Which of the following always contains an amino functional group?
A. Carbonic acid
B. Alcohol
C. Protein
D. Fatty acid
E. Carbohydrate
The correct answer and explanation is:
The correct answer is C. Protein.
Proteins are complex biomolecules composed of long chains of amino acids. Each amino acid contains at least one amino group (-NH₂) as part of its structure. The amino group is one of the fundamental functional groups in amino acids, and its presence is essential for the formation of proteins.
Explanation:
Proteins are made by linking amino acids through peptide bonds in a process known as protein synthesis. An amino acid consists of three parts: an amino group (-NH₂), a carboxyl group (-COOH), and a unique side chain (R group) that determines the specific properties of each amino acid. The amino group is basic in nature and is responsible for the “amino” portion of the name “amino acid.”
In a peptide bond formation, the amino group of one amino acid reacts with the carboxyl group of another amino acid, releasing a water molecule and forming a covalent bond. This bond links the amino acids together into polypeptides, which, when folded and modified, form functional proteins. Therefore, the presence of the amino functional group is intrinsic to the structure of proteins.
Now, let’s briefly review the other options:
- A. Carbonic acid: This molecule contains a carboxyl group (-COOH) but does not contain an amino group. It is a weak acid formed when carbon dioxide dissolves in water.
- B. Alcohol: Alcohols contain a hydroxyl group (-OH), not an amino group. The amino group is absent in alcohol molecules.
- D. Fatty acid: Fatty acids contain a carboxyl group (-COOH) but no amino group. These molecules are primarily involved in forming lipids.
- E. Carbohydrate: Carbohydrates are made up of sugar units (monosaccharides) and do not contain amino groups. They primarily contain hydroxyl groups (-OH) and carbonyl groups (C=O).
Thus, the only option that always contains an amino functional group is protein.