The word protein is derived from the Greek word proteios. Protein means most important. Numerous amino acids linked together by peptide bonds form large molecules with high molecular weight called proteins. Protein is called the workhorse of life. Proteins have acidic and basic properties and are called amphiteric molecules. Dutch chemist G. Mulder (1839) was the first to use the term protein. One of the components of protoplasm is protein. Proteins are made up of 20 types of amino acids. 12% of the body is protein. 50% of the dry weight of cells is protein.
Characteristics of protein
1. Proteins are made up of carbon, hydrogen, oxygen and nitrogen.
2. Protein contains sulphur, phosphorus, iron and copper.
3. Changes in the physical and chemical nature of proteins.
4. Proteins are tasteless or colorless biochemical substances.
5. Some proteins are soluble in water and some are soluble in salt.
6. Some dissolve in alkali or acid solution and some in alcohol solution.
7. Proteins are colloidal in nature.
8. Proteins are large and high molecular weight organic compounds.
9. Their molecular weight is 5,000-50,000,000 daltons. The molecular weight of insulin is 6,000 daltons.
10. Hydrolysis of proteins by proteolytic enzymes yields amino acids.
11. Proteins are amphoteric because they contain basic groups and acidic groups. It is called an amphoteric protein for having both acidic and alkaline properties.
12. Addition of ninhydrin to the protein solution gives a red color when heat is applied.
13. Application of acid causes proteins to precipitate or coagulate and change molecular structure.
14. It acts as an electrolyte or buffer solution.
15. Proteins are precipitated in magnesium sulfate and sodium sulfate solutions.
16. Protein breaks down in the presence of oxygen to produce NH3, CO2 and H2O.
17. Proteins can be degraded in different ways.
Sources of protein
Sources of vegetable protein are lentils, kesari, peas, chickpeas, chickpeas, mung beans, mung beans, almonds, etc. The sources of animal protein are fish, meat, milk, eggs, chickpeas, ghee, butter etc.
Expansion of protein
Proteins are present almost everywhere in the body. 50% of the dry weight of the organism is protein. Proteins are the building blocks of all living organisms. All enzymes are proteins but not all proteins are enzymes. Enzymes, hormones, antibiotics etc. that regulate biological reactions are special types of proteins. All plants and animals contain protein. Proteins exist in viruses, bacteria, blue-green algae, algae, fungi, lichens, etc.
Structure of Protein
Many amino acids are linked by peptide bonds to form proteins. 20 types of amino acids participate in the formation of proteins. Amino acids join together to form polypeptide chains. Polypeptides are the basic building blocks of proteins. One or more polypeptide chains join together to form a protein. Proteins are called polypeptide compounds because they contain peptide bonds. A polypeptide chain consists of at least 50 amino acids. The small protein insulin is made up of 51 amino acids and the large protein titin is made up of 40,000 amino acids. Albumin protein contains 582 amino acids.
Lysozyme is a protein made up of a polypeptide.
Proteins made up of two polypeptides are integrins.
Collagen is a protein made up of three polypeptides.
Hemoglobin is a protein made up of four polypeptides.
There are four types of protein structure. These are-
1. Primary structure: The primary structure of protein is chain shaped. Insulin is the primary protein.
2. Secondary structure: The secondary structure of protein is coiling and folding. It consists of α-helix and β-pleated chains. Silk and keratin proteins are secondary structures.
3. Tertiary structure: Tertiary structure of protein is three dimensional. Fibrinogen protein is of tertiary structure.
4. Quaternary structure: Two or more polypeptide chains joined by disulfate or hydrogen bonds to form a protein is called quaternary structure. It is a quaternary structure. Hemoglobin is quaternary protein.
Structural classification of proteins
Proteins are of three types based on structure.
(i) Fibrous protein: Proteins with long and parallel polypeptide chains are fibrous proteins
says For example, collagen, elastin, keratin, fibrin etc.
(ii) Globular protein: Globular protein is called globular protein. Eg- serum, globulin, insulin, myoglobin, hemoglobin, alkaline phosphatase, cytochrome-c etc.
(iii) Intermediate protein: Fibrous protein is called intermediate protein. For example, fibrinogen.
Classification of proteins based on function
Proteins are of two types based on function.
(i) Structural protein: All the proteins that make up the organism’s body are called structural proteins. E.g. Keratin (skin, hair, horns, nails, scales, feathers), collagen (bones, tendons, connective tissue), keratin (insects), sein (bone), fibrin (silk, spider webs), chondrin (cartilage) ), skerroprotein (insect exoskeleton) etc.
(ii) Functional protein: Those proteins that cause the metabolism of the organism are called functional proteins. These are called regulatory proteins. For example, enzymes, hormones, vitamins, respiratory etc.
Conformational classification of proteins
Proteins are of two types based on shape.
