When two amino acids are joined via a peptide bond, what is the mass of the byproduct of the reaction?
The Correct Answer and Explanation is :
When two amino acids are joined via a peptide bond, the reaction results in the formation of a dipeptide and the release of a molecule of water (H₂O). The mass of the byproduct, which is water, is approximately 18 grams per mole (g/mol).
Explanation
A peptide bond is a covalent bond that links the amino group (-NH₂) of one amino acid to the carboxyl group (-COOH) of another, with the elimination of a water molecule. This process is known as dehydration synthesis or condensation reaction because it involves the removal of a water molecule as the amino acids combine.
Let’s consider the general structure of amino acids. Each amino acid has a central carbon atom (Cα), an amino group, a carboxyl group, a hydrogen atom, and a variable R group (side chain). When two amino acids react, the carboxyl group of one amino acid interacts with the amino group of another. During this interaction, the -OH from the carboxyl group and one -H from the amino group are removed, combining to form water (H₂O).
In terms of molecular weights, the average molecular weight of an amino acid varies but is typically around 110 g/mol. When two amino acids combine to form a dipeptide, the total mass would be approximately 220 g/mol (110 g/mol + 110 g/mol). However, because a water molecule (H₂O), which weighs about 18 g/mol, is released during the formation of the peptide bond, the mass of the resultant dipeptide is 220 g/mol – 18 g/mol = 202 g/mol.
In summary, the byproduct of the reaction when two amino acids are joined by a peptide bond is water, with a mass of approximately 18 g/mol. This reaction is fundamental in biochemistry as it forms the building blocks of proteins, which are crucial for various biological functions.