Textbook Question
What observations are consistent with the conclusion that DNA serves as the genetic material in eukaryotes? List and discuss them.
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7. DNA and Chromosome Structure
DNA as the Genetic Material
2:13 minutesProblem 20
Textbook Question
How is the absorption of ultraviolet light by DNA and RNA important in the analysis of nucleic acids?
Verified step by step guidance1
Understand that DNA and RNA absorb ultraviolet (UV) light due to the presence of nitrogenous bases (adenine, thymine, cytosine, guanine, and uracil). These bases have conjugated double bonds that allow them to absorb UV light, with a peak absorption around 260 nm.
Recognize that the absorption of UV light at 260 nm is used to quantify the concentration of nucleic acids in a solution. This is based on the Beer-Lambert law, which relates absorbance to concentration.
Learn that the purity of nucleic acids can be assessed by measuring the ratio of absorbance at 260 nm to absorbance at 280 nm (A260/A280). A ratio of approximately 1.8 for DNA and 2.0 for RNA indicates high purity, while deviations suggest contamination (e.g., protein contamination).
Understand that UV absorption can also be used to study the structural properties of nucleic acids. For example, the hyperchromic effect refers to the increase in UV absorbance when double-stranded DNA is denatured into single strands, which can be used to determine the melting temperature (Tm) of DNA.
Recognize that UV absorption analysis is a non-destructive and rapid method, making it a widely used technique in molecular biology for analyzing nucleic acids in various experimental contexts.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Absorption of Ultraviolet Light
Nucleic acids, such as DNA and RNA, absorb ultraviolet (UV) light primarily at a wavelength of 260 nm due to the presence of aromatic bases. This property is crucial for quantifying nucleic acids in laboratory settings, as the amount of UV light absorbed correlates with the concentration of nucleic acids in a solution.
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Nucleic Acid Analysis
The analysis of nucleic acids involves various techniques to study their structure, function, and quantity. UV absorption is a fundamental method used in spectrophotometry to assess the purity and concentration of DNA and RNA, which is essential for downstream applications like cloning, sequencing, and PCR.
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Purity Assessment
Assessing the purity of nucleic acids is vital for ensuring reliable experimental results. The ratio of absorbance at 260 nm to 280 nm (A260/A280) is commonly used to evaluate contamination by proteins or other substances, with a ratio of ~1.8 indicating pure DNA and ~2.0 for pure RNA, thus guiding researchers in their experimental preparations.
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