How is the size of molecules under analysis measured

(a) By measuring the distance moved through a ruler
(b) By measuring the amount of visualizing dye used
(c) By running a standard molecule whose size is known in parallel
(d) There is no exact criteria for doing so

Correct answer: (C) By running a standard molecule whose size is known in parallel

Explanation:

To determine the size of molecules (e.g., DNA, RNA, or proteins) during electrophoresis, a standard molecular marker (also called a ladder) is run alongside the sample.

• The marker contains fragments of known sizes, allowing for comparison with the unknown sample.
• By comparing the migration distance of the sample with the standard, the size of the unknown molecule can be estimated.

Why Not the Other Options?

• (A) By measuring the distance moved through a ruler ❌

  • Distance alone does not determine size because migration depends on multiple factors, including gel concentration and voltage.
  • A standard ladder is necessary for accurate size determination.

• (B) By measuring the amount of visualizing dye used ❌

  • Dye intensity relates to the amount of sample present, not the size of the molecule.

• (D) There is no exact criteria for doing so ❌

  • There is a standard method—using a molecular weight marker or ladder for comparison.

Final Answer:

✅ (C) By running a standard molecule whose size is known in parallel