Multiple Choice
Methods for Analyzing DNA: A source of heat-stable DNA polymerase commonly used in PCR is which of the following organisms?
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18. Molecular Genetic Tools
Methods for Analyzing DNA
Multiple Choice
In agarose gel electrophoresis used for DNA analysis, which DNA fragments move faster through the gel toward the positive electrode?
A
Larger (longer) DNA fragments
B
DNA fragments with higher GC content always move faster than those with lower GC content
C
DNA fragments with more negative charge per nucleotide move faster because charge varies widely among fragments
D
Smaller (shorter) DNA fragments
Verified step by step guidance1
Understand the principle of agarose gel electrophoresis: DNA fragments are negatively charged due to their phosphate backbone and move toward the positive electrode when an electric field is applied.
Recognize that the gel acts as a molecular sieve, where smaller (shorter) DNA fragments can navigate through the pores of the gel matrix more easily than larger (longer) fragments.
Note that the charge-to-mass ratio of DNA fragments is generally constant because each nucleotide contributes approximately the same negative charge, so charge differences do not significantly affect migration speed.
Consider that GC content affects the stability and melting temperature of DNA but does not directly influence the migration speed in agarose gel electrophoresis under standard conditions.
Conclude that the primary factor determining migration speed in agarose gel electrophoresis is fragment size, with smaller fragments moving faster toward the positive electrode.
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