In eukaryotic cells, the DNA is tightly packed in the form of chromatin. His-tones are positively charged proteins. Negatively charged DNA wraps tightlyaround these proteins to form nucleosomes. Additionally, there are othermechanisms 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 structuralmaintenance of chromosomes?(c) To initiate transcription, compact DNA must partially unwind. Explainthe role of histones in this process.(d) Micrococcal nuclease can cleaves DNA at sites where it can access DNAwithout any specificity of binding to a particular sequence. If chromatin isdigested with this nuclease, even for longer periods, a uniform length of146 bp DNA fragments will be formed. Explain.

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Answered: In eukaryotic cells, the DNA is tightly…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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What is the role of the core histones in compaction ascompared to the role of histone H1?
An old genetic observation is that a normally active gene will be silenced if it is moved by transposition or crossing over from an uncondensed (euchromatic) region to a heavily condensed (heterochromatic) region of a chromosome. Assume the euchromatic chromatin containing the active gene is surrounded by heterochromatic chromatin immediately after insertion. Please explain in terms of the control of histone modification why the normally active gene is silenced when it becomes surrounded by condensed regions. (Do not explain how histone modification causes chromatin condensation.)
A diploid human cell contains approximately 6.4 billion base pairs of DNA. Assuming that the linker DNA encompasses 35 bp, how many nucleosomes are present in such a cell? Use two significant figures. How many histone proteins are complexed with this DNA? use two significant figures.
Explain, How does histone acetylation alter chromatin structure?
The Y chromosome contains large amounts of constitutive heterochromatin. Why might there be more constitutive heterochromatin in the Y chromosome than in other chromosomes?
Many proteins other than histones are found associated with chromosomes. What roles do these nonhistone proteins play? Why do chromosomes have moredifferent types of nonhistone than histone proteins?
The term heterochromatin refers to heavily condensed regions of chromosomes that are largely devoid of genes. Since few genes exist there, these regions almost never decondense for transcription. At what point during the cell cycle would expect to observe decondensation of heterochromatic regions? Why?
Give at least one example of a chromosomal structureor function affected by the following mechanisms formodulating chromatin structure:a. Posttranslational changes of the normal histonesfound in the nucleosome
If histones are acetylated on a lysine amino acid (an epigenomic mark), are genes in this region likely to be expressed or not? Briefly, in a sentence or two, explain your answer. (Hint: In your answer explain what the DNA and chromatin structure would look like in regions with the acetylation compared to regions without).
Let’s suppose you have isolated chromatin from some bizarre eukaryote that has a DNA linker region that is usually 300 to 350 bp in length. The nucleosome structure is the same as in other eukaryotes. If you digested this eukaryotic organism’s chromatin with a high concentration of DNase I, what would be your expected results?
Assuming that the histone octamer forms a cylinder 9 nm in diameter and 5 nm in height and that the human genome forms 32 million nucleosomes, what volume of the nucleus (6 μm in diameter) is occupied by histone octamers?
How many nucleosomes form the “width” of the 300 Angstrom fiber, in chromatin packaging?

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