Primary Secondary Tertiary Quaternary

Primary Secondary Tertiary Quaternary

Structure

Arrangement of amino acids, their numbers and nature in poly peptide chain makes up for the primary structure of proteins. Covalent peptide bond is only type of bond in the primary structure of protein. Peptide bond is resonance stabilized.

The configuration of polypeptide chain can be determined if the value of φ and Ψ for each amino acid residue are known. In a fully stretched polypeptide chain amino acid residues are known.

Certain combinations are not possible due to stearic reasons.

Tertiary structure of protein is three dimensional picture of protein which depends upon folding (or coiling) of long polypeptide chain. Thus tertiary structure gives an account of actual shape of a protein.

Several identical or non-identical polypeptide chain may be linked together to form protein. Individual polypeptide chain is known as subunit. Each sub-unit has its own primary, secondary and tertiary structure.

Charact.

If even a single amino acid in a protein is replaced its properties are totally changed Secondary structure of protein deals with conformation of peptide chain present in protein molecule. There are two important possible ways in which peptide chain is arranged viz. α-helix and β-conformation or pleated sheet.

may be determined by X- ray analysis, light-scattering, diffusion, viscosity determination, ultra centrifuge method and electron microscopy. Oligomeric proteins can be composed of multiple identical polypeptide chains or multiple distinct polypeptide chains.

Polypeptide chain from hemoglobin:

His- Val - Leu- Leu - Thr - Pro - Glu - Glu – Lys

intra molecular forces and electrostatic fores as well as intermolecular forces. involves forces like hydrogen bonding, ionic, chemical and hydrophobic bonds. Proteins with identical subunits are termed homo-oligomers. Proteins containing several distinct polypeptide chains are termed hetero-oligomers.

Polypeptide chain from hemoglobin - s

His- Val - Leu- Leu - Thr - Pro - Val - Glu - Lys

Stability of ±helix is due to resonance between -C=O and N-H group. Besides hydrogen bonding, ionic, chemical and hydropholic bonds other types of bonds like disulphide bonds are also present in tertiary structure of protein.

Hemoglobin, the oxygen carrying protein of the blood, contains two α and two β subunits arranged with a quaternary structure in the form, α2β2.

References

Proteins and Structures." The Medical Biochemistry Page. Org. Of Biochemistry, 12 July 2010. Web. 28 Jan. 2013. <http://themedicalbiochemistrypage.org/protein-structure.php#primary>.

"Structures of Proteins." Tutor Vista. Four Levels Of Protein Structure, 25 Sept.

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