Question

By which bond are amino acids joined together?

• A. Dipole-Dipole
• B. lonic
• C. Hydrogen
• D. Amide

Hint:

Peptide bond = Amide bond. Proteins are long chains of amino acids linked through peptide (amide) bonds.

Answer 1

The Correct Option is D

Concept: Proteins are polymers formed by the linkage of amino acids. Each amino acid contains: \[ -NH_2 \] and \[ -COOH \] functional groups. When two amino acids react, the carboxyl group of one amino acid combines with the amino group of another amino acid with the elimination of a water molecule. The resulting linkage is called a peptide bond, which is chemically an amide bond.

Step 1: Consider two amino acids. Let two amino acids be: \[ H_2N-CHR-COOH \] and \[ H_2N-CHR'-COOH \]

Step 2: Formation of peptide linkage. The reaction occurs as: \[ -COOH + -NH_2 \rightarrow -CONH- + H_2O \] Water is eliminated during the reaction.

Step 3: Identify the bond formed. The bond \[ -CONH- \] is an amide linkage. Therefore amino acids are connected through: \[ \boxed{\text{Amide Bond}} \] Hence option (4) is correct.