Do these notes explain What is Protein and the classification of proteins in Biochemistry?

The proteins are the cellular macromolecules most abundant constituting 60% of the dry weight of cells.

They consist of one or more polypeptide chains and has a molecular weight greater than 10,000.

They have a unique and diverse structure. The polypeptide chains fold more or less heavily on themselves inducing a large number of different three-dimensional structures.

It is this that is causing a variety of function allowing them to be responsible for thousands of reactions in a different cell. Their name “Nano-machines” cell is thus justified.

For the wide variety of cellular responses, we can easily imagine that the number of different proteins known to date is very important: 60,000.

classification of proteins
Proteins classification

Proteins are derived from the translation and transcription of genes, their synthesis is under genetic control.

All proteins are made ​​up of amino acids (20 amino acids, of course on amino acids ) but they do not have of biological activity. Amino acids are the alphabet of the protein structure.

The sequence of these amino acids can be achieved by an almost infinite number of sequences to form an equally infinite number of different proteins

Ways of Classification of proteins?

According to the classification of proteins, these are again classified into forms, functions, and composition.

1. Classification of proteins based on the structure

a. Fibrous Proteins

In this classification proteins, The polypeptide chains are elongated and wound about an axis in a helical shape. These are structural proteins. They can be extracellular and will then be insoluble in water and have a protective function:

  • α keratin hair
  • fibroin silk
  • elastin of the skin
  • collagen tendons

They can also be intracellular include myosin and tropomyosin muscle cells. careful not to confuse fibrous and filamentary (globular proteins attached to each other).

fibrous and myoglobin protein

b. Globular proteins

Soluble in water, they are spherical. They have much more complex than the fibrous protein structure, but they have a much greater variety of biological activities. The best example of Globular protein is MyoGlobin.

They can be membrane and then have roles as:

  • Carrier
  • Receptors
  • Ion channel
  • GAP links
  • Cell adhesion proteins

They may be soluble and be plasma such as albumin, protein hormones such as LH, cytosolic proteins circulating proteins such as Calmodulin.

2. Classification of proteins based on function

They may be involved in:

  • The structure and support is the case of collagen, elastin, glycoproteins membrane
  • The contraction: actin, myosin
  • The cell adhesion proteins such as GAP junctions and proteins such as cadherin,
  • The reception signal such as membrane insulin receptors or intracellular steroid receptors
  • The signal transduction, a typical example being formed by the membrane protein G (see the course on cellular communication )
  • a signal: they can be informative molecule as growth factors (EGF) and Follicular stimulating hormones (FSH),
  • the immunity, the role of  immunoglobulin
  • the transportation such as haemoglobin (O 2 ) and transferrin (iron)
  • the catalysis: therefore these proteins also play a role in metabolism, replication and DNA transcription, muscle contraction, cell signalling.

3. Classification of Proteins Based on Composition

If they are carbohydrates that are added in an amount between 5 and 40% of the molecule, the protein is called glycoproteins and glycosylated proteins. If the proportion of carbohydrates to pass more than 90% of the molecule, one blade of peptidoglycan, they have passive protection.

  • There are two main types of proteins. Those containing only amino acids are holoproteins.
  • Those containing a protein moiety (the apoprotein ) and a non-protein portion are hemoproteins.
  • Both parts are linked in various ways: covalent bonds, ionic, hydrogen, hydrophobic. This non-protein portion may be a group prosthetic ( inducing the emergence of new biological properties setting, as heme in haemoglobin).
  • The element can be added to one or more metal cofactors (Cu, Zn, …) that metalloprotein.
  • A chromoprotein contains a pigment and a phosphoprotein comprises one or more inorganic phosphates.
  • Also exist nucleoproteins by adding acid nucleic, and lipoproteins by addition of lipids.

4. Classification of Proteins based on solubility

The different globular proteins can be classified based on their solubility in different solvents, such as water, salt, and alcohol.


Proteins are high molecular weight biological macromolecules. No in this article I provided “what is proteins and Classification of proteins”. The Classification of proteins is explained based on the structure, composition, and function. Please share this important article on What are Proteins and the classification of proteins? 

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *