Plantlet The Blogging Platform of Department of Botany, University of Dhaka
Proteins are the most abundant macro-molecules, occurring in each cell and each part of a cell. They are generally formed by one or more long chain(s) of amino acid residues.
Classification of protein
1) Based on source
There are two types of protein.
a) Animal protein: They are derived from animal sources. These are usually high quality protein. e.g.: eggs, milk, fish.
b) Plant protein: These are derived from plants and lower quantity protein. e.g.: legumes.
2) Based on the shape of protein molecule
These are of two type.
a) Globular protein: Polypeptide chain folded into globular form, soluble in water. E.g.: Insulin, albumin etc.
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- Soluble in water.
b) Fibrous: Polypeptide chains arranged in a long strands. e.g.: hair, skin etc.
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- Insoluble in water.
- Also called scleroprotein.
- Resistant to proteolytic enzymes.
- Examples: Collagen, actin, myosin, keratin of hair, claws etc.
3) Based on shape of composition and solubility
Three major groups are present, such as: a)simple protein, b) conjugated protein, c) Derived protein.
a) Simple protein: These are of globular type and contain only amino acids as structural components. These are further classified on the basis of solubility into several types:
| Protein name | Properties | Examples |
|
Albumins |
|
Egg albumin. |
|
Globulin |
|
Egg, milk, serum |
|
Glutelins |
|
Glutenin of wheat, oryzenin of rice |
|
Prolamines |
|
Zein of corn |
|
Scleroprotein |
|
Keratin of hair |
|
Histone protein |
|
The globin of hemoglobin |
|
Protamines |
|
Clupeine from herring sperm. |
b) Conjugated protein: They are also globular protein combined with a non protein group, called prosthetic group. These are further classified on the basis of nature of prosthetic groups present.
| Protein | Properties | Examples |
| Nucleoprotein | Have nucleic acids as their prosthetic group. | Protamins |
| Proteoglycans | Are polysaccharides combined with small amount of protein. | Mucoproteins |
| Glycoprotein | Proteins are conjugated with carbohydrates. | |
| Chromoproteins | The prosthetic group are color compound. | Flavoenzymes |
| Lipoprotein | Proteins are combined with phospholipids. | Egg yolk |
c) Derived proteins: They are products of denaturation or partial digestion of proteins.
- Proteans: Fibre from fibrinogen.
Coagulated proteins: Coagulated egg white.
Written by
Sufia Akter, B.S. (Hons), Department of Botany, University of Dhaka
Revised by
- Somudro Mahbub Nasir on 11 July 2021
