Which is TRUE regarding protein structures?

Antiparallel β-sheets are generally considered stronger than parallel β-sheets due to the way hydrogen bonds are formed between the strands. In antiparallel β-sheets, the strands run in opposite directions, allowing for a more optimal geometry of the hydrogen bonds, which are formed between the carbonyl (C=O) groups of one strand and the amide (N-H) groups of the neighboring strand. This arrangement leads to stronger and more stable interactions.

In contrast, parallel β-sheets have strands that run in the same direction. Consequently, the hydrogen bonds in parallel sheets are not as linear, which can create strain and make them weaker. The less optimal hydrogen bonding geometry in parallel sheets contributes to their lower overall stability compared to antiparallel sheets.

Through this understanding, it is clear why the assertion regarding antiparallel β-sheets being stronger than parallel β-sheets holds true in the context of protein structures.