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Q5 - Mapping Membrane-Protein Topology with Protease Protection

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Plasma Membrane Structure & Transport

Imagine you are studying a membrane protein represented in the diagram below. You prepared artificial vesicles containing this protein only in the membrane. The vesicles were then treated with a protease cleaving close to the membrane (2) or permeabilised before protease treatment (3). Resulting peptides were subsequently separated using SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis).

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. The bigger fragments in lane 3 are hydrophilic.
B. The smaller fragments in lane 2 represent protein domains protruding outside the membrane.
C. Domain a is rich in leucine or isoleucine.
D. Domains a, c and e protrude into the lumen of vesicles.
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Question reproduced from IBO 2016, Theoretical Paper A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)