Question

Although the β sheets in many proteins are formed from a mixture of parallel and antiparallel β strands, β barrels are constructed exclusively from β strands that run antiparallel to one another. Which one of the following statements best explains this observation?

1) Peptide connections between parallel β strands would traverse the bilayer.
2) β barrels formed by mixed strands cannot have distinct surface properties.
3) Parallel β strands form β sheets in which each of the sides is hydrophilic.
4) A mixture of parallel and antiparallel β strands cannot bend to form a barrel.

Answer 1

The correct explanation for why β barrels are made of antiparallel β strands is that parallel strands would lead to unstable peptide connections traversing the bilayer, which is not conducive for the formation of a stable β barrel structure. Option 1 is correct answer.

Step-by-step explanation:

The observation that β barrels are constructed exclusively from antiparallel β strands can be best explained by the statement that peptide connections between parallel β strands would traverse the bilayer.

The formation of β barrels involves bending of β strands into a cylindrical shape, and in such a structure, antiparallel alignment allows for optimal hydrogen bonding and structural stability.

Parallel β strands, on the other hand, would result in peptide connections that stretch across the barrel, destabilizing the structure because they cannot span the hydrophobic core of a membrane bilayer effectively.

Moreover, β barrels typically span cellular membranes, and the antiparallel arrangement creates distinct interior and exterior surfaces, contributing to the functionality of these proteins in cellular contexts.

The correct option that explains this observation is: 1) Peptide connections between parallel β strands would traverse the bilayer.