Proteins are the fundamental biological components of skin, hair, muscles, connective tissues, enzymes etc...
Proteins are defined as the biopolymers composed of α-amino acids linked by peptide bonds. They are also known as polypeptides. Proteins are the major constituents of all living organisms. They contain carbon, hydrogen, nitrogen, oxygen and sulphur.
Proteins are classified into three main groups.
The protein that yields only α-amino acids on hydrolysis is called a simple protein. Examples: albumin and globulin
The protein that yields α-amino acids and a non-protein part upon hydrolysis is called a conjugated protein. The non-protein part is called as the prosthetic group.
Based on the nature of prosthetic group, conjugated proteins are further classified as follows.
Protein associated with nucleic acids is called as nucleo protein.
Example: Histone(in DNA).
Protein containing phosphoric acid is called as phosphoprotein.
Example: casein (in milk).
Protein containing carbohydrate moiety is called as glycoprotein.
Example: mucin (in saliva)
Protein containing heterocyclic compounds like porphyrins is called as chromo protein.
Example: myoglobin (in muscle).
Protein conjugated with lipids is called lipoprotein.
Examples: chylomicron (in small intestine)
Protein containing metal ion is called as metalloprotein.
Examples: ceruloplasmin (in blood).
Protein that is derived from simple or conjugated proteins by the action of acids, alkalies or enzyme is called as derived protein. These are partially hydrolysed proteins.
Protein is termed as the building block of the body. Protein is vital in the maintenance of body tissue, including development and repair.
Some proteins acts as a hormones. Example: Insulin, a small protein, which regulates blood sugar level.
Most of the enzymes are proteins, they act as biocatalysts in chemical reactions taking place in the body.
Protein is a major component in transportation of certain molecules. For example, haemoglobin is a protein that transports oxygen throughout the body.
Proteins are used to store certain molecules. Ferritin is a protein which stores iron in the liver.
All antibodies are proteins. Antibodies neutralize infection, illness and diseases.