Primary structure of а protein

• The primary structure of а protein is the sequence of amino acids present in its peptide chain or chains.

• The end with the free H3N+ group is called the N-terminal

end, and the end with the free СОО- group is called the С-terminal end.

Primary structure

Secondary structure of а protein• The secondary structure of а protein is the arrangement in

space of the atoms in the backbone of the protein. Three major types of protein secondary structure are known; the alpha helix, the beta pleated sheet, and the triple helix. The major force responsible for all three types of secondary structure is hydrogen bonding between а carbonyl oxygen atom of а peptide linkage and the hydrogen atom of an amino group (-NH) of another peptide linkage farther along the backbone.

Secondary structure

Alpha Helix• The Alpha Helix The alpha helix (α-helix) structure resembles а

coiled helical spring, with the coil configuration maintained by hydrogen bonds between N – Н and С= О groups of every fourth amino acid

Beta pleated sheet• The beta pleated sheet (β-pleated sheet) secondary

structure involves amino acid chains that are almost completely extended.

 

Tertiary structure The tertiary structure of а protein is the

overall three-dimensional shape that results from the attractive forces between amino acid side chains (R groups) that are widely separated from each other within the chain.

There are four types of bonding interactions between "side chains" including: hydrogen bonding, salt bridges, disulfide bonds, and non-polar hydrophobic interactions.

Tertiary structure

Quaternary structure• Quaternary structure is the highest level of

protein organization. It is found only in proteins that have structures involving two or more polypeptide chains that are independent of each other — that is, are not covalently bonded to each other. These multichain proteins are often called oligomeric proteins. The quaternary structure of а protein involves the associations among the separate chains in an oligomeric protein.

Hemoglobin