Question

Which of the following experimental data are consistent with the conclusions of Unwin and Henderson's experiments on transmembrane protein structure?

A. Membranes undergo phase transitions that are determined by the molecular components of the membrane.

B. Biological membranes are relatively fluid structures.

C. Membrane phospholipids have more lateral and rotational freedom of movement than flip-flop movement between membrane leaflets.

D. Many transmembrane proteins are characterized by one or more transmembrane alpha helices.

Answer 1

The correct option is D. Many transmembrane proteins are characterized by one or more transmembrane alpha helices.

Henderson and Unwin are using a method for determination of the projected structures of unstained crystalline specimens. Unwin and Henderson found in their experiment that protein expands to both sides of the lipid bi-layer. It is composed of seven α-helices packed and run perpendicular to the plane of membrane. The presence of the amino acid sequence together with information about the electron scattering density from the work of Henderson and Unwin, has motivated model-building efforts to fit the bacteriorhodopsin sequence information into a series of α-helical segments.