34 - AIIMS november 2002 biochemistry mcqs

1q: an alfa helix of a protein is most likely to be disrupted if a missense mutation introduces the following aminoacid with in the alpha helical structure ?

a. alanine
b. aspartic acid
c. tyrosine
d. glycine

answer b . aspartic acid

explanation : alfa helix of a protein can be disrupted due to the introduction of the following aminoacids :

1. proline : the imino group of proline is not geometrically compatible with the right handed spiral of the alpha-helix

2. charged aminoacids : glutamate ,aspartate, lysine, arginine and histidine .

3. aminoacids with bulky side chains : tryptophan

4. aminoacids that branch at the beta-carbon : valine and isoleucine .