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 256 Å. How many residues are in this segment?

3.14 residues

Explanation:

This kind of sheets has the particularity that the distance between adjacent residues is 3.5 Angstroms. Furthermore, there are two residues per cycle.

Hence, we can calculate easily the number of residues in a segment, by using the expression:

Nr = (256 Å) / (3.5 Å/residue) = 3.14 residues

I hope this is useful for you

Regards