Q.13 Which one of the following statement is incorrect about gel electrophoresis?

1. Proteins or nucleic acid fragments are separated based on their net charges and mass
2. Differential migration of these molecules through agarose gel or polyacrylamide gel, in which small particles move slowly to resolve better
3. Electrical charge that is on DNA molecule help them to move towards the anode
4. Migration of small DNA fragments through gel is quickly

   Incorrect Statement About Gel Electrophoresis: Small Particles Move Slowly

   The incorrect statement is the second one, as small molecules migrate faster through gels, not slower. Gel electrophoresis separates biomolecules based on charge, size, and shape under an electric field.

   Introduction

   The incorrect statement about gel electrophoresis often confuses migration dynamics in agarose or polyacrylamide gels. Mastering principles like charge-driven movement toward the anode and size-based separation is crucial for molecular biology exams. This guide analyzes each statement for clarity.

   Statement Analysis

   Review each option to pinpoint the incorrect statement about gel electrophoresis.

   • Proteins or nucleic acid fragments are separated based on their net charges and mass: Correct. Separation depends on net charge (uniform in SDS-PAGE for proteins or inherent in DNA) and mass/size; larger molecules face more friction in the gel matrix.

   • Differential migration of these molecules through agarose gel or polyacrylamide gel, in which small particles move slowly to resolve better: Incorrect. Small particles (e.g., DNA fragments) move quickly through gel pores, while large ones migrate slowly for better resolution of smaller sizes.

   • Electrical charge that is on DNA molecule help them to move towards the anode: Correct. DNA’s negative phosphate backbone drives migration toward the positive anode in standard setups.

   • Migration of small DNA fragments through gel is quickly: Correct (minor phrasing issue aside). Smaller fragments travel faster due to less resistance, reaching further in the same time.

   Core Principles

   Gel electrophoresis uses an electric field to separate charged molecules in a porous gel.

   Key factors:

   • Charge: DNA (negative) moves to anode (+); proteins coated with SDS become uniformly negative.​

   • Size/Mass: Inverse relation—smaller fragments migrate faster via “biased reptation” model.​

   • Gel Type: Agarose for DNA (100 bp–25 kb); polyacrylamide for proteins/small DNA with finer pores.​

   • Visualization: Bands stained with ethidium bromide or SYBR, imaged under UV.​

   Applications in Biology

   Essential for:

   • DNA sizing post-PCR/restriction digest.

   • Protein analysis via SDS-PAGE.

   • RNA quality checks; avoids RNAse contamination.​

   In exams like GATE, focus on migration inverses: small/fast, large/slow.

   Common Errors

   Overheating causes “smiling” bands (faster center migration); run at low voltage. Ethidium bromide slows DNA slightly but enhances visualization.