168. Given below are two statements one is labelled as Assertion A and the other is labelled as
Reason R:
Assertion A: In size exclusion chromatography, larger proteins elute earlier and smaller proteins
elute later.
Reason R: When matrices like sephadex are used, the partitioning of protein molecules between
liquid and solid phases is a function of protein size.
In the light of the above statements, choose the correct answer from the options given below:
A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true and R is not the correct explanation of A
C. A is true but R is false
D. A is false but R is true

Introduction

Size exclusion chromatography (SEC) is a powerful technique used to separate proteins based on their size. It operates on the principle that larger molecules pass through the column more quickly than smaller molecules due to their limited interaction with the porous matrix. In this article, we will analyze two statements regarding the elution behavior of proteins in size exclusion chromatography and the role of partitioning in protein separation.

Statement Analysis

Assertion A: In size exclusion chromatography, larger proteins elute earlier and smaller proteins elute later.

• This assertion is true. In SEC, the stationary phase (e.g., Sephadex) contains pores that allow small molecules to enter. Larger molecules, unable to enter these pores, bypass them and elute faster. Smaller proteins, on the other hand, enter the pores and take longer to elute because they navigate through the inner matrix, experiencing more resistance.

Reason R: When matrices like Sephadex are used, the partitioning of protein molecules between the liquid and solid phases is a function of protein size.

• This reason is also true. In size exclusion chromatography, the stationary phase matrix like Sephadex consists of porous beads. The protein molecules partition between the mobile phase (liquid) and the solid phase (solid matrix). The size of the proteins determines how much they interact with the pores: smaller proteins have more opportunity to interact and enter the pores, whereas larger proteins are excluded from entering the pores and elute faster.

Conclusion

Both the assertion and the reason are correct, and the reason provides a valid explanation for the behavior described in the assertion.

Thus, the correct answer is:

A. Both A and R are true and R is the correct explanation of A.