Textbook Question
What is the chemical basis of molecular hybridization?
Ch. 10 - DNA Structure and Analysis
Klug12th EditionConcepts of Genetics ISBN: 9780135564776
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Table of contents
- Ch. 1 - Introduction to Genetics17
- Ch. 2 - Mitosis and Meiosis36
- Ch. 3 - Mendelian Genetics51
- Ch. 4 - Extensions of Mendelian Genetics74
- Ch. 5 - Chromosome Mapping in Eukaryotes51
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages46
- Ch. 7 - Sex Determination and Sex Chromosomes33
- Ch. 8 - Chromosome Mutations: Variation in Number and Arrangement40
- Ch. 9 - Extranuclear Inheritance31
- Ch. 10 - DNA Structure and Analysis43
- Ch. 11 - DNA Replication and Recombination44
- Ch. 12 - DNA Organization in Chromosomes30
- Ch. 13 - The Genetic Code and Transcription54
- Ch. 14 - Translation and Proteins47
- Ch. 15 - Gene Mutation, DNA Repair, and Transposition41
- Ch. 16 - Regulation of Gene Expression in Bacteria29
- Ch. 17 - Transcriptional Regulation in Eukaryotes41
- Ch. 18 - Post-transcriptional Regulation in Eukaryotes33
- Ch. 19 - Epigenetics33
- Ch. 20 - Recombinant DNA Technology44
- Ch. 21 - Genomic Analysis36
- Ch. 22 - Applications of Genetic Engineering and Biotechnology36
- Ch. 23 - Developmental Genetics37
- Ch. 24 - Cancer Genetics34
- Ch. 25 - Quantitative Genetics and Multifactorial Traits54
- Ch. 26 - Population and Evolutionary Genetics45
Chapter 10, Problem 27
Considering the information on B- and Z-DNA and right- and left-handed helices, carefully analyze structures (a) and (b) below and draw conclusions about their helical nature. Which is right-handed and which is left-handed?
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Examine the structural features of B-DNA and Z-DNA. B-DNA is a right-handed helix, characterized by a smooth backbone and consistent major and minor grooves. Z-DNA is a left-handed helix, with a zigzag backbone and alternating purine-pyrimidine sequences.
Identify the handedness of a helix by observing the direction of the twist. A right-handed helix twists clockwise when viewed from the top, while a left-handed helix twists counterclockwise.
Analyze structure (a) and determine the direction of its twist. Look for characteristics such as the smooth or zigzag backbone and the orientation of the grooves to infer whether it is B-DNA or Z-DNA.
Analyze structure (b) using the same criteria. Observe the twist direction and structural features to determine whether it is right-handed or left-handed.
Compare the findings for structures (a) and (b) to conclude which one is right-handed and which one is left-handed, based on the observed characteristics and the definitions of B-DNA and Z-DNA.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
B-DNA and Z-DNA Structures
B-DNA is the most common form of DNA in cells, characterized by a right-handed helix with about 10.5 base pairs per turn. In contrast, Z-DNA is a left-handed helix that forms under certain conditions, such as high salt concentrations or specific sequences. Understanding these structural differences is crucial for analyzing the helical nature of DNA.
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Right-Handed vs. Left-Handed Helices
The terms 'right-handed' and 'left-handed' refer to the direction in which the helix twists. Right-handed helices, like B-DNA, twist clockwise, while left-handed helices, like Z-DNA, twist counterclockwise. This distinction affects the physical properties and biological functions of the DNA.
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Helical Parameters and Analysis
Helical parameters, such as pitch, rise per base pair, and base pair orientation, are essential for determining the handedness of a DNA structure. By analyzing these parameters in the provided structures, one can conclude whether they exhibit right-handed or left-handed helical characteristics, which is vital for understanding their biological roles.
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Related Practice
Textbook Question
What did the Watson–Crick model suggest about the replication of DNA?
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Textbook Question
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.
Textbook Question
One of the most common spontaneous lesions that occurs in DNA under physiological conditions is the hydrolysis of the amino group of cytosine, converting the cytosine to uracil. What would be the effect on DNA structure of a uracil group replacing cytosine?
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?
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.