Question

What is the maximum number of molecules of ATP that can be generated by a bacterium after the complete aerobic oxidation of a fat molecule containing three 12-carbon chains? (Assume that all the available energy released during catabolism goes to ATP production.)

Short answer

The maximum number of ATP molecules that can be produced by a bacterium following the complete aerobic oxidation of a fat molecule containing three 12-carbon chains is 189.

Step-by-step solution

Understanding Beta Oxidation

Each 12-carbon chain will go through a process called Beta oxidation which is the process by which fatty acid molecules are broken down in the cytosol in prokaryotes and in the mitochondria in eukaryotes to generate acetyl-CoA. Beta oxidation breaks down the fatty acid molecule two carbons at a time, generating one acetyl-CoA each time. So, a 12-carbon chain will produce 6 acetyl-CoA molecules.

The Krebs Cycle or Citric Acid Cycle

Next, each Acetyl-CoA produced goes through the Krebs or Citric Acid Cycle where a total of 1 ATP, 3 NADH and 1 FADH(\_2) are generated for each acetyl-CoA molecule processed. Therefore, from one 12-carbon chain processed, there are \(6 \times 1 = 6\) ATPs, \(6 \times 3 = 18\) NADH molecules, and \(6 \times 1 = 6\) FADH(\_2)molecules produced through the Krebs Cycle.

The Electron Transport Chain

The Electron Transport Chain (ETC), located in the mitochondria uses the NADH and FADH(\_2) produced in the Krebs Cycle to generate ATP. Each NADH molecule contributes enough energy to the ETC to produce about 2.5 ATP molecules and each FADH(\_2) molecule contributes enough to produce about 1.5 ATP molecules. This adds up to \((18 \times 2.5) + (6 \times 1.5) = 57\) ATP molecules.

Calculate Total ATP for All Three Chains

Since the fat molecule has three 12-carbon chains, multiply the ATP obtained from one chain by three: \(3 \times (6 [ATP from Krebs Cycle] + 57 [ATP from ETC]) = 189\) ATP molecules

Key concepts

Beta Oxidation

Beta oxidation is the first step in the aerobic oxidation of fatty acids, where fatty acid molecules are broken down to generate energy. This process happens differently in prokaryotes and eukaryotes. In prokaryotes, it occurs in the cytosol, while in eukaryotes, it takes place in the mitochondria.

• Fatty acids are broken down two carbons at a time.
• Each break produces an acetyl-CoA molecule.
• This cycle continues until the entire fatty acid chain is converted into acetyl-CoA.

In the original exercise, a 12-carbon chain undergoes beta oxidation and generates 6 acetyl-CoA molecules. Understanding this concept is crucial, as acetyl-CoA is a primary input into the next phase: the Krebs cycle.

Krebs Cycle

Once acetyl-CoA is generated, it enters the Krebs Cycle, also known as the Citric Acid Cycle. This cycle is essential for energy production because it generates high-energy electron carriers used later.

• For each acetyl-CoA, the cycle produces 1 ATP, 3 NADH, and 1 FADH e_2.
• The cycle also regenerates the initial molecule, ready to process more acetyl-CoA.
• Overall, the cycle generates energy-rich carriers NADH and FADH e_2.

In our exercise, a single 12-carbon chain yields a total of 6 ATP, 18 NADH, and 6 FADH e_2 from the Krebs Cycle. The NADH and FADH e_2 are vital for the next stage, the Electron Transport Chain.

Electron Transport Chain

The Electron Transport Chain (ETC) is where most ATP is generated during the aerobic respiration of fatty acids. Located in the mitochondria, the ETC uses the electrons provided by NADH and FADH\(_2\) to produce ATP.

• NADH contributes enough energy to create about 2.5 ATP molecules.
• FADH\(_2\) contributes enough energy for approximately 1.5 ATP molecules.
• Electrons pass through a series of proteins, driving the production of ATP through oxidative phosphorylation.

In the step-by-step solution, it is shown that a 12-carbon chain produces 57 ATP from the ETC, emphasizing the importance of NADH and FADH\(_2\) in maximizing ATP yield during cellular respiration.

ATP Production in Bacteria

ATP production in bacteria from aerobic oxidation of fatty acids entails a highly efficient energy conversion process.

• In the initial exercise, one fatty acid chain theoretically yields 63 ATPs, contributed from both the Krebs Cycle and Electron Transport Chain.
• For a fat molecule with three 12-carbon chains, the total potential ATP yield is 189, calculated as 3 times 63 ATP per chain.
• The efficiency of this process relies on the full oxidation of fatty acids and electrons transfer.

This high ATP production from aerobic fatty acid breakdown underscores bacteria's capability to extract maximum energy, essential for survival and growth, especially in resource-scarce environments.