Chapter 17, Problem 1QC

How are proteins formed and how can we describe their structures?

Interpretation Introduction

Interpretation:

The formation of proteins and their structure are to be described.

Concept Introduction:

A protein unit is composed of a number of smaller individual units called amino acids. Amino acids possess both the amino and carboxylic acid groups. Amino acids are linked together through a peptide bond which leads to the formation of proteins.

Explanation of Solution

The amino acids perform many biological functions including protein synthesis, which is their primary function. Protein synthesis is a complex process controlled by DNA.

The carboxylic acid group of one amino acid reacts with the amino group of another, releasing a water molecule from these two amino acids results in the formation of a peptide bond. The resultant molecule is called a dipeptide. The dipeptide reacts with another amino acid, forming as tripeptide. If many amino acids are linked in a peptide chain, it is called polypeptide. A polypeptide with a molar mass more than $5000\text{g/mol}$ is called a protein.

There are four different levels of protein structure as follows:

Primary structure: This provides the sequence of amino acids in polypeptide chain. The end of the polypeptide chain which has free amine group is called amino terminus(N-terminus) whereas the other end with free carboxylic group is called carboxylic terminus(C-terminus).

Secondary structure: There are two types of secondary structure- the α-helix and the β-sheets. The hydrogen bond donors and acceptors in the peptide backbone of α-helix and β-sheets are saturated.

Tertiary structure: It is a compact three-dimensional structure of folded α-helix and β-sheets.

Quaternary structure: Two or more polypeptides in three-dimensional structure aggregate together to form a quaternary structure.

Conclusion

Proteins are formed from the combination of a number of amino acids. The structure of protein is described in four different ways on the basis of the arrangement of aminoacids and peptide chains.