Problem 1 - Biochemistry: Concepts and Connections

Question

Calculate the ATP yield from oxidation of palmitic acid, taking into account the energy needed to activate the fatty acid and transport it into mitochondria. Do the same for stearic acid, linoleic acid, and oleic acid.

Step-by-Step Solution

Answer

Palmitic: 106 ATP, Stearic: 120 ATP, Oleic: 120 ATP, Linoleic: 120 ATP.

Step 1: Activation and Transport into Mitochondria

First, calculate the ATP cost associated with activating the fatty acid and transporting it into mitochondria. Fatty acids need to be transformed into acyl-CoA and then transported via carnitine shuttle. This process costs 2 ATP for all fatty acids regardless of the type. Thus, the cost will be 2 ATP for palmitic acid, stearic acid, linoleic acid, and oleic acid.

Step 2: Determine Number of Carbon Atoms

Identify the number of carbon atoms in each fatty acid: palmitic acid has 16 carbons, stearic acid has 18 carbons, oleic acid has 18 carbons, and linoleic acid has 18 carbons.

Step 3: Calculate Beta-Oxidation Cycles

Determine the number of beta-oxidation cycles needed for each fatty acid. This is calculated as \((n/2) - 1\), where \(n\) is the number of carbon atoms. Hence, palmitic acid requires 7 cycles, and stearic, oleic, and linoleic acids each require 8 cycles.

Step 4: ATP Yield from Beta-Oxidation

Each cycle of beta-oxidation produces 1 FADH\(_2\) and 1 NADH. Multiply the number of cycles by ATP yield per FADH\(_2\) (1.5 ATP) and NADH (2.5 ATP). Thus, for each cycle, 4 ATP are produced: - Palmitic acid: 7 cycles x 4 ATP = 28 ATP- Stearic acid: 8 cycles x 4 ATP = 32 ATP- Oleic acid: 8 cycles x 4 ATP = 32 ATP- Linoleic acid: 8 cycles x 4 ATP = 32 ATP

Step 5: ATP Yield from Acetyl-CoA

Each complete beta-oxidation results in acetyl-CoA, which enters the Krebs cycle. Multiply the number of two-carbon units (acetyl-CoA) by the ATP yielded per cycle (10 ATP per acetyl-CoA from 1 GTP, 1 FADH\(_2\), and 3 NADH):- Palmitic acid (8 acetyl-CoA): 8 x 10 = 80 ATP- Stearic acid (9 acetyl-CoA): 9 x 10 = 90 ATP- Oleic acid (9 acetyl-CoA): 9 x 10 = 90 ATP- Linoleic acid (9 acetyl-CoA): 9 x 10 = 90 ATP

Step 6: Calculate Total ATP Yield

Now add the ATP yield from beta-oxidation and the Krebs cycle, then subtract the activation cost: - Palmitic acid: (28 + 80) - 2 = 106 ATP - Stearic acid: (32 + 90) - 2 = 120 ATP - Oleic acid: (32 + 90) - 2 = 120 ATP - Linoleic acid: (32 + 90) - 2 = 120 ATP

Key Concepts

Beta-Oxidation

Beta-oxidation is a crucial step in the metabolic breakdown of fatty acids. This process takes place in the mitochondria, where long-chain fatty acids are oxidized to generate acetyl-CoA. During beta-oxidation, the fatty acid chain is broken down in repeated cycles. Each cycle shortens the fatty acid by two carbon atoms and produces key molecules: one FADHeume1_mut">_2eume0_end"> and one NADH. - The number of cycles required for beta-oxidation is determined by the formula \( n/2 - 1 \), where \( n \) represents the number of carbons in the fatty acid.- For palmitic acid with 16 carbons, 7 cycles are needed.- Stearic, oleic, and linoleic acids each have 18 carbons, requiring 8 cycles.Each cycle contributes to the overall ATP yield, making beta-oxidation an energy-efficient part of fatty acid metabolism. This process not only provides ATP but also generates acetyl-CoA for further energy production in the Krebs cycle.

Acetyl-CoA

Acetyl-CoA is a significant molecule in both fatty acid metabolism and the Krebs cycle. During beta-oxidation, each cycle releases acetyl-CoA. This molecule acts as a central hub for energy production because it enters the Krebs cycle, also known as the citric acid cycle. - For palmitic acid, each beta-oxidation yields 8 acetyl-CoA molecules. - Stearic acid, oleic acid, and linoleic acid, each derive 9 acetyl-CoA molecules from their cycles. Acetyl-CoA is transformed further in the Krebs cycle, where it generates additional ATP, NADH, and FADH eume1_mut">_2 eume0_end">, contributing significantly to the cell's energy requirements. The ability of acetyl-CoA to funnel into various metabolic pathways underscores its importance in cellular respiration.

Fatty Acid Metabolism

Fatty acid metabolism is vital for providing cells with energy. This process involves several stages, starting with the activation of fatty acids. Initially, fatty acids are converted into acyl-CoA through the expenditure of 2 ATP molecules. Then, the acyl-CoA is transported into the mitochondria via the carnitine shuttle system. Once inside the mitochondria, the fatty acids undergo beta-oxidation, leading to the production of acetyl-CoA, NADH, and FADH eume1_mut">_2 eume0_end">. These products are then used to generate ATP through the Krebs cycle and oxidative phosphorylation. - This pathway is pivotal for metabolizing fatty acids like palmitic, stearic, oleic, and linoleic acids. - Each type of fatty acid yields varying ATP amounts due to differences in carbon chain length. Overall, fatty acid metabolism is an efficient mechanism for energy production, especially during prolonged exercise or fasting when carbohydrates are less available.

Krebs Cycle

The Krebs cycle, or citric acid cycle, is integral to cellular energy production. Once acetyl-CoA is formed from beta-oxidation, it enters the Krebs cycle where major energy carriers, NADH and FADH eume1_mut">_2 eume0_end">, are produced. - Each acetyl-CoA that enters the cycle generates 3 NADH, 1 FADH eume1_mut">_2 eume0_end">, and 1 GTP, which is equivalent to ATP. - This cycle occurs in the mitochondria matrix, linking glycolysis and beta-oxidation to the electron transport chain. The Krebs cycle's ability to convert fuel molecules into usable energy is crucial for the overall ATP yield. With acetyl-CoA derived from fatty acids like palmitic and stearic acids, the Krebs cycle enables the conversion of stored energy from fat into ATP, powering cells efficiently. This systematic conversion makes the cycle vital for organisms requiring energy for sustained activity.