Overview of Proteins

Proteins are biologically significant macromolecules which have vital roles in almost all biological processes.
They are made up of amino acids, which are the building blocks of proteins. There are 20 different types of amino acids that can be combined to make a protein.
The order of the amino acids in a protein is determined by the sequence of a gene.
Proteins have a complex structure and can be classified into four categories: primary, secondary, tertiary, and quaternary structure.

Primary structure of Proteins

The primary structure of a protein is the unique sequence of amino acids.
Each protein has its own unique sequence that determines its shape and function.
Individual amino acids are coupled together by peptide bonds in a dehydration synthesis reaction that also involves the removal of a water molecule.

The secondary structure refers to the local structures of the protein.
It is achieved by hydrogen bonds between the peptide linkages, leading to the formation of alpha-helices and beta-pleated sheets.
These structures provide stability and are necessary for the proper functioning of the protein.

The tertiary structure of a protein is the complete 3-dimensional structure of the protein.
It is stabilised by numerous interactions, including hydrophobic interactions, ionic bonds and disulphide bonds.
The tertiary structure determines the function of the protein, as it creates the specific active sites which is unique for each protein.

Some proteins have a quaternary structure, which is formed by the association of two or more polypeptide chains.
This is found in complex proteins, such as haemoglobin (with four polypeptide chains).
The polypeptide chains may function independently of each other or may be tightly integrated.

Proteins have a wide array of functions in the body, including as enzymes, antibodies, transport carriers, and structural components.
Enzymes are proteins which act as biological catalysts, increasing the rate of metabolic reactions.
Antibodies are proteins that aim to identify and neutralise foreign objects such as bacteria and viruses.
Proteins work as transport carriers by binding to specific molecules and carrying them to the appropriate place in the body.
Proteins also contribute to the structural components of the cell, contributing to its shape, rigidity, and organisation.