Chapter 23, Problem 42A

Interpretation Introduction

Interpretation:

The name of two polar and two non-polar amino acids should be determined.

Concept introduction:

Proteins are polymeric biomolecules which are formed by the polymerisation of amino acids. Amino acids are the organic molecules with $–{\text{NH}}_{\text{2}}$ and −COOH functional groups bonded on same carbon atom of the molecule.

They polymerise by peptide linkage to form dipeptide, oligopeptide and polypeptide molecules. Each peptide bond formation is a condensation reaction that occurs with the elimination of water molecule.

Answer to Problem 42A

Polar amino acids: Serine and Cysteine

Non-Polar amino acids: Glycine, Valine

Explanation of Solution

Polar amino acid is directed towards the outside of the protein because of the hydrophilic properties of side chain whereas the nonpolar amino acid is directed towards the inside of protein (R group repelled by water) because of the hydrophobic nature.

Nonpolar amino acids are: Glycine, Valine

The structure of glycine:

Glycine is nonpolar as it is neutral species; also nonpolar hydrogen is linked as shown below:

The structure of Valine:

Valine is nonpolar as it is neutral species; also nonpolar group is linked as shown below:

Polar amino acids are: Serine and Cysteine

The structure of Serine is:

Serine is polar amino acid as it consists of polar R group:

The structure of cysteine is:

Serine is polar amino acid as it consists of polar R group: