Protein: Introduction, categories, importance of protein

General introduction

Protein: Introduction, categories, importance of protein

This name of protein was given by Berzelius and Mulder in 1838–1839. Protein makes up about 14% of all living bodies and up to 50% of dead and dried bodies. Therefore, it is clear from this that the amount of proteins is the highest in human food. Vegetarian people get proteins from grains, milk, pulses, etc. They are highly condensed in pulses.

In addition to carbon, hydrogen, and oxygen, about 16% of nitrogen is in combination with proteins. Not only this, there are often Pieces of Gandhak, phosphorus, iodine iron, etc. In complete breakdown, the molecules of pure proteins are broken down into molecules of simple amino acids. Therefore, proteins are compounds of amino acids, that is, amino acids are their coordinating units or monomers.

About 300 types of amino acids are found in nature. Protoplasm also contains many types of amino acids, but out of these only 20 types of amino acids are monomers of proteins. 

Out of these 20 types of amino acids, 10 types of amino acids can also be obtained from food and can also be made in body cells. These are called nonessential amino acids. We get the remaining 10 types of amino acids only from food. Hence they are called essential amino acids.

The proteins in our diet which contain all the essential amino acids are called complete proteins. The food that contains such proteins is called complete food. On the contrary, the proteins which do not contain all the essential amino acids are called incomplete proteins and the food containing them is called incomplete food.
The proteins in food that contain all the amino acids required for the synthesis of structural proteins are called adequate proteins. Conversely, the proteins of food whose amino acids can only be used for energy production are called inadequate proteins.

  • Protein molecules are very large and often three-dimensional macromolecules or polymers. Any two to twenty types of amino acids can be its components.

  • If we estimate words made from different combinations of 26 letters of the English alphabet, So it becomes easily clear that the number and variety of proteins are the highest in organisms and the structure and function of organisms mainly contain the roles of these molecules.

  • A cell of our body can have 10,000 different types of protein molecules.

  • In our full body, an estimate of a variety of proteins is made from 50,000 to 1,00,000.

  • Scientists are now coming to the conclusion that the proteins of any two types of cells of the same organism, the proteins of any two animal species, and all the proteins of two members of a species are not the same. Not only this, but based on these, efforts are being made to know the origin of animals.

The following three major categories and many subcontracts of bio-proteins are-
  1. Simple or Pure Proteins
  2. Conjugated Proteins
  3. Derived proteins

1. Simple or Pure Proteins - They are made up of only amino acid units i.e. monomers. They have two major distinctions based on the structure and figure of molecules -
  • Globular Proteins
  • Fibrous Proteins

Globular Proteins 

These are soluble in dilute solutions of water, salt, acids, and alkalis, but in composition, these are proteins with complex molecules.

• They are diffusible in their solutions and form colloidal solutions. Their molecules do not contract, but remain round by being folded and coiled.

• They have special importance in metabolic reactions.

• All enzymes, many hormones (such as insulin, thyroxine, ACTH, etc.), antitoxins or antibodies that destroy harmful bacteria and substances, albumin and globulins of eggs and blood plasma, globin of hemoglobin, Myoglobin of muscles, histones of nucleoproteins, glutelins of cereals, prolamines of pulses, etc. are all globular proteins.

• The concentrated proteins present in pulses are prolamines only. They are a major source of proteins for vegetarian Indians.

Fibrous Proteins
  • These are insoluble, structural proteins in water that participate in the creation of animals.
  • Connective tissues, tendons, cartilages, collagen of bones, etc. elastin, and reticulin, keratin of skin, horns, nails, feathers, hair, etc., fibroin of silk, actin, and myosin of muscles, fibrin of blood clot, etc. are all fibrillar proteins. Their molecules are long, threadlike, and contractile.

2. Conjugated Proteins: These are compounds of simple proteins and some other substances. These other substances are often called prosthetic groups. Based on the chemical composition of these groups, there are the following subcategories of Conjugated proteins -

(a) Nucleoprotein 
  • On hydrolysis give amino acid and nucleic acid. 
  • Weakly acidic in nature. 
  • Soluble in water. 
  • Found in the nucleus. 
  • Other examples-ribosomes and viruses.

