Total Energy from Fatty Acids: Videos & Practice Problems

The total ATP yield from the complete oxidation of a fatty acid involves several key processes. Initially, fatty acid activation incurs a cost of 2 ATP. During one cycle of beta-oxidation, 1 FADH₂ and 1 NADH are produced, along with 1 Acetyl CoA. In the citric acid cycle, 1 Acetyl CoA generates 1 ATP, 1 FADH₂, and 3 NADH. The total ATP from oxidative phosphorylation is calculated as 12 ATP, considering the contributions from NADH and FADH₂. This highlights the efficiency of fatty acid metabolism in energy production.

Total Energy from Fatty Acids Concept 1

Understanding the total energy yield from the complete oxidation of fatty acids is crucial in biochemistry, particularly in the context of cellular respiration. The process involves two main stages: beta oxidation and the citric acid cycle (Krebs cycle), followed by oxidative phosphorylation.

Initially, the oxidation of a fatty acid requires activation, which incurs a cost of 2 ATP. During one cycle of beta oxidation, one molecule of fatty acid generates one Acetyl CoA, one FADH₂, and one NADH. The FADH₂ and NADH produced are essential for the subsequent oxidative phosphorylation process, where they contribute to ATP production.

In the Krebs cycle, each Acetyl CoA yields one ATP, three NADH, and one FADH₂. Since we are considering only one Acetyl CoA from the beta oxidation of a single fatty acid, the outputs are halved compared to glucose metabolism, which typically produces two Acetyl CoA.

For the oxidative phosphorylation phase, the NADH and FADH₂ generated in both beta oxidation and the Krebs cycle are utilized to produce ATP. Each NADH contributes approximately 2.5 ATP, while each FADH₂ contributes about 1.5 ATP. Therefore, from one cycle of beta oxidation and one round of the Krebs cycle, the total ATP yield can be calculated as follows:

From beta oxidation: 1 NADH (2.5 ATP) + 1 FADH₂ (1.5 ATP) = 4 ATP

From Krebs cycle: 1 ATP + 3 NADH (7.5 ATP) + 1 FADH₂ (1.5 ATP) = 10 ATP

Adding these together gives a total of 14 ATP from the oxidation processes. However, accounting for the initial 2 ATP cost for fatty acid activation, the net yield becomes:

Net ATP = 14 ATP - 2 ATP = 12 ATP

In summary, the complete oxidation of a fatty acid results in a net yield of 12 ATP, highlighting the efficiency of fatty acids as an energy source in metabolic pathways. This understanding is essential for grasping how energy is derived from different macronutrients in biological systems.

Total Energy from Fatty Acids Example 1

To calculate the total ATP yield from the complete beta oxidation of myristic acid, a 14-carbon fatty acid, we follow a systematic approach. First, we determine the number of cycles of beta oxidation, which is calculated using the formula:

Number of cycles = (Number of carbons / 2) - 1

For myristic acid, this results in:

Number of cycles = (14 / 2) - 1 = 6

Next, we calculate the total number of NADH and FADH₂ produced during beta oxidation. Each cycle produces one NADH and one FADH₂, so:

NADH = 6

FADH₂ = 6

Now, we need to find the total ATP, NADH, and FADH₂ produced during the Citric Acid Cycle. The number of Acetyl CoA molecules generated from beta oxidation is given by:

Number of Acetyl CoA = Number of carbons / 2 = 14 / 2 = 7

From these 7 Acetyl CoA molecules, we can calculate the ATP yield as follows:

ATP from Acetyl CoA = 7 ATP

NADH from Acetyl CoA = 7 x 3 = 21 NADH

FADH₂ from Acetyl CoA = 7 x 1 = 7 FADH₂

Next, we convert the total NADH and FADH₂ to ATP from oxidative phosphorylation. Each NADH yields 2.5 ATP, and each FADH₂ yields 1.5 ATP. We first sum the NADH and FADH₂ from both beta oxidation and the Citric Acid Cycle:

Total NADH = 21 (from Citric Acid Cycle) + 6 (from beta oxidation) = 27 NADH

Total FADH₂ = 7 (from Citric Acid Cycle) + 6 (from beta oxidation) = 13 FADH₂

Now, we calculate the ATP yield from these totals:

ATP from NADH = 27 x 2.5 = 67.5 ATP

ATP from FADH₂ = 13 x 1.5 = 19.5 ATP

Finally, we sum all the ATP produced and account for the initial investment of 2 ATP required for activation:

Total ATP = 67.5 ATP + 19.5 ATP - 2 ATP = 85 ATP

Thus, the total ATP yield from the complete beta oxidation of myristic acid is 85 ATP.

Rank the following molecules based on amount of energy stored in them in increasing order (per mol).
I. Sucrose                           II. Arachidic                         III. Glucose                         IV. Behenic (22:0)

• A. I, III, II, IV
• B. III, I, II, IV
• C. II, IV, III, I
• D. IV, II, I, III

Answer: (B)

Provide total moles of ATP produced by complete β-oxidation of 3.4 g of palmitic acid (256.43 g/mol).

• A. 1.4 ATP
• B. 31.2 ATP
• C. 106 ATP
• D. 1.43 ATP

Answer: (A)

Here’s what students ask on this topic:

How is the total ATP yield from fatty acid oxidation calculated?

The total ATP yield from fatty acid oxidation is calculated by considering several key steps. First, fatty acid activation costs 2 ATP. During one cycle of beta-oxidation, 1 FADH₂ and 1 NADH are produced, along with 1 Acetyl CoA. In the citric acid cycle, 1 Acetyl CoA generates 1 ATP, 1 FADH₂, and 3 NADH. The total ATP from oxidative phosphorylation is calculated by converting NADH and FADH₂ into ATP. Each NADH yields 2.5 ATP and each FADH₂ yields 1.5 ATP. Summing these contributions gives the total ATP yield.

What is the role of Acetyl CoA in the citric acid cycle during fatty acid oxidation?

Acetyl CoA plays a crucial role in the citric acid cycle during fatty acid oxidation. Each Acetyl CoA enters the citric acid cycle and generates 1 ATP, 1 FADH₂, and 3 NADH. These high-energy molecules are then used in oxidative phosphorylation to produce ATP. The citric acid cycle is essential for converting the energy stored in Acetyl CoA into a form that can be used by the cell, highlighting its importance in energy metabolism.

How many ATP molecules are produced from NADH and FADH₂ during oxidative phosphorylation?

During oxidative phosphorylation, each NADH molecule produces 2.5 ATP, and each FADH₂ molecule produces 1.5 ATP. For example, if you have 4 NADH molecules, they will produce 10 ATP (4 x 2.5). Similarly, if you have 2 FADH₂ molecules, they will produce 3 ATP (2 x 1.5). These conversions are crucial for understanding the total ATP yield from fatty acid oxidation.

What is the initial ATP cost for fatty acid activation?

The initial ATP cost for fatty acid activation is 2 ATP. This activation step is necessary to prepare the fatty acid for subsequent beta-oxidation. Although it incurs an energy cost, it is essential for the efficient breakdown and utilization of fatty acids in energy metabolism.

Why is fatty acid metabolism considered efficient in energy production?

Fatty acid metabolism is considered efficient in energy production because it generates a high yield of ATP. Each cycle of beta-oxidation produces 1 FADH₂ and 1 NADH, which are converted into ATP during oxidative phosphorylation. Additionally, the citric acid cycle generates further ATP, FADH₂, and NADH from Acetyl CoA. Despite the initial ATP cost for activation, the overall process yields a significant amount of ATP, making it a highly efficient energy source.