Covalent bond is formed between two cysteine amino acid residues; as a result, disulphide bonds are formed. An example is cystine.
When a group containing a hydrogen atom is covalently bonded to an electronegative atom, such as O2 or nitrogen favours hydrogen bonding. A hydrogen bond is formed when an H2 atom shares electrons with two neighbouring atoms, that is, oxygen and nitrogen. Example: Hydrogen atom of one peptide shares its electron with the carbonyl atom of another peptide.…
Electrostatic bonds are formed when two oppositely charged groups come close together and attract each other. Example: Divalent cations like Mg2+ may form electrostatic bonds with two acidic side chains. Interaction between acidic and basic groups of amino acid: The R—group of glutamic and aspartic acid contributes negatively charged carboxylate groups, and the basic amino acids (arginine,…
As polypeptide folds, hydrophobic R—groups are brought into close proximity as they are excluded from water. Many amino acids like valine, alanine, leucine, isoleucine, methionine, tryptophan, phenylalanine, and tyrosine have side chain or R groups which are hydrophilic. These R—groups combine together with the removal of hydrogen and form linkages between various segments of chains.…
The term tertiary structure refers to the unique three-dimensional confirmations that globular protein assumes as a consequence of the interaction between the side chains in their primary structure. Tertiary structure has several important features. The amino acids that are distant from each other in the primary structure come closer during the formation of the tertiary structure. As…
The polypeptide chains are arranged in the same direction if the N-terminal ends of all the participating polypeptide chains lie on the same edge of the sheet with all C-terminal ends on the opposite edge. In other words, the hydrogen-bonded neighbouring polypeptides are aligned in the same direction of the N— to —C terminals. Parallel…
β-pleated sheets form when two or more polypeptide chain segments line up side by side. Each individual segment is referred to as β-strand. Rather than being coiled, each β-strand is fully extended. β-pleated sheets are stabilised by hydrogen bonds that are formed between the polypeptide backbones N—H and carbonyl group of adjacent chain. There are…
α-helix is spiral in shape and has a rigid arrangement of polypeptide chain as proposed by Pauling and Corey (1981). The salient features of α-helix are as follows: Figure 3.5 Structure of α-helix
The protein gets folded, and the hydrogen bonding between the neighbouring amino acids results in the formation of a rigid and tubular structure called helix. This constitutes the secondary structure of proteins. Two types of secondary structure, α-helix and β-sheet, are mainly identified.
The primary structure of protein refers to the number sequence of amino acids and the constituent units of polypeptide chain. The main mode of linkage of amino acids in proteins is the peptide bonds which link the α-carboxyl group of amino acid residue to the α-amino group of the other. Linus Pauling and Robert Corey…