1.Enzymes-proteins that catalyze chemical and biochemical reactions with living cells and outside. Proteins are responsible for all metabolic reactions in the living cell. Well known and very interesting examples are DNA and RNA.
2. Hormones–proteins are responsible for the regulation of many processes in organisms. Hormones are quite small and can be classified as peptides.
3. Transport proteins–these proteins are transporting or store some other chemical compounds and ions (the smallest particles) in the body. For example some of the hemoglobin and myoglobin etc.
4. Immunoglobulin or Antibodies– proteins are released in the body in response to some infection, as a natural defense mechanism of the body, they are called antibodies (to fight for the bodies foreign for the body). Sometimes antibodies can act as enzymes.
5. Structural protein- these proteins are main structures of a biochemical compound like various cells and tissues of the body.
6. Motor protein– these proteins can convert chemical energy (energy of chemicals) into mechanical energy (energy brought by action). Actin and myosin muscles are responsible for muscular motion.
7. Receptors- these proteins are responsible for signal detection and translation into another type of signal.
8. Signaling proteins- this group of proteins is involved in the signaling translation process. Usually, they significantly change conformation in the presence of some signaling molecules. These can act as enzymes.
9. Storage proteins– these proteins contain energy, these proteins contain energy, which can be released during metabolism processes in the organism. Egg ovalbumin and milk casein are such proteins.
Functions of protein in the body
1. Required for the building and repair of worn and torn tissues of the body.
2. Most of the important enzymes which are extremely important in digestion is basically protein; hormones which regulate the whole functioning of the body, growth, development, and reproduction in all animals are also protein. The molecules (called immune molecules) responsible for fighting with foreign harmful invaders of the body generally known as viruses and bacteria are also protein.
3. Protein helps to transport other nutrients around the body by binding to them when and where they are required or needed.
4. Certain proteins serve a major structural role in tissue such as muscle and skin and even provide the matrix for bone and the teeth.
5. Essential body processes such as water balancing which is very important to maintain proper blood pressure in the body and lubrication of the eyes are done by proteins.
6. Proteins also bring muscle contraction which is very important in all types of body movements through the special tissues called actin and myosin.
Protein is a source of energy for the body as well; 1 gram of protein in the diet provides 4 Kcal of energy to the body.
Complete protein and incomplete proteins
Proteins are made up of chains of amino acids, so the dietary proteins. Some amino acids are synthesized in the body while some could not be. Those amino acids which could not be synthesized in the body are called an essential amino acid, as they have to get through diet for normal health. All those food items which contain most of the amino acids are called ‘High Biological Value’ proteins, all non vegetarian food, milk, and milk products and in vegetarian food soy products are considered as ‘complete proteins’. In a vegetarian diet the rich sources of proteins like pulses and legumes lack most of the amino acids and are considered not so good quality protein (except soy products) and are called ‘Low Biological Value’ protein, but non- vegetarian food give so much of health hazards like coronary artery disease, high cholesterol, colon cancer, hyperlipidemia, hypertension, and diabetes, etc. that in spite of giving good quality the protein they cannot be advised at all for the consumption. In vegetarian any combination of cereal and pulses give a ‘complete protein’ the very common examples are daal chawal, rajma chaawal, beans and chapatti, pulses and chapatti etc., in fact normally we consume protein in this combination only. So, one should not bother about the ‘quality’ of protein, even if one is having strictly vegetarian diet.