Protein is an important macronutrient essential for survival. They are constituent of calls and hence are present in all living bodies. 10-35% of calories should come from protein. Protein is found in meats, poultry, fish, meat substitutes, cheeses, milk etc. Proteins are large biological molecules composed of α-amino acids (Amino acid in which amino group is attached to α-carbon, which exist as zwitterions and are crystalline in nature). They contain carbon, hydrogen, oxygen, nitrogen and sometimes phosphorus and sulphur.
This video explains some simple tests of proteins.