Concepts of Genetics (12th Edition)
12th Edition
ISBN: 9780134604718
Author: William S. Klug, Michael R. Cummings, Charlotte A. Spencer, Michael A. Palladino, Darrell Killian
Publisher: PEARSON
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Chapter 12, Problem 12PDQ
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 nucleo-some 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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In eukaryotic cells, the DNA is tightly packed in the form of chromatin. His-
tones are positively charged proteins. Negatively charged DNA wraps tightly
around these proteins to form nucleosomes. Additionally, there are other
mechanisms for the compaction of chromatin.
(a) Which histone(s) are critical for higher-order chromatin structure?
(b) What are the non-histone proteins responsible for structural
maintenance of chromosomes?
(c) To initiate transcription, compact DNA must partially unwind. Explain
the role of histones in this process.
(d) Micrococcal nuclease can cleaves DNA at sites where it can access DNA
without any specificity of binding to a particular sequence. If chromatin is
digested with this nuclease, even for longer periods, a uniform length of
146 bp DNA fragments will be formed. Explain.
The picture below depicts electron micrographs of the major levels of chromatin structure. Match each of the listed conditions with the most likely levels of chromatin structure under that condition.
You have discovered a new species of plant. You isolate chromatin from the plant and examines it with
the electron microscope and see characteristic beads on a string structure. After addition of a small
amount of nuclease, which cleaves the string into individual beads that each contain 280 bp of DNA.
With more digestion a 120-bp fragment of DNA remains attached to a core of histone protein. Analysis
of the histone core reveals histones in the following proportions:
H2A 33.3%
H2B 33.3%
H3 0% [no histone H3 found]
H4 33.3%
Based on these observations, what conclusions can you make about the probable structure of
the nucleosome in the chromatin of this plant?
Be specific in describing the nature of the nucleosome: which histones form the core (),
how many of each are present () and size in bp of core-DNA that envelopes it ().
Chapter 12 Solutions
Concepts of Genetics (12th Edition)
Ch. 12 - In bacteriophages and bacteria, the DNA is almost...Ch. 12 - After salivary gland cells from Drosophila are...Ch. 12 - If a human nucleus is 10 m in diameter, and it...Ch. 12 - Roberts syndrome is a rare inherited disorder...Ch. 12 - Prob. 2CSCh. 12 - Roberts syndrome is a rare inherited disorder...Ch. 12 - HOW DO WE KNOW? In this chapter, we focused on how...Ch. 12 - CONCEPT QUESTION Review the Chapter Concepts list...Ch. 12 - Contrast the size of the single chromosome in...Ch. 12 - Describe the structure of giant polytene...
Ch. 12 - What genetic process is occurring in a puff of a...Ch. 12 - During what genetic process are lampbrush...Ch. 12 - Why might we predict that the organization of...Ch. 12 - Describe the sequence of research findings that...Ch. 12 - Describe the molecular composition and arrangement...Ch. 12 - Describe the transitions that occur as nucleosomes...Ch. 12 - Provide a comprehensive definition of...Ch. 12 - Mammals contain a diploid genome consisting of at...Ch. 12 - Assume that a viral DNA molecule is a 50-m-long...Ch. 12 - How many base pairs are in a molecule of phage T2...Ch. 12 - Examples of histone modifications are acetylation...Ch. 12 - Contrast the structure of SINE and LINE DNA...Ch. 12 - Variable number tandem repeats (VNTRs) are...Ch. 12 - It has been shown that infectious agents such as...Ch. 12 - Cancer can be defined as an abnormal proliferation...Ch. 12 - In a study of Drosophila, two normally active...Ch. 12 - Prob. 21ESPCh. 12 - An article entitled Nucleosome Positioning at the...Ch. 12 - Prob. 23ESPCh. 12 - Following is a diagram of the general structure of...Ch. 12 - Microsatellites are currently exploited as markers...Ch. 12 - At the end of the short arm of human chromosome 16...
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- A previously undiscovered single celled organism was found living at a great depth on the ocean floor. Its nucleus contains only a single, linear chromosome consisting of 7x10^6 nucleotide pairs of DNA coalesced with three types of histone-like proteins. The analysis of individual nucleosomes revealed that each unit contained one copy of each protein and that the short linker DNA had no protein bound to it If the entire chromosome consists of nucleosomes (discounting any linker DNA), how many are there and how many total proteins are needed to form them?arrow_forwardWhat is the diameter of a nucleosome?arrow_forwardHuman Chromosome 22 (48 × 106 nucleotide pairs in length) has about 700 protein-coding genes, which average 19,000 nucleotide pairs in length and contain an average of 5.4 exons, each of which averages 266 nucleotide pairs. What fraction of the average protein-coding gene is converted into mRNA? What fraction of the chromosome do these genes occupy?arrow_forward
- The average human chromosome contains about 1 x 108 bp of DNA.(a) If each base pair has a mass of about 660 daltons and there are about 2 g of protein (histones plus nonhistones) per gram of DNA, how much doessuch a chromosome weigh (in grams)?(b) If the DNA were extended, how long would it be?(c) An actual chromosome is about 5 mm long. What is the approximatecompaction ratio?(d) You have about 4 x 1012 cells in your body. If you have 46 chromosomes in each cell, what is the approximate extended length of all of your DNA? For comparison, the distance from the earth to the sun isabout 1.5 x 108 km.arrow_forwardIf a human nucleus is 10 mm in diameter, and it must hold as much as 2 m of DNA, which is complexed into nucleosomes that during full extension are 11 nm in diameter, what percentage of the volume of the nucleus does the genetic material occupy?arrow_forwardwhat are we looking at in part (b)? Is this an11-nm fiber, a 30-nm fiber, or a 300-nm fiber? Does this DNAcome from a cell during M phase or interphase?arrow_forward
- Describe the packaging of chromosomal DNA by histones with diagrammatic representations. Name the various histone modifications and describe any two among them.arrow_forwardChromatin is differentiated into heterochromatin and euchromatin regions, on the basis of staining behaviour in a typical nucleus. Which of the given statements is/are correct w.r.t. heterochromatin? (A) Lightly stained region (B) Chromatin is densely packed (C) Transcriptionally it is inactive (D) Darkly stained region 1. (A) only 2. (A) and (C) only 3. (A), (B) and (C) 4. (B), (C) and (D)arrow_forwardThe average human chromosome contains about 1 x 108 bp of DNA. (a) If each base pair has a mass of about 660 daltons and there are about 2 g of protein (histones plus nonhistones) per gram of DNA, how much does such a chromosome weigh (in grams)? (b) If the DNA were extended, how long would it be? (c) An actual chromosome is about 5 mm long. What is the approximate compaction ratio? (d) You have about 4x 1012 cells in your body. If you have 46 chromosomes in each cell, what is the approximate extended length of all of your DNA? For comparison, the distance from the earth to the sun is about 1.5x108 km.arrow_forward
- Describe what structural changes convert a chromosomal region that is 300 nm in diameter to one that is 700 nm in diameter.arrow_forwardIn Human chromosome 11 GC content is 42%. What is the percentage of each nucleotide on chromosome 11?arrow_forwardassuming a spacing of approxiametly 200 base pairs per nucleosome, how many molecules of histone H4 are present in one somatic human cell?arrow_forward
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