Question

Which of the following biomolecules is common to respiration-mediated breakdown of fats, carbohydrates and proteins ?

• A. Glucose-6-phosphate
• B. Fructose 1, 6-bisphosphate
• C. Pyruvic acid
• D. Acetyl CoA

Answer 1

The Correct Option is D

Metabolism of Carbohydrates, Fats, and Proteins 

Carbohydrates, fats, and proteins are the primary sources of energy for the body. They are metabolized and processed in different ways before they enter the common energy production pathways. Below is a detailed explanation of how each macronutrient is broken down and utilized in cellular respiration:

Carbohydrate Metabolism:

• Carbohydrates are usually first converted into glucose before they are used for respiration.
• Glucose then undergoes glycolysis to form pyruvate, which is further processed in the Krebs cycle or converted into acetyl-CoA.

Fat Metabolism:

• Fats are first broken down into glycerol and fatty acids.
• Fatty acids are further degraded into acetyl-CoA, which enters the Krebs cycle.
• Glycerol is converted into 3-phosphoglyceraldehyde (PGAL) and then enters the glycolysis pathway.

Protein Metabolism:

• Proteins are broken down into individual amino acids by proteases.
• Amino acids undergo deamination, and depending on their structure, they enter the energy pathways either as pyruvate, acetyl-CoA, or directly in the Krebs cycle.

Common Metabolite: Acetyl-CoA

The common metabolite that enters the Krebs cycle for energy production is acetyl-CoA. Regardless of whether the energy source is carbohydrates, fats, or proteins, the breakdown of these molecules converges at the production of acetyl-CoA, which then enters the Krebs cycle to generate ATP.

Summary:

• Carbohydrates: Converted to glucose, then to pyruvate, and enters the Krebs cycle as acetyl-CoA.
• Fats: Broken down into glycerol and fatty acids; fatty acids are converted to acetyl-CoA, and glycerol enters as PGAL.
• Proteins: Broken down into amino acids; deaminated and converted to pyruvate, acetyl-CoA, or directly into the Krebs cycle.

The flowchart of these processes illustrates the interrelationships between carbohydrates, fats, and proteins, all converging on the production of acetyl-CoA, which is the common metabolite for further energy production in the body.