Multiple Choice
In a standard DNA extraction protocol, what is the primary purpose of adding cold alcohol (ethanol or isopropanol) to the aqueous lysate?
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18. Molecular Genetic Tools
Methods for Analyzing DNA
Multiple Choice
In agarose gel electrophoresis, how are DNA fragments primarily separated?
A
By nucleotide sequence, with AT-rich fragments migrating farther than GC-rich fragments
B
By base composition only, with GC-rich fragments migrating farther due to stronger hydrogen bonding
C
By double-stranded versus single-stranded structure only, with single-stranded DNA always migrating farther regardless of length
D
By fragment size, with smaller DNA fragments migrating farther toward the positive electrode
Verified step by step guidance1
Understand the principle of agarose gel electrophoresis: DNA fragments are separated based on their physical properties as they move through a gel matrix under an electric field.
Recall that DNA molecules are negatively charged due to their phosphate backbone, so they migrate toward the positive electrode during electrophoresis.
Recognize that the gel acts like a molecular sieve, where smaller DNA fragments can move more easily and thus migrate farther through the pores of the gel compared to larger fragments.
Note that while nucleotide sequence and base composition affect DNA properties, they do not primarily determine migration distance in agarose gel electrophoresis; instead, size (length in base pairs) is the key factor.
Conclude that the primary basis for separation in agarose gel electrophoresis is fragment size, with smaller fragments migrating farther toward the positive electrode.
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