Textbook Question
Why is Tₘ related to base composition?
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Ch. 9 - DNA Structure and Analysis
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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Table of contents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Chapter 9, Problem 26
A genetics student was asked to draw the chemical structure of an adenine- and thymine-containing dinucleotide derived from DNA. The answer is shown here:
The student made more than six major errors. One of them is circled, numbered 1, and explained. Find five others. Circle them, number them 2 through 6, and briefly explain each in the manner of the example given.
Verified step by step guidance1
Identify the sugar-phosphate backbone and the bases adenine and thymine in the dinucleotide structure. Recall that DNA nucleotides consist of a deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine or thymine here).
Look for the first error beyond the extra phosphate (already circled as error 1). Check the sugar rings: DNA sugars are deoxyribose, which means the 2' carbon should have a hydrogen (H) instead of a hydroxyl group (OH). If the sugar has an OH at the 2' position, this is an error.
Examine the glycosidic bonds between the sugar and the bases. The bond should be between the 1' carbon of the sugar and the nitrogen atom of the base (N9 for purines like adenine, N1 for pyrimidines like thymine). If the bond is misplaced or missing, mark it as an error.
Check the phosphate linkage between the two nucleotides. The phosphate group should connect the 3' carbon of the first sugar to the 5' carbon of the second sugar. If the phosphate is attached incorrectly (e.g., to the wrong carbon), this is an error.
Inspect the base pairing and hydrogen atoms on the bases. For example, thymine should have a methyl group at the 5 position and proper keto groups. If any atoms are missing or incorrectly placed on the bases, note these as errors.
Verify the overall charge and ionization states of the phosphate groups. Phosphates in DNA are typically negatively charged (O⁻) at physiological pH. If the charges are missing or incorrect, this is an error.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleotide Structure
A nucleotide consists of three components: a nitrogenous base, a five-carbon sugar (deoxyribose in DNA), and a phosphate group. The sugar and phosphate form the backbone, while the base attaches to the sugar's 1' carbon. Understanding the correct bonding and orientation of these parts is essential for identifying structural errors.
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DNA Structure
Phosphodiester Bond Formation
In DNA, nucleotides are linked by phosphodiester bonds between the 3' hydroxyl group of one sugar and the 5' phosphate of the next. This linkage forms the sugar-phosphate backbone. Recognizing the correct number and placement of phosphate groups and their bonds is crucial to avoid errors like extra phosphates or incorrect linkages.
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Base Pairing and Orientation
Adenine (A) pairs with thymine (T) via two hydrogen bonds in DNA. Each base must be attached to the sugar at the correct nitrogen atom (N9 for purines like adenine, N1 for pyrimidines like thymine). Correct orientation and attachment points ensure proper base pairing and molecular stability.
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Related Practice
Textbook Question
What is the chemical basis of molecular hybridization?
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Textbook Question
What did the Watson–Crick model suggest about the replication of DNA?
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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:
A major hyperchromic shift is evident upon heating and monitoring UV absorption at 260 nm.
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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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