Four organic molecules nucleic acids ( DNA and RNA), proteins, carbohydrates and fats make up all the living things on earth. Without these there will be no life.
Of these, proteins perform the most versatile functions. They are necessary for a growing child to build the body tissues, for a sick person to heal. The enzymes which digest our food are proteins, as are the antibodies that fight disease and Haemoglobin which carries oxygen.
There are more than 10,000 proteins in our body to help carry out all these functions. But, all of them are made of different combinations of 20 amino acids. There is evidence that every living being uses these same 20 amino acids to make their proteins, Our body digests the proteins from our food. The amino acids are absorbed and are then used to synthesise our body proteins.
Unlike fats and carbohydrates, the extra proteins we eat are not stored by our body for future use. So eating adequate proteins regularly is very important. As there are no stores, supplying extra proteins in the diet when body demand increases is very important. So extra protein must be provided for athletes, body builders, pregnant women, patients recovering from a surgery or illness.