Question

Consider the complete oxidation of oleic acid, \(\mathrm{CH}_{3}-\left(\mathrm{CH}_{2}\right)_{7}-\mathrm{CH}=\mathrm{CH}-\left(\mathrm{CH}_{2}\right)_{7}-\mathrm{COOH}\), which is an 18-carbon monounsaturated fatty acid. a. How many acetyl CoA units are produced? b. How many cycles of \(\beta\) oxidation are needed? c. How many ATPs are generated from the oxidation of oleic acid?

Short answer

a) 9 acetyl CoA units; b) 8 \beta-oxidation cycles; c) 122 ATP

Step-by-step solution

Identify the total number of carbons in oleic acid

Oleic acid has 18 carbon atoms. This can be verified from its molecular structure.

Determine the number of acetyl CoA units

Each acetyl CoA unit contains 2 carbon atoms. Therefore, the number of acetyl CoA units produced from the complete oxidation of oleic acid is calculated as follows: \(\frac{18 \text{ carbons}}{2} = 9 \text{ acetyl CoA units}\).

Calculate the number of \beta-oxidation cycles

\beta-oxidation involves the removal of a 2-carbon fragment (in the form of acetyl CoA) in each cycle. Since 9 acetyl CoA units are produced, the number of cycles required is given by:\(9 \text{ acetyl CoA units} - 1 = 8 \text{ cycles}\).

Determine ATP generated from acetyl CoA

Each acetyl CoA yields 10 ATP through the citric acid cycle (TCA cycle) and oxidative phosphorylation. Therefore, the total ATP from 9 acetyl CoA units is:\(9 \text{ acetyl CoA units} \times 10 \text{ ATP/acyl CoA} = 90 \text{ ATP}\).

Calculate ATP from \beta-oxidation

Each \beta-oxidation cycle produces 1 FADH\(_2\) (1.5 ATP each) and 1 NADH (2.5 ATP each). Thus, the ATP from 8 such cycles is:\(8 \text{ cycles} \times (1.5 \text{ ATP (FADH}_{2}) + 2.5 \text{ ATP (NADH)}) = 8 \times 4 \text{ ATP} = 32 \text{ ATP}\).

Calculate the total ATP generated

Sum the ATP produced from acetyl CoA units and from \beta-oxidation cycles:\(90 \text{ ATP} + 32 \text{ ATP} = 122 \text{ ATP}\).

Key concepts

beta-oxidation

Beta-oxidation is a crucial metabolic process involving the breakdown of fatty acids to generate energy. It occurs in the mitochondria of cells. Here's how it works in simple terms: Each cycle of beta-oxidation removes a two-carbon unit from a fatty acid, converting it into acetyl CoA. This process continues until the entire fatty acid is broken down. For example, in the oxidation of an 18-carbon fatty acid like oleic acid, 8 cycles of beta-oxidation are needed, producing 9 acetyl CoA molecules. Understanding beta-oxidation is important for grasping how our bodies convert fat into usable energy. During beta-oxidation, important molecules such as FADH2 and NADH are also produced. These molecules play a significant role in transferring electrons to the electron transport chain, leading to ATP production.

acetyl CoA

Acetyl CoA is a critical molecule in metabolism. It acts as the fuel for the citric acid cycle (TCA cycle), which is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins. Each acetyl CoA consists of a two-carbon acetyl group linked to coenzyme A. In the complete oxidation of oleic acid, an 18-carbon monounsaturated fatty acid, 9 acetyl CoA molecules are produced, which then enter the citric acid cycle. During the citric acid cycle, each acetyl CoA undergoes a series of reactions, releasing energy that powers the production of ATP, the cell's main energy currency. The generation of acetyl CoA from fatty acids showcases the remarkable energy potential stored in fats. Without acetyl CoA, the efficient production of ATP through the citric acid cycle and oxidative phosphorylation would not be possible.

ATP production

ATP (adenosine triphosphate) is the primary energy carrier in cells, providing the energy required for various cellular processes. The complete oxidation of fatty acids, such as oleic acid, plays a key role in ATP production. From the earlier example of oleic acid, the total ATP generated is divided into two sources: acetyl CoA and beta-oxidation cycles. Each of the 9 acetyl CoA units enters the citric acid cycle, yielding 10 ATP per unit, totaling 90 ATP. Additionally, each of the 8 beta-oxidation cycles produces FADH2 and NADH, which yield a combined 4 ATP per cycle, adding up to 32 ATP. Summing these values, the complete oxidation of oleic acid generates 122 ATP overall. This showcases not just the efficiency of fatty acid oxidation in energy production, but also why fats are a dense and valuable energy source.