(b) Glycoproteins 
  • Prosthetic group polysaccharide. 
  • On hydrolysis produced amino acids and carbohydrates.
  • Soluble in alkalies solution. 
  • Acedic in nature.
  • Found in jellyfish, saliva, and cell membranes.

(c) Lipoproteins 
  • On hydrolysis produced lipids and proteins. 
  • Prosthetic group lecithin and cephalin. 
  • In soluble in water. 
  • Found in the nucleus, lamellae of chloroplast.

(d) Chromoproteins 
  • Prosthetic group pigment. 
  • based on pigment, it is divided into chloroproteins and haemoproteins. 
  • Found in hemoglobin, myoglobins, and carotenoid proteins.

(e) Metalloproteins 
  • Contains no special protein stances other than metallic stances. 
  • Example: Ferridoxine and ferritin and certain metal-activated peptidase enzymes.

(f) Lecithoprotein 
  • Contains phosphorylated fats, 
  • Prosthetic group lecithin.

(g) Phosphoprotein 
  • Phosphoric acid is a prosthetic group. 
  • Insoluble in water. 
  • Soluble in alkalies. 
  • Example: casein in milk, vitelline in egg.

3. Derived proteinsThese proteins are not present in nature as such. They are obtained as a result of hydrolysis of natural proteins. During this process, the gradual stages are as follows:

Protein protean → metaprotein → proteose → peptone →Polypeptides → lower peptides → amino acids

  (a) Primary derivative
The compound is obtained by the action of acid, alkali, and heat on proteins. Example: Fibrin from fibrinogen.

  (b) Secondary derivative
Derivative obtained by hydrolysis of peptide bonds. Example: Proteoses, peptones, peptides. 

  • Manufactured when hydrolysis is continued even after meta-protein formation.
  • Soluble in water. 
  • Do not coagulate in heating. 
  • Show toxic effects when injected in animals.
  • Example albiminose.

  • Produced by the action of dilute acids like HCl and H2SO4 on natural proteins. 
  • Soluble in water. 
  • Do not coagulate on heating.
  • Produced when graded hydrolysis is continued even after the formation of proteases.

  • Soluble in water
  • Do not coagulate by heat.
  • Produced by the graded hydrolysis.

Importance of proteins in our body

Remember, every protein in cells is synthesized according to the coded information of a single gene. Therefore, different types of proteins are responsible for the visible expression of various structural and functional genetic features of the body. That's why, their utility in the body is of a wide variety, as per the following description-

1. Colloidal Proteins - These proteins are relatively simple and soluble proteins, which remain dissolved in the basic liquid (water) of the protoplasm of the cells and control the physical conditions (sol and gel) of the fluid.

2. Structural Proteins - Fibrous proteins that play a major role in the formation of various organelles and connective tissues of cells. Therefore, they are essential for growth and repair (anabolism). Collagen, elastin, and reticulin of connective tissues and keratin of skin and nails are such proteins.

3. Enzymatic Proteins - Many complex proteins act as catalysts or enzymes in metabolic reactions.

4. Regulatory Proteins - Some proteins regulate the functions of cells, such as hormones.

5. Nutrient Proteins - Proteins whose carboxyl portions, after deamination of amino acids, participate in energy production or in lipid synthesis.

6. Transport Proteins - These are proteins circulating in the blood that carry specific substances from one part of the body to another. For example, the hemoglobin of blood carries O2. Similarly, lipoproteins of blood plasma transport fats from the liver to adipose tissue and other tissues. Some proteins present in the cytoplasm transport specific molecules across the membrane.

7. Defense Proteins - They protect the body by destroying harmful substances and invading bacteria, etc. that reaches the body. These are called antibodies.

8. Nucleoproteins - They control the development and inheritance of genetic characters.

9. Contractile Proteins - These are actin and myosin proteins of the muscles that provide movement to the body and organs by contracting the muscles.

10. Fibrinogen and Thrombin - They are in the blood and prevent bleeding by forming a blood clot at the injury.

11. Acid-Base Balance Proteins - These give important support in maintaining the acid-base balance.

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