Question

test content
question 1
what is the purpose of adding a dna ladder to one of the wells during agarose gel electrophoresis?
a to stain the dna fragments and make them visible under uv light
b to provide a visual marker for the starting point of the dna migration
c to enhance the electrical conductivity of the running buffer
d to create a standard for comparing the sizes of unknown dna fragments

Explanation:

A DNA Ladder consists of DNA fragments of known sizes. During agarose gel electrophoresis, when DNA fragments migrate through the gel based on their size (smaller fragments move faster), the DNA Ladder in one well serves as a reference. By comparing the migration distance of unknown DNA fragments (in other wells) to the known - sized fragments in the Ladder, we can estimate the size of the unknown DNA fragments.

• Option A: Staining agents like ethidium bromide are used to stain DNA fragments and make them visible under UV light, not the DNA Ladder.
• Option B: The wells themselves (where the DNA is loaded initially) are the starting point of DNA migration, and the DNA Ladder does not serve as a marker for the starting point.
• Option C: The running buffer (e.g., TAE or TBE buffer) provides the ions for electrical conductivity, and the DNA Ladder has no role in enhancing the electrical conductivity of the running buffer.

Answer:

D. To create a standard for comparing the sizes of unknown DNA fragments