Chapter 11 Application

A researcher replaces many unsaturated fatty-acid tails with saturated tails of the same length. Predict the change in membrane fluidity and explain why.

Fluidity generally decreases because straighter saturated tails pack more tightly than kinked unsaturated tails.

A membrane protein contains about 20 amino acids in a hydrophobic alpha helix. What is the likely function of this region?

It can span the hydrophobic core of the lipid bilayer, with hydrophobic side chains facing the lipid tails.

A mutation disrupts the selectivity of a membrane protein's binding site. What cellular function might be affected?

Selective transport or signaling may become less accurate because the protein may no longer recognize its intended substrate properly.

A researcher adds detergent to a membrane-protein sample. Why might the proteins become soluble in water?

Detergent molecules interact with hydrophobic membrane-spanning regions and keep the proteins in soluble protein-detergent complexes.

A Golgi vesicle fuses with the plasma membrane. A protein's sugar chain originally faced the Golgi lumen. Where does the sugar chain face after fusion?

The extracellular space, because membrane orientation is preserved during vesicle transport and fusion.

A cell loses the ability to maintain phospholipid asymmetry. Name two processes that could be affected.

Cell signaling and membrane curvature or vesicle budding may be disrupted.

A drug is strongly charged and poorly lipid-soluble. Why might it cross a pure lipid bilayer less readily than a lipid-soluble drug?

The hydrophobic bilayer core is unfavorable for charged molecules, whereas lipid-soluble molecules can partition into it more readily.