Question

What are the direct products of \(\beta\) oxidation of a fully saturated, straight-chain fatty acid of 11 carbons?

Short answer

5 acetyl-CoA, 1 propionyl-CoA, 5 NADH, and 5 FADH2.

Step-by-step solution

Understand \(\beta\) Oxidation

\(\beta\) oxidation is the metabolic process in which fatty acids are broken down in the mitochondria of cells to generate acetyl-CoA, NADH, and FADH2. Each cycle of \(\beta\) oxidation shortens the fatty acid by 2 carbons, releasing acetyl-CoA in each cycle.

Determine the Number of Cycles

A fully saturated, straight-chain fatty acid with 11 carbon atoms will undergo \(\frac{11-1}{2} = 5\) complete cycles of \(\beta\) oxidation. After these 5 cycles, one acetyl-CoA and a propionyl-CoA (3-carbon molecule) will be left over since 11 is an odd number.

Identify Products per Cycle

Each \(\beta\) oxidation cycle produces one molecule of acetyl-CoA, one molecule of NADH, and one molecule of FADH2. After 5 cycles, you will have 5 acetyl-CoA, 5 NADH, and 5 FADH2.

Account for the Remaining Atoms

After the 5 cycles, 3 carbon atoms remain from the original fatty acid. This 3-carbon chain forms a molecule of propionyl-CoA, which is not a typical acetyl-CoA but still represents the leftover product of \(\beta\) oxidation.

List the Final Products

The final direct products from the \(\beta\) oxidation of an 11-carbon saturated fatty acid are 5 acetyl-CoA, 1 propionyl-CoA, 5 NADH, and 5 FADH2.

Key concepts

Fatty Acid Metabolism

Fatty acid metabolism is a critical process in the body where fats are broken down to produce energy. This process primarily occurs in the mitochondria of cells, which are often referred to as the powerhouses of the cell. Fatty acids, composing the largest part of dietary fat, must first be converted into a form that the body can actually use by undergoing metabolic changes.
Here, one of the most important pathways is beta oxidation. This pathway helps to transform long-chain fatty acids into smaller molecules, specifically acetyl-CoA, that can easily enter into the citric acid cycle to produce energy efficiently.

• Beta oxidation involves repetitive cycles, each cycle shortening the fatty acid chain by two carbon atoms.
• This breakdown also generates crucial energy carriers in the form of NADH and FADH2.

Understanding this process is key to appreciating how our bodies harness energy from fat.

Acetyl-CoA

Acetyl-CoA stands as a pivotal metabolic molecule derived during the breakdown of fats, carbohydrates, and proteins. In the context of fatty acid metabolism, acetyl-CoA is a direct product of the beta oxidation of fatty acids. During each cycle of beta oxidation, acetyl-CoA is produced as the two-carbon segments are removed from the fatty acid chain.
Why does acetyl-CoA matter? Well, it serves as an entry molecule for the citric acid cycle, where it is further oxidized to produce carbon dioxide, reduced electron carriers, and ATP, the energy currency of cells. Therefore, acetyl-CoA links fatty acid metabolism to the cellular energy-producing mechanisms.

• In a typical beta oxidation sequence, each cycle liberates one acetyl-CoA until the fatty chain is fully processed.
• These are eventually converted into flavored energy packets like ATP, fueling numerous cellular processes.

It's a crucial hub in metabolic pathways, contributing to the body's overall energy balance.

NADH and FADH2

NADH and FADH2 are essential molecules produced during the beta oxidation cycle. These molecules act as energy-rich carriers, transporting electrons to the electron transport chain in mitochondria, where they are used to produce ATP.
Why are NADH and FADH2 so important during beta oxidation? As the fatty acids break down, these molecules capture high-energy electrons released from each breakdown step.

• For every cycle of beta oxidation, one molecule each of NADH and FADH2 is produced.
• They serve as temporary holders of energy that is later converted to ATP through oxidative phosphorylation.

This part of the metabolism efficiently turns raw energy from fat into a usable form, underscoring their role in energy production.

Odd-Chain Fatty Acids

Odd-chain fatty acids have an interesting twist in their metabolism compared to the more common even-chain fatty acids. When these types of fatty acids undergo beta oxidation, their degradation process results in a distinctive product: propionyl-CoA. In the case of the 11-carbon fatty acid, after typical beta oxidation cycles, a leftover 3-carbon molecule, propionyl-CoA, is produced.
This leftover differs from acetyl-CoA, which is the usual terminal product of beta oxidation in even-chain fatty acids. Here is what happens:

• The completed cycles produce acetyl-CoA, NADH, and FADH2 as usual.
• However, since the original chain is odd, a three-carbon fragment, propionyl-CoA, is left after the cycles conclude.

This molecule enters a unique metabolic route, where it is converted into succinyl-CoA, entering the citric acid cycle for further energy extraction. This distinction highlights the unique pathways required to handle and fully utilize different types of fatty acids.