The protein that does not contain all the amino acids required by the body is called incomplete protein. For example, vegetable protein.

The protein that contains all the amino acids required by the body is called complete protein. For example – casein, albumin, erachin etc.

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.

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.

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.

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.

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.

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.

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.

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.