Final answer:
Porin proteins form barrel-like channels in membranes and are composed primarily of β sheets, not α helices. They allow molecules to pass through due to their structure of alternating hydrophobic and hydrophilic amino acids.
Step-by-step explanation:
Porin proteins are integral membrane proteins that create large, barrel-like channels in the membrane. These channels are characterized by specific structural features that allow them to perform their function. The statement '(a) They are made primarily of α helices' is not true about porin proteins. Instead, porin proteins are primarily composed of β sheets that form the barrel structure, allowing molecules to pass through the membrane.
These proteins are designed with alternating hydrophobic and hydrophilic amino acids to ensure proper insertion and function within the membrane. Porin channels do not form narrow channels; they allow for the passage of small molecules and ions. These structures have hydrophilic domains that are exposed to the intracellular and extracellular fluids, while the hydrophobic domains interact with the lipid bilayer.