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Ch. 10 - DNA Structure and Analysis
Klug - Concepts of Genetics  12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
Chapter 10, Problem 31b

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.

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Step 1: Understand the concept of a hyperchromic shift. In nucleic acids, a hyperchromic shift refers to an increase in UV absorbance at 260 nm when the double-stranded structure denatures into single strands upon heating. This is because single-stranded nucleic acids absorb more UV light than double-stranded forms.
Step 2: Recognize that the presence of a major hyperchromic shift upon heating suggests that the genetic material has a double-stranded structure that can denature, similar to DNA or double-stranded RNA.
Step 3: Consider the types of nucleic acids that exhibit hyperchromic shifts. Double-stranded DNA and double-stranded RNA both show this property, while single-stranded nucleic acids show less or no hyperchromic shift upon heating.
Step 4: Use the information about the hyperchromic shift to infer the nature of the nucleic acid. Since the primitive eukaryote's genetic material shows a major hyperchromic shift, it likely contains a double-stranded nucleic acid.
Step 5: To further characterize the nucleic acid, additional experiments such as enzymatic digestion, base composition analysis, or molecular weight determination could be performed to distinguish between DNA and RNA or identify any unique features.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hyperchromic Shift

A hyperchromic shift refers to an increase in UV absorption at 260 nm when nucleic acids denature, indicating strand separation. This phenomenon is commonly used to study the melting behavior of DNA or RNA, as single strands absorb more UV light than double-stranded forms.
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Nucleic Acid Structure and Types

Nucleic acids, primarily DNA and RNA, differ in structure and function. DNA is typically double-stranded with deoxyribose sugar, while RNA is usually single-stranded with ribose. Understanding these differences helps interpret unusual genetic materials in organisms.
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UV Absorption of Nucleic Acids

Nucleic acids absorb UV light maximally at 260 nm due to their aromatic bases. Monitoring UV absorption changes during heating reveals information about nucleic acid stability and conformation, essential for identifying the nature of genetic material.
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Related Practice
Textbook Question

In some organisms, cytosine is methylated at carbon 5 of the pyrimidine ring after it is incorporated into DNA. If a 5-methyl cytosine molecule is then hydrolyzed, what base will be generated?

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Textbook Question

Because of its rapid turnaround time, fluorescent in situ hybridization (FISH) is commonly used in hospitals and laboratories as an aneuploid screen of cells retrieved from amniocentesis and chorionic villus sampling (CVS). Chromosomes 13, 18, 21, X, and Y are typically screened for aneuploidy in this way. Explain how FISH might be accomplished using amniotic or CVS samples and why the above chromosomes have been chosen for screening.

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Textbook Question

A primitive eukaryote was discovered that displayed a unique nucleic acid as its genetic material. Analysis provided the following information:

The general X-ray diffraction pattern is similar to that of DNA, but with somewhat different dimensions and more irregularity.

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Textbook Question

A primitive eukaryote was discovered that displayed a unique nucleic acid as its genetic material. Analysis provided the following information:

Base-composition analysis reveals four bases in the following proportions: Adenine = 8%; Guanine = 37%; Xanthine = 37%; Hypoxanthine = 18%

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Textbook Question

A primitive eukaryote was discovered that displayed a unique nucleic acid as its genetic material. Analysis provided the following information:

About 75 percent of the sugars are deoxyribose, while 25 percent are ribose.

Postulate a model for the structure of this molecule that is consistent with the foregoing observations.

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Textbook Question

Newsdate: March 1, 2030. A unique creature has been discovered during exploration of outer space. Recently, its genetic material has been isolated and analyzed. This material is similar in some ways to DNA in its chemical makeup. It contains in abundance the 4-carbon sugar erythrose and a molar equivalent of phosphate groups. In addition, it contains six nitrogenous bases: adenine (A), guanine (G), thymine (T), cytosine (C), hypoxanthine (H), and xanthine (X). These bases exist in the following relative proportions:

A =T = H and C = G = X

X-ray diffraction studies have established a regularity in the molecule and a constant diameter of about 30 Å. Together, these data have suggested a model for the structure of this molecule.

Propose a general model of this molecule. Describe it briefly.

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