Which of the following statements is true?

• A. Proteins are a primary source of energy along with carbohydrates & fat.
• B. Proteins are not a primary energy source, but they can be stored in the body for later energy use.
• C. Deamination is the removal of a single nitrogen atom from a protein, & this nitrogen is excreted in urine.
• D. Deamination is the removal of the amine group from a protein, which is converted to urea & then excreted.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the role of proteins in energy metabolism. Proteins are not considered a primary energy source like carbohydrates and fats. Instead, they are primarily used for growth, repair, and maintenance of body tissues. When energy intake is insufficient, proteins can be broken down for energy, but this is not their primary function.
2. Step 2: Clarify the concept of protein storage. Proteins are not stored in the body for later energy use. Instead, excess protein is broken down, and the nitrogen-containing amine group is removed through a process called deamination.
3. Step 3: Define deamination. Deamination is the removal of the amine group (-NH2) from an amino acid. This process occurs in the liver and is a key step in the metabolism of amino acids when they are used for energy or converted into other compounds.
4. Step 4: Explain the fate of the removed amine group. The amine group is converted into ammonia (NH3), which is toxic to the body. The liver then converts ammonia into urea, a less toxic compound, which is excreted from the body through urine.
5. Step 5: Evaluate the statements provided. Based on the explanation above, the correct statement is: 'Deamination is the removal of the amine group from a protein, which is converted to urea and then excreted.' This accurately describes the process of deamination and the fate of the nitrogen removed from amino acids.