fatty Acids from Palmitate

Fatty acid elongase in the microsomal enzyme system elongates palmitate using 2-carbon fragments from malonyl-CoA and reducing equivalents from NADPH.
Mitochondrial elongation of fatty acids is less active, primarily elongating fatty acids with less than 16 carbons, mainly short and medium chain fatty acids, using acetyl-CoA.
Fatty acyl CoA desaturase system in microsomes forms unsaturated fatty acids, requiring flavin-dependent cytochrome b5 reductase, NADH, and molecular oxygen.
Oleic acid (from stearate) and palmitoleic acid (from palmitate) are synthesized as monounsaturated fatty acids.
Mammals cannot introduce double bonds between the 10th carbon and the methyl terminal (ω) end, making linoleic and linolenic acids essential dietary components.
Arachidonic acid can be synthesized from linoleic acid via desaturation and chain elongation, serving as a precursor for eicosanoids like prostaglandins and thromboxanes.

Metabolism of Ketone Bodies

Ketone bodies (acetoacetate, β-hydroxybutyrate, and acetone) are water-soluble energy sources, with acetone exhaled and not metabolized.
Ketogenesis occurs exclusively in the liver, within the mitochondrial matrix of hepatic cells, utilizing acetyl-CoA derived from fatty acid oxidation, pyruvate, or specific amino acids.
Ketogenesis involves the condensation of two acetyl-CoA molecules to form acetoacetyl-CoA, followed by condensation with another acetyl-CoA to create β-HMG-CoA, regulated by HMG-CoA synthase.
HMG-CoA is then cleaved into acetoacetate and acetyl-CoA by HMG-CoA lyase, while β-hydroxybutyrate is produced by reducing acetoacetate using β-hydroxybutyrate dehydrogenase.
Acetoacetate can spontaneously decarboxylate into acetone, with blood ketone body concentrations not exceeding 0.2 mmol/L in well-fed conditions.

Utilization of Ketone Bodies

Ketone bodies (acetoacetate and β-hydroxybutyrate) serve as significant energy sources for peripheral tissues, including skeletal muscle and cardiac muscle.
Tissues such as erythrocytes, lacking mitochondria, cannot utilize ketone bodies.
The production and utilization of ketone bodies increase significantly under conditions of low glucose availability, observed in starvation or diabetes mellitus.
During prolonged starvation, ketone bodies become a primary fuel source for the brain and other central nervous system regions.

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Description

This quiz covers the synthesis of long-chain fatty acids from palmitate, focusing on the mechanisms of microsomal and mitochondrial elongation. It explores the roles of enzymes like fatty acid elongase and the importance of malonyl-CoA and NADPH in the elongation process. Test your understanding of these biochemical pathways and their significance.