Chapter 7, Problem 1Q

Summary Introduction

To review:

The evidence that suggest that protein composition in the plasma membrane of bacterial cell changes in response to changes in solute concentration of the environment.

Introduction:

Bacterial cells like Escherichia coli live in harsh conditions of the intestine in mammals including humans. When present in a hypertonic solution, the cells tend to desiccate; when present in hypotonic solution, the cells tend to swell. It was observed that, they still tend to survive in multiple environmental conditions and remain unaffected. Thus, in this way, they were able to carry out their role in the intestine.

Explanation of Solution

For the determination of changes in bacterial cell that is adapted to different conditions, the scientists placed the bacterial cells in two different solutions: hypertonic and isotonic. In the first solution (hypertonic), the solute concentration was higher than the solute concentration present inside the cell. The second solution was of the same tonicity as that of the bacterial cell.

In the hypertonic solution, the bacterial cells expressed a protein named OmpC in their membranes. This protein was separated by polyacrylamide gel electrophoresis (PAGE) technique. The protein was analyzed with the help of a western blot. In western blot, the darker stain of OmpC extracted from hypertonic solutions represented its high quantity in those cells.

Conclusion

Thus, the gel electrophoresis was used to detect the presence of a protein in the cells. Thus, OmpC is present in higher quantities in the cell membranes in the hypertonic solution as compared to the isotonic or hypotonic solutions. This experiment provided evidence for the changes in the membrane proteins with altering environment.