(i) Fibrous protein: The protein in which several polypeptide chains join together to form a fiber-like structure is called fibrous protein. They are insoluble in water because they contain hydrophobic amino acids. It provides mechanical and structural support to the organism. For example, fibrin, collagen, elastin, α-keratin etc.
(ii) Rounded protein: The protein which has round structure is called round protein. Most proteins in living organisms are globular proteins. Tertiary and quaternary structures are globular proteins. It is soluble in water, but insoluble in organic solvents. It provides mechanical and structural support to the organism. For example, myoglobin, hemoglobin, cytochrome-c etc.
Characteristic classification of putin
Proteins are of two types based on properties.
(i) Complete protein: The protein that contains all the amino acids required by the body is called complete protein. For example – casein, albumin, erachin etc.
(ii) Incomplete protein: The protein that does not contain all the amino acids required by the body is called incomplete protein. For example, vegetable protein.
Polypeptide-based classification of proteins
Proteins are of different types based on the polypeptide chain.
(i) Monomeric protein : The protein which is made up of one polypeptide chain is called monomeric protein. For example, myoglobin.
(ii) Dimeric protein : The protein which is composed of two polypeptide chains is called dimeric protein. eg transamylase.
(iii) Trimeric protein : The protein which is made up of three polypeptide chains is called trimeric protein. For example, Hemerythrin.
(iv) Tetrameric protein: Proteins which are made up of four polypeptide chains are called tetrameric proteins. For example, hemoglobin.
(v) Polymeric protein: Proteins which are made up of several polypeptide chains are called polymeric proteins. For example, insulin.
Functionality based classification of proteins
Proteins are of different types based on function.
(i) structural proteins, (ii) regulatory proteins, (iii) transport proteins, (iv) storage proteins, (v) inhibitory proteins, (vi) membrane proteins, (vii) contractile proteins, (viii) toxic proteins and (ix) ) enzyme protein
Simple protein
Proteins that can be hydrolyzed by acid or enzyme to obtain only amino acids are called simple proteins. Simple proteins are divided into seven categories based on solubility.
1. Albumin: Proteins that dissolve easily in water and form a cloudy solution are called albumin. It dissolves in water and a weak salt solution. It coagulates on application of heat. It is widely available in nature. Their molecular weight is 45000-65000 daltons. This protein is found in egg whites, plasma, milk, leaves and seeds. For example, ovalbumin (egg white, 10-12%), beta-amylase (barley, barley), lactoalbumin (milk), serum-albumin (blood and lymph 4-5%), legumin (pea), leucosin (wheat, algae), ligumelin (bean), myo-albumin (muscle), myosin (muscle) etc.
2. Globulin: Globulin is insoluble in water but soluble in weak salt solutions. It coagulates in heat. It is stored as stored food in seeds. However, this protein is also found in animal bodies. Their molecular weight is 3500 daltons. It is present in egg yolk, plasma and semen. Eg- phosvitin (yolk), ovoglobin (egg yolk), tuberin (round potato), lactoglobin (milk), ovoglobin (seed), alphaglobin (blood), serumglobin (blood), myosinogen (muscle), pseudoglobulin (chick/whey). , glycine (soybean), pomelin (orange), erachin (peanut), legumin (pea), edestin (cotton/shaan), crystallin (eye lens) etc.
3. Glutelin: Glutelin is insoluble in water, but soluble in mild acids and alkalis. It does not coagulate in heat. It is present in plant grains. Animals do not contain glutelin. Eg – Glutenin (Wheat/Bhutra), Origenin (Rice) etc.
4. Protamine: Protamine is the smallest protein. It is soluble in water, weak acids and ammonium hydroxide. It does not coagulate in heat. Their molecular weight is 5,000 daltons. This protein is found in the nucleus of some fish sperm. For example, clupine (herring), arginine (rice), salmin (salmon), cyprinine (carp), stearine (sturgeon) etc.
5. Prolamine: The protein which hydrolyzes to produce large amount of proline and ammonia is called prolamine. It is insoluble in water. But 70-80% soluble in ethyl alcohol. They do not coagulate in heat. It is found only in the seeds of plants. Animals do not contain prolamin. Eg – gliadin (rice/rye/wheat), zein (bhutra), hordin (barley/barley) etc.
6. Histone: Histone protein is composed of several basic amino acids. It is soluble in water, but insoluble in ammonium hydroxide. They do not coagulate in heat. It is located in the nucleus or chromosomes. Chromosomes contain histone proteins H1, H2, H3, H4 etc. Histones play an important role in gene expression. For example, arginine, lysine, nucleohistone, globin etc.
7. Scleroprotein: This protein is insoluble in water, salt, acid and alkaline solutions. It is called ‘animal skeletal protein’. This protein is not present in the plant body. Lives only in animal bodies. It has no action on enzymes. It is found in animal bones, hair, nails, horns, skin, hoofs etc. Eg- keratin (skin, nails, hair), collagen (skin), tendon (bone), elastin (ligament), fibroin (silk) etc.
