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 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 . 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
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Ways of Classification of proteins?
According to classification of proteins, these are again classified into forms, functions and composition.
1.1. Classification of Proteins on the Basis of Structure:
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).
1.1.2. Globular proteins:
Soluble in water, they are spherical . They have a much more complex than the fibrous protein structure, but they have a much greater variety of biological activities. 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 .
1.2. 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 membrane insulin receptors or intracellular steroid receptors,
- the signal transduction , a typical example being formed by the membrane protein G (see course on cellular communication )
- a signal : they can be informative molecule as growth factors (EGF) and Folicular stimulating hormones (FSH),
- the immunity , the role of immunoglobulin
- the transportation such as hemoglobin (O 2 ) and transferrin (iron)
- the catalysis : therefore these proteins also play a role in metabolism, replication and DNA transcription, muscle contraction, cell signaling …
1.3. Classification of Proteins Based on Composition:
- 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 heteroproteins .
- 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 hemoglobin ).
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 a passive protection.
- The element can be added 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.
Proteins are high molecular weight biological macromolecules. No in this article i provided “what is proteins and Classification of proteins”. The Classification of proteins are explained based on the structure, composition and function.
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