Proteins

Proteins are biomolecules that are essential for the survival of the living organisms.

Proteins are polypeptides. They are linear chains of amino acids linked by peptide bonds as shown in below figure.

Primary structure of a portion of a hypothetical protein. N and C refer to the two termini of every protein. Single letter codes and three letter abbreviations for amino acids are also indicated.

Each protein is a polymer of amino acids. As there are 20 types of amino acids (e.g., alanine, cysteine, proline, tryptophan, lysine, etc.). The simplest amino acid is glycine.

A protein is a heteropolymer and not a homopolymer.

A homopolymer has only one type of monomer repeating ‘n’ number of times. This information about the amino acid content is important as later in your nutrition lessons, you will learn that certain amino acids are essential for our health and they have to be supplied through our diet. Hence, dietary proteins are the source of essential amino acids. Therefore, amino acids can be essential or non-essential. The latter are those which our body can make, while we get essential amino acids from our diet/food.

Proteins carry out many functions in living organisms, some transport nutrients across the cell membrane, some fight infectious organisms, some are hormones, some are enzymes, etc.

Some Proteins and their Functions

Protein	Functions
Collagen	Intercellular ground substance
Trypsin	Enzyme
Insulin	Hormone
Antibody	Fights infectious agents
Receptor	Sensory reception (smell, taste, hormone, etc.)
GLUT-4	Enables glucose transport into cells

Collagen is the most abundant protein in the animal world and Ribulose Bisphosphate Carboxylase-Oxygenase (RuBisCO) is the most abundant protein in the whole of the biosphere.