The story of Protein

3D STRUCTURE OF PROTEIN 

Proteins are large biological molecules or macromolecules, consisting of one or more chains of amino acids. Protein is a polypeptide chain that made up of carbon, nitrogen, oxygen and sulphur. 

Proteins can be divided to 4 basics structures which is primary, secondary, tertiary and quaternary. 

Primary Protein Structure

• The primary structure refers to amino acid linear sequence of the polypeptide chain. The primary structure is held together by covalent bonds such as peptide bonds, which are made during the process of protein biosynthesis or translation.
• The two ends of the polypeptide chain are referred to as the carboxyl terminus (C-terminus) and the amino terminus (N-terminus) based on the nature of the free group on each extremity. 
•  A specific sequence of nucleotides in DNA is transcribed into mRNA, which is read by the ribosome in a process called translation.
• Example: Insulin is composed of 51 amino acids in 2 chains. One chain has 31 amino acids and the other has 20 amino acids.

   Secondary Protein Structure

• Secondary Protein composed of  alpha helix and beta strand or beta sheets
• These secondary structures are defined by patterns of hydrogen bonds between the main-chain peptide groups.
• Both the alpha helix and the beta-sheet represent a way of saturating all the hydrogen bond donors and acceptors in the peptide backbone.

   Tertiary Protein Structure

• Three-dimensional structure of a single,double,or triple bonded protein molecule.
• The tertiary structure is the final specific geometric shape that a protein assumes.
• These bonding interactions may be stronger than the hydrogen bonds between amide groups holding the helical structure. 
•  Different fragments of the same chain may become bonded together.

   Quaternary Protein Structure

• Quaternary structure is the three-dimensional structure of a multi-subunit protein and how the subunits fit together.
•  is stabilized by the same non-covalent interactions and disulphide bonds as the tertiary structure.
•  called a dimer if it contains two subunits ,a trimer if it contains three subunits, and a tetramer if it contains four subunit.