Protein : Structure, Functions, Properties and Role

Published on 23-Sep-2022


The origin of the word Protein is from the Greeks, who first named it ''Proteles''. "Proteles" means the most important, which shows the essentiality of Protein. Protein is a fundamental biochemical substance or molecule required for all living organisms. Different amino acids are chained in various ways to form a single protein molecule. The word ''protein'' was first discovered by the popular G. Mulder back in the year 1839.

Proteins are large complex organic molecules and are composed of numerous amino acids. In other words, Protein is a high molecular, biochemical substance with a large weight that produces amino acids through hydrolysis. The polymer of amino acids is known as Protein (or non-protein). Hundreds of different proteins are produced and stored inside a cell all the time. Many molecules of amino acids are joined together by peptide bonds to form a single protein molecule.

Proteins are present almost everywhere in the bodies of organisms. Proteins exist as essential structural elements in all parts of the body. Enzymes, antibodies, and hormones that control all the bio-reactions inside us are also proteins. All enzymes are made of different proteins, but not all proteins are enzymes. About 50% / half of the dry weight of an organism is Protein.

Structure of a protein molecule:

Different amino acids are chained in different ways to form a protein. The amide bond formed by an amino acid's carboxyl group (COOH) with the -amino group of another amino acid is called a peptide bond. One molecule of water is released for each peptide bond formed. Two amino acids join together to form dipeptides, three join together to form tripeptides, and four to ten join together to form oligopeptides. Peptide bonds bind about 50 molecules of different amino acids, and proteins are polypeptide compounds.

Meanings of polypeptide and Protein:

Polypeptide: Peptides containing more than 50 amino acids.

Protein: In simple words, proteins are one or more polypeptides folded into a specific three-dimensional shape. Proteins are functional only when the folded state or portion is achieved.

Variation: Every organism has numerous types of proteins inside their bodies. An organism contains at least as many proteins as the number of genes expressed. So, thousands of proteins can exist in a living organism's body. Again, since there are various genetic differences between the two species, there are also protein type differences. Two organisms of the same species may have some differences, so even two organisms of the same species will have structural differences in proteins.

Site of Synthesis: Proteins are synthesized in cellular ribosomes during protein synthesis.

Properties of proteins

  • 1. Proteins are colloidal, primarily calcareous.
  • 2. The hydrolysis of proteins yields amino acids with acids, bases, and enzymes.
  • 3. Various physical and chemical processes can easily alter or bring changes in the nature of proteins.
  • 4. Proteins are soluble in water, weak acids, alkalis and mild salt solutions but are insoluble in alcohol.
  • 5. It is composed of carbon, hydrogen, oxygen and nitrogen. It also contains Sulphur, iron and copper
  • 6. Application of acid causes the proteins to precipitate or coagulate. It also changes the molecular structure of a protein inside our bodies.
  • 7. Proteins usually act as electrolytes and buffer solutions inside our bodies.
  • 8. Proteins exhibit basic and acidic properties as the monomer amino acids contain primary groups (– NH2) and acidic groups (-COOH). That is why it is called amphoteric Protein.


About classification of proteins

Types of Protein: 

There are three thousand types of proteins in a cell of Escherichia coli that are inside living organisms. There are about 100,000 types of proteins in the human body that are different from the proteins of E. coli.

The functions of Protein

1. It acts as a structural component of the body, such as collagen and many more.

2. Proteins act as stored food in cells and produce energy when the body needs it.

3. It plays a vital role in forming various organelles and cell membranes.

4. As an enzyme, it regulates the body's reactions and temperatures and keeps the body moving, such as Rubisco.

5. As the building block of antibodies, the body's immune system is built and keeps the body free from diseases, such as immunoglobulins.

6. It produces hormones the body needs, such as insulin and many other essential hormones.

7. Histone proteins activate the nucleus and the nucleic acids inside our bodies.

8. Some proteins are poisonous, and many organisms die from eating them (snake venom proteins).

9. Plants that contain toxic proteins protect them from attack by many animals and birds.

10. The hemoglobin protein transports O2 gas to all cells in the body for respiration.

11. Proteins produced from peptides in the human body act as defensive antibodies.

12. It acts as a pigment inside our body, e.g., rhodopsin.

13. Interferon is a cellular protein, and it is produced spontaneously in the body when a virus attacks it. It is believed that interferon can be used to treat cancer and viral diseases.

14. One gram of protein oxidation produces about 4.1 kcal of energy.

Role of Protein in Living Body

 1. Role of Enzymes: All reactions inside the organism are controlled by specific enzymes. And all enzymes are proteins, but all proteins are not enzymes. Enzymes act as biocatalysts to increase the rate of biochemical reactions that are essential for living organisms.

2. Replenishment and growth: Protein is essential for the recovery and development of the body. Proteins are required to meet the bodily losses incurred to carry out various biological functions, such as respiration, excretion, reproduction, etc. 

3. The structural role of Protein: Fibrous proteins make up the lining of various organs, acting as a link between different tissues works. A protein known as collagen is the main component of tendons that connect muscles to bones.

4. Transportation: Transport of various molecules inside the cell, transport of ions etc., inside our bodies. Besides, the type of Protein called hemoglobin supplies O2 to all the body's cells.

5. Organism: Hormones control organisms' growth and development. Hormones are made up of particular types of proteins. Certain hormones, such As insulin, somatotrophic hormone (STH), luteinizing hormone (LTH) etc.

6. Poisoning and self-defence: Metabolic processes in various organisms produce toxic substances from proteins. These substances are helpful for the organism's self-defence—for example, snake poison or venom, which is used for the self-defence of snakes.

7. Viruses and Cancer Prevention: Viruses have been identified as the cause of various types of cancer. A particular protein called interferon is used to treat blood cancer as an anti-virus.

8. Production of Antibiotics: Antibiotics are used to treat various diseases. These antibiotics are produced by metabolic reactions in organisms, especially microorganisms.

9. Immunity: Antibodies produced in the host body to destroy and control pathogens are also proteins. It also acts as a pain reliever: Endorphins produced in the brain are used as pain relievers.

10. Inducing sleep: The most recently discovered sleep-inducing s-factor proved to be a particular type of Protein.

Protein in the diet

It is essential to have protein foods in our diet because the role protein plays in our diet is vital to building the body. Different types of food contain different amounts of protein; some have a lot of protein, while others don't. Pulses contain the most protein in terms of quantity, but nutritionists still prefer animal protein.

Protein is made up of twenty types of amino acids, and these twenty types of amino acids are essential as structural units. According to the human body's needs, only eight amino acids are: leucine, isoleucine, lysine, methionine, thionine, valine, phenylalanine, and tryptophan, are called essential amino acids. It is because the other 12 amino acids can be synthesized in our body, but these eight amino acids are not synthesized in the body. They are taken into the body through the food that we eat. Arginine and histidine are essential for the bodies of children.

Not all proteins contain all the amino acids, so proteins that have all the essential amino acids should be prioritized in the diet and taken in the right amount for a healthy body. Animal proteins found in fish, meat, milk, eggs, etc., are essential, and vegetable proteins (such as pulses) are also needed for a healthy diet.

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