Beta ( β ) sheets are a type of secondary structure in proteins. A segment of a single chain in an antiparallel β sheet has a length of 80.5 Å . How many residues are in this segment? number of residues:

The correct answer is 23.

Explanation:

Beta sheets are a kind of secondary composition in proteins, which are formed of the beta-strands that are associated laterally by more than two hydrogen bonds. A beta chain or strand comprises three to ten amino acid residues.  

One is familiar by the fact that in case of an anti-parallel combination after every 7 angstroms there is a repeat, and per each repeat, there are 2 residues. Thus, after every 7 angstroms, 2 residues are present.  

In the given question, length of the antiparallel beta-sheet is 80.5 Angstrom = (number of segments) * (residues per segment)

= (80.5/7)*2

= 11.5*2

= 23

Hence, the number of residues in the given segment is 23.