Multiple Choice
Which of the following DNA sequences is one strand of a restriction enzyme recognition sequence?
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7. DNA and Chromosome Structure
DNA as the Genetic Material
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If cells are grown in a medium containing radioactive 15N, which experimental technique can be used to distinguish newly synthesized DNA from parental DNA after replication?
A
Southern blotting
B
Density gradient centrifugation
C
Gel electrophoresis
D
Polymerase chain reaction (PCR)
Verified step by step guidance1
Understand the principle behind the use of radioactive 15N in DNA replication experiments: 15N is a heavier isotope of nitrogen, so DNA synthesized in the presence of 15N will have a higher density compared to DNA containing the normal 14N isotope.
Recall that the goal is to distinguish newly synthesized DNA (containing 15N) from parental DNA (containing 14N) based on their physical properties, specifically their density.
Consider the experimental techniques listed: Southern blotting detects specific DNA sequences, gel electrophoresis separates DNA by size, and PCR amplifies DNA sequences; none of these separate DNA based on density.
Identify that density gradient centrifugation is a technique that separates molecules based on their density by spinning them at high speeds in a density gradient medium, allowing DNA with different isotopic compositions to form distinct bands.
Conclude that density gradient centrifugation is the appropriate method to distinguish newly synthesized 15N-labeled DNA from parental 14N DNA after replication.
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