Question

1. Regarding protein structure:

1a) Why are a-helices and b-sheets particularly common (whereas, for example, each protein has its own unique tertiary structure)? 1b) What is the difference between protein domains and protein subunits?

Answer 1

Ans 1)beta sheets are extended form of helices. And alpha helices are most common secondary structure found in nature. Both of them maximize the hydrogen bonding.In the alpha helix CO of nth residue interacts with NH of n+4 residue.Beta sheets is extended form of alpha helix and it is parellel and antiparellel sheets.beta sheets have rise of 3.2 A to 3.5 A ( angstrome) per residue.valine ,isoleucine and tyrosine are beta sheet stablizer. Glutamic acid ,methaonine and alanine are alpha helix stablizer. Glyine and proline are beta and alpha helix destablizer.

Domain is the teritary structure and subunit is the quaternary structure. Domains are formed by folding of a segment of polypeptide which may or may not have functional evolutionary concerned. Quaternary structure are characterize by presence of different subunits.subunit may be of homomorphic or hetromorphic.