Identify each of the following reactions a to e in the β oxidation of palmitic acid, a C₁₆ fatty acid, as
(1) activation
(2) first oxidation
(3) hydration
(4) second oxidation
(5) cleavage
a. Palmitoyl CoA and FAD form α, β-unsaturated palmitoyl CoA and FADH₂.

Verified step by step guidance

1. Step 1: Understand the context of β-oxidation. β-oxidation is the metabolic process by which fatty acids are broken down in the mitochondria to generate acetyl-CoA, NADH, and FADH₂. It involves a series of reactions that repeat in cycles, each removing a two-carbon unit from the fatty acid chain.
2. Step 2: Identify the specific reaction described in part (a). The reaction involves palmitoyl CoA reacting with FAD to form α, β-unsaturated palmitoyl CoA and FADH₂. This indicates that electrons are being transferred from the fatty acid to FAD, reducing it to FADH₂.
3. Step 3: Recognize the type of reaction. The transfer of electrons to FAD is characteristic of an oxidation reaction. Specifically, this is the first oxidation step in the β-oxidation cycle, where a double bond is introduced between the α and β carbons of the fatty acid.
4. Step 4: Match the reaction to the correct category. Based on the options provided, this reaction corresponds to (2) first oxidation, as it is the initial step where oxidation occurs in the β-oxidation process.
5. Step 5: Conclude that the reaction described in part (a) is categorized as the first oxidation step in the β-oxidation of palmitic acid.

Key Concepts

β-Oxidation

β-oxidation is a metabolic process that breaks down fatty acids into acetyl-CoA units, which can then enter the citric acid cycle for energy production. This process occurs in the mitochondria and involves a series of enzymatic reactions that sequentially remove two-carbon units from the fatty acid chain, starting from the carboxyl end.

Activation of Fatty Acids

Before β-oxidation can occur, fatty acids must be activated. This activation involves the conversion of a fatty acid into fatty acyl-CoA, catalyzed by the enzyme acyl-CoA synthetase. This reaction requires ATP and is essential for the fatty acid to be transported into the mitochondria for subsequent oxidation.

Enzymatic Reactions in β-Oxidation

The β-oxidation pathway consists of four main enzymatic reactions: oxidation, hydration, a second oxidation, and cleavage. Each step is catalyzed by specific enzymes, such as acyl-CoA dehydrogenase for the first oxidation, which introduces a double bond, and enoyl-CoA hydratase for hydration, which adds water to the double bond, facilitating the breakdown of fatty acids into acetyl-CoA.