Conjugated Protein
Proteins in which amino acids and other components can be found on wet analysis are called conjugated proteins. A conjugated protein consists of two parts. Protein part and non-protein part. The protein part is called apoenzyme and the non-protein part is called prosthetic group. Conjugated proteins depending on the prosthetic group are:
1. Nucleoprotein: All the proteins that are made up of amino acids and nucleic acids are called nucleoproteins. All these proteins are located in chromosomes. It is soluble in water. These proteins are found in cell nuclei, viruses and ribosomes. For example, chromatin.
2. Glycoprotein: All the proteins that are made up of amino acids and sugars or glucose are called glycoproteins. If these proteins contain fructose instead of glucose, they are called mucoproteins and if they contain galactose, they are called galactoproteins. It is soluble in alkali. Cell membranes, jellyfish and saliva contain this protein. Eg- thyroglobin (thyroid), plasma glycoprotein (liver), immunoglobulin (blood cells), ribonuclease (RNA), deoxyribonuclease (DNA), mucin, peptidoglycan (bacteria), ovoalbumin (ovum).
3. Lipoprotein: The organic compound formed by the combination of protein and lipid is called lipoprotein. It is soluble in water, but insoluble in organic solvents. It forms the membranes of different types of cells. There are 5 types of lipoproteins. Chylomicrons, VLDL, LDL, IDL and HDL.
4. Phosphoprotein: All proteins that are formed by amino acids and phosphate or phosphorus are called phosphoproteins. It is insoluble in water, but soluble in organic solvents. E.g. Casein (Milk), Ovovitelin (Egg) etc.
5. Chromoprotein: Prosthetic group of proteins formed by dyes is called chromoprotein. Eg- Bilirubin, Chlorophyll, Hemoglobin, Carotenoids, Flavoprotein, Rhodopsin, Biliprotein, Myoglobin, Cytochrome, Hemocyanin etc.
6. Metalloprotein: The prosthetic group of protein which is formed by any metal (Fe, Mn, Mg, Zn, Cu, Co, Mo) is called metalloprotein. Such as siderophyllin, ceruloplasmin, ferridoxine, cytochrome, oxidase, ferritin, nitrogenase, hemoglobin etc.
7. Flavoprotein: The protein which is attached to flavin compound (FAD) is called flavoprotein. Eg- Sulfide reductase, succinate dehydrogenase, NADH-dehydrogenase etc.
8. Porphyrin: The protein that porphyrin is associated with iron or cytochrome is called porphyrin or cytochrome protein. E.g. Cytochrome-b.
Protein Derivatives
Proteins that are produced from compound proteins are called produced proteins. All these proteins are produced from natural proteins due to enzymes, acids, alkalis or heat. Proteins produced are of two types. Primary produced proteins and secondary produced proteins.
1. Primary produced protein: The protein that is formed under the influence of acid or enzyme is called primary produced protein. The primary proteins produced are:
(i) Proteins: Proteins are formed by the reaction of dilute acids, enzymes and water. It is insoluble in water. Edestin to edestan, myosin to myosin, fibrinogen to fibrin, etc.
(ii) Metaprotein: Metaprotein is insoluble in water. But soluble in mild acid and alkali. For example, acid metaprotein, alkaline metaprotein etc.
(iii) Denatured protein: Denatured protein is produced by the effect of heat or alcohol on the protein. It is insoluble in water. For example, the white part of the coagulated egg.
2. Secondary produced protein: The protein that is formed by wet analysis of protein is called secondary produced protein. Secondary produced proteins are:
(i) Protease: Protease is formed by the action of pepsin and trypsin. It is insoluble in water. But stored in heat. Albuline produces albumose and globulin produces globulose.
(ii) Peptone: Peptone is formed by the action of mild acid and enzymes. It is insoluble in water. Does not coagulate in heat. Ammonium sulfate does not precipitate in solution.
(iii) Peptides: Peptides consist of a small number of amino acids. Amino acids join together to form dipeptides, tripeptides and polypeptides. It is soluble in water. For example, glycine-alanine, leucine-glutamic acid.
(iv) Infraproteins: These are metalloproteins. eg metaprotein.
(v) Coagulated protein: This protein is produced when blood clots.
Proteomes
All the proteins produced by the cells, tissues and organs of an organism are collectively called the proteome. Different types of proteins can be produced from different cells, tissues and organs of an organism. So the proteome is variable, but the genome is not.
Ideal protein
Eggs and milk contain ideal proteins. So eggs and milk are considered ideal proteins. Fish and meat contain less than ideal levels of tryptophan. Pulses contain less than ideal levels of methionine and tryptophan. Pulses have less protein content.