Question

(a) What is an \(\alpha\) -amino acid? (b) How do amino acids react to form proteins? (c) Draw the bond that links amino acids together in proteins. What is this called?

Short answer

(a) An alpha-amino acid is a molecule with an amino group (-NH2), a carboxyl group (-COOH), a side chain (R) and a hydrogen atom attached to a central carbon atom (alpha carbon). They are the building blocks of proteins. (b) Amino acids react to form proteins via peptide bond formation, a condensation reaction between the amino group and carboxyl group of two different amino acids. This forms a polypeptide chain, which determines the structure and function of the protein. (c) A peptide bond links amino acids in proteins. It consists of a covalent bond between the nitrogen atom of one amino acid's amino group and the carbon atom of another amino acid's carboxyl group (-NH-CO-).

Step-by-step solution

(a) Definition of an alpha-amino acid

An alpha-amino acid is a molecule consisting of an amino group (-NH2), a carboxyl group (-COOH), a side chain (R), and a hydrogen atom, all attached to a central carbon atom, called the alpha carbon. There are 20 common alpha-amino acids that make up the proteins in living organisms, and they differ in the structure of their R group.

(b) Reaction of amino acids to form proteins

Amino acids react to form proteins through a process called peptide bond formation, which is a type of condensation reaction. When the amino group of one amino acid reacts with the carboxyl group of another amino acid, water is removed, and a peptide bond is formed between the two amino acids. As more amino acids join, a polypeptide chain is created. The sequence of amino acids in a polypeptide chain determines the structure and function of the resulting protein.

(c) Drawing the bond and its name

In a peptide bond, the nitrogen atom of one amino acid's amino group is covalently linked to the carbon atom of another amino acid's carboxyl group through a single bond. The resulting structure is written as -NH-CO-, and is referred to as a peptide bond. Here is a schematic representation of the peptide bond between two amino acids: \[NH_{2}-R_{1}-C_{\alpha}-COOH + H_{2}N-R_{2}-C_{\alpha}-COOH \rightarrow NH_{2}-R_{1}-C_{\alpha}-CONH-R_{2}-C_{\alpha}-COOH + H_{2}O\] This formation of a peptide bond links the amino acids together in a protein.