Question

Porin proteins—which form large, water-filled pores in mitochondrial and bacterial outer membranes—fold into β-barrel structures. The amino acids that face the outside of the barrel have what kind of side chains?

Choose one:
A. amphipathic
B. hydrophobic
C. polar
D. charged
E. hydrophilic

Answer 1

The amino acids on the outside of porin proteins have hydrophobic side chains, which interact with the interior of the phospholipid bilayer and stabilize the protein within the membrane.

Step-by-step explanation:

The amino acids that face the outside of the porin proteins — which form β-barrel structures in mitochondrial and bacterial outer membranes — have hydrophobic side chains. This is because hydrophobic amino acids interact with the hydrophobic interior of the phospholipid bilayer. They avoid contact with the aqueous environment which is favorable for the stability of the membrane protein structure. These hydrophobic residues help anchor the protein within the membrane. In contrast, hydrophilic amino acids are usually found lining the pore of the protein that interacts with water and charged particles, facilitating the passage of ions and polar molecules across the membrane.