Which of the following is NOT true regarding DNA gel electrophoresis?

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Question analysis: We are asked which statement is NOT true about DNA gel electrophoresis. Each option will be evaluated for accuracy and will be explained in turn.

Option A: The agarose gel acts as a molecular sieve separating DNA fragments based on size. This is true. The gel matrix creates a porous network; smaller fragments pass through more easily than larger ones, effectively separating DNA by size.

Option B: DNA needs to be stained in order to be visualized in the gel. This is true. DNA is colorless under normal conditions, so dyes or stains (e.g., ethidium bromide, SYBR Safe) are required to visualize the fragments under UV or blue-light illumination.

Option C: Fragments of known size are used to measure the size of the sample DNA. This is true. A DNA ladder or size marker with fragments of known lengths is run alongside samples to estimate their sizes by comparison of migration distances.

Option D: Larger DNA fragments will migrate farther than smaller DNA fragments due to their greater negative charge. This statement is NOT true. DNA carries a uniform negative charge per unit length, so migration is primarily influenced by size: smaller fragments migrate faster and farther through the gel matrix, while larger fragments migrate more slowly. The difference in migration is not due to greater charge on larger fragments; in fact, charge scales with length roughly in proportion to the fragment, but mobility in a gel is dominated by size through the sieve effect, making this statement incorrect.

Option E: By passing an electrical current through the gel, DNA fragments move toward the positive end. This is true. DNA is negatively charged; under an applied electric field, it migrates toward the positive electrode (anode).

Summary: Among the options, Option D is the false statement describing migration behavior, while Options A, B, C, and E describe accurate aspects of DNA gel electrophoresis.

BIOL_2004_81774_202509 Homework 4

Which of the following is NOT true regarding DNA gel electrophoresis?

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