Textbook Question
Describe the transitions that occur as nucleosomes are coiled and folded, ultimately forming a chromatid.
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Ch. 12 - DNA Organization in Chromosomes
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 12, Problem 13
Assume that a viral DNA molecule is a 50-µm-long circular strand with a uniform 20-Å diameter. If this molecule is contained in a viral head that is a 0.08-µm-diameter sphere, will the DNA molecule fit into the viral head, assuming complete flexibility of the molecule? Justify your answer mathematically.
Verified step by step guidance1
Convert all given dimensions to consistent units, preferably micrometers (µm). For example, convert the DNA diameter from angstroms (Å) to micrometers using the conversion factor: 1 Å = 10\textsuperscript{-4} µm.
Calculate the volume of the viral DNA molecule by treating it as a cylinder with length equal to the DNA length and diameter equal to the DNA diameter. Use the formula for the volume of a cylinder: \(V_{DNA} = \pi \times \left(\frac{d}{2}\right)^2 \times L\), where \(d\) is the diameter and \(L\) is the length of the DNA.
Calculate the volume of the viral head, which is a sphere, using the formula: \(V_{head} = \frac{4}{3} \pi \times \left(\frac{D}{2}\right)^3\), where \(D\) is the diameter of the viral head.
Compare the volume of the DNA molecule (\(V_{DNA}\)) with the volume of the viral head (\(V_{head}\)). If \(V_{DNA} \leq V_{head}\), then the DNA can fit inside the viral head assuming complete flexibility; otherwise, it cannot.
Provide a conclusion based on the comparison, justifying mathematically whether the DNA molecule fits inside the viral head.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
DNA Molecular Dimensions and Volume
Understanding the physical size of the DNA molecule involves calculating its volume based on length and diameter. DNA is modeled as a cylinder, so volume is found using the formula π × (radius)^2 × length. Converting units consistently is essential to compare DNA volume with the viral head volume.
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Volume of a Sphere
The viral head is a sphere, and its volume is calculated using the formula (4/3)πr³, where r is the radius. Knowing the viral head's volume allows comparison with the DNA volume to determine if the DNA can physically fit inside.
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Concept of Molecular Flexibility and Packing
Assuming complete flexibility means the DNA can bend and coil without volume change, allowing it to occupy space efficiently. This assumption lets us focus on volume comparison rather than shape constraints, simplifying the problem to whether the DNA volume is less than or equal to the viral head volume.
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Related Practice
Textbook Question
Provide a comprehensive definition of heterochromatin and list as many examples as you can.
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Textbook Question
Mammals contain a diploid genome consisting of at least 10⁹ bp. If this amount of DNA is present as chromatin fibers, where each group of 200 bp of DNA is combined with 9 histones into a nucleosome and each group of 6 nucleosomes is combined into a solenoid, achieving a final packing ratio of 50, determine:
(a) the total number of nucleosomes in all fibers,
(b) the total number of histone molecules combined with DNA in the diploid genome, and
(c) the combined length of all fibers.
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Textbook Question
How many base pairs are in a molecule of phage T2 DNA 52-µm long?
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Textbook Question
Examples of histone modifications are acetylation (by histone acetyltransferase, or HAT), which is often linked to gene activation, and deacetylation (by histone deacetylases, or HDACs), which often leads to gene silencing typical of heterochromatin. Such heterochromatinization is initiated from a nucleation site and spreads bidirectionally until encountering boundaries that delimit the silenced areas. In the brief discussion of position effect, where repositioning of the w⁺ allele in Drosophila by translocation or inversion near heterochromatin produces intermittent w⁺ activity. In the heterozygous state (w⁺/w) a variegated eye is produced, with white and red patches. How might one explain position-effect variegation in terms of histone acetylation and/or deacetylation?
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Textbook Question
Contrast the structure of SINE and LINE DNA sequences. Why are LINEs referred to as retrotransposons?
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