Look back at the reactions of the citric acid cycle (Figure 21.8) and identify the three reactions in that cycle that are similar to the first three reactions of the β oxidation of a fatty acid.
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Verified step by step guidance

1. Step 1: Recall the key reactions in the citric acid cycle (Krebs cycle). These include oxidation-reduction reactions, hydration reactions, and substrate-level phosphorylation. Focus on the reactions that involve the transformation of citrate to isocitrate, isocitrate to α-ketoglutarate, and α-ketoglutarate to succinyl-CoA.
2. Step 2: Review the first three reactions of β-oxidation of a fatty acid. These include: (1) oxidation of the fatty acyl-CoA to form a trans double bond (using FAD as a coenzyme), (2) hydration of the double bond to form a hydroxyl group, and (3) oxidation of the hydroxyl group to form a keto group (using NAD+ as a coenzyme).
3. Step 3: Compare the first reaction of β-oxidation (oxidation using FAD) to the citric acid cycle reaction where succinate is oxidized to fumarate using FAD. Both involve the formation of a double bond and the use of FAD as an electron carrier.
4. Step 4: Compare the second reaction of β-oxidation (hydration of the double bond) to the citric acid cycle reaction where fumarate is hydrated to malate. Both involve the addition of water across a double bond.
5. Step 5: Compare the third reaction of β-oxidation (oxidation of the hydroxyl group using NAD+) to the citric acid cycle reaction where malate is oxidized to oxaloacetate using NAD+. Both involve the oxidation of a hydroxyl group to a keto group and the use of NAD+ as an electron carrier.

Key Concepts

Citric Acid Cycle

The citric acid cycle, also known as the Krebs cycle, is a series of enzymatic reactions that occur in the mitochondria, where acetyl-CoA is oxidized to produce energy in the form of ATP, NADH, and FADH2. It plays a crucial role in cellular respiration, linking carbohydrate, fat, and protein metabolism.

Beta-Oxidation

Beta-oxidation is the metabolic process by which fatty acids are broken down in the mitochondria to generate acetyl-CoA, which can then enter the citric acid cycle. This process involves a series of reactions that sequentially remove two-carbon units from the fatty acid chain, producing NADH and FADH2 as energy carriers.

Enzymatic Reactions

Enzymatic reactions are biochemical processes facilitated by enzymes, which are proteins that speed up chemical reactions without being consumed. In both the citric acid cycle and beta-oxidation, specific enzymes catalyze each step, ensuring the efficient conversion of substrates into products, and allowing for the regulation of metabolic pathways.