Textbook Question
What is the physical state of DNA after it is heated and denatured?
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7. DNA and Chromosome Structure
DNA as the Genetic Material
2:15 minutesProblem 31b
Textbook Question
A primitive eukaryote was discovered that displayed a unique nucleic acid as its genetic material. Analysis provided the following information:
A major hyperchromic shift is evident upon heating and monitoring UV absorption at 260 nm.
Verified step by step guidance1
Understand the concept of a hyperchromic shift: A hyperchromic shift refers to the increase in UV absorption (at 260 nm) when double-stranded nucleic acids (like DNA) are denatured into single strands. This occurs because the bases in single-stranded nucleic acids are more exposed to UV light compared to the stacked bases in double-stranded structures.
Identify the significance of the hyperchromic shift: The observation of a hyperchromic shift suggests that the genetic material in this primitive eukaryote is likely double-stranded, as single-stranded nucleic acids do not exhibit this phenomenon to the same extent.
Relate the hyperchromic shift to the type of nucleic acid: Since the hyperchromic shift is a property of nucleic acids, this indicates that the genetic material is either DNA or RNA. Further analysis would be needed to distinguish between the two.
Consider the role of UV absorption at 260 nm: Both DNA and RNA absorb UV light at 260 nm due to their nitrogenous bases. The increase in absorption upon heating confirms the presence of nucleic acids as the genetic material.
Plan further experiments: To confirm whether the genetic material is DNA or RNA, additional tests such as enzymatic digestion with DNase (specific to DNA) or RNase (specific to RNA) could be performed. This would help determine the exact nature of the nucleic acid.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hyperchromic Effect
The hyperchromic effect refers to the increase in absorbance of UV light by nucleic acids when they are denatured, typically due to the separation of double-stranded DNA into single strands. This phenomenon occurs because the bases become more accessible to UV light, leading to a higher absorbance at 260 nm. It is a critical indicator of nucleic acid stability and can be used to assess the melting temperature of DNA.
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Eukaryotic Genetic Material
Eukaryotic organisms possess complex cellular structures, including a defined nucleus that houses their genetic material, primarily in the form of linear DNA molecules. Unlike prokaryotes, eukaryotic DNA is associated with histone proteins, forming chromatin that regulates gene expression and DNA replication. Understanding the nature of eukaryotic genetic material is essential for studying its replication, transcription, and overall function.
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Nucleic Acid Composition
The composition of nucleic acids, which includes DNA and RNA, is fundamental to understanding their function and behavior. Nucleic acids are made up of nucleotide monomers, each consisting of a sugar, a phosphate group, and a nitrogenous base. The specific sequence and type of these bases (adenine, thymine, cytosine, guanine in DNA; uracil replaces thymine in RNA) determine the genetic information carried and influence the stability and reactivity of the nucleic acid under various conditions.
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