Proteins have levels of structure?

Posted: April 2, 2013 in Proteins
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They do, in fact there are four levels of protein structures: primary, secondary, tertiary and quaternary.

Primary structure of proteins.


Fredrick Sanger was the first scientist to discover the primary structure of proteins, by looking at the protein, insulin. The specific sequence of amino acids in a polypeptide chain is known as the primary structure of proteins. Peptide bonds are the only bonds involved in this sequence.

Secondary structure of proteins.


Secondary proteins, are the shape taken up by the polypeptide chain due to hydrogen bonding. The two most common shapes of secondary proteins are the α-helix and the β-pleated sheets.

An α-helix chanin twist every 3.6 amino acid. It is formed due to the formation of hydrogen bonds  between the CO of one amino acid to the NH of the fourth amino acid.

β-pleated sheet are formed among adjacent polypeptides chains. Like α-helices, hydrogen bonds form between the CO and NH of neighbouring chains, which results in a stronger, yet less elastic structure.


Tertiary structure of Proteins.

Three types of bonds, formed between R-groups, are responsible for the shape of these proteins. These bonds are hydrogen bonds, ionic bonds, and disulphide bonds.

Hydrogen bonds, most common, is formed when an electronegative oxygen is attracted to the electropositive hydrogen of another R-group.


Ionic bonds are formed between an charged amino acid and carbonyl group.


Disulphide bond is a covalent bond formed through oxidation of two -SH groups.


These bonds cause proteins to fold into compact, globular shapes. These proteins are soluble and are called globular proteins, for example, insulin is a globular protein.

Note: Proteins such as keratin or collagen are insoluble and do not fold into tertiary structures, instead they remain unfolded into non-fibrous structures. These are called fibrous proteins.


Quaternary structure of proteins.

Quaternary structure of proteins is the combination of two or more proteins. An example of this type of structure is haemoglobin, which is a combination for four proteins.



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