A colleague of yours has suggested that nucleosomes are distributed along DNA on

Question

A colleague of yours has suggested that nucleosomes are distributed along DNA only in regions corresponding to protein coding sequences ("genes"). Despite studying for this exam, you're not sure if that's right or wrong. So you do the following: Step 1. Isolate chromatin from a dish full of normal human fibroblasts Step 2. Measure the amount of DNA in your isolated chromatin Step 3. Wash with low salt to remove all the proteins except the core histones Step 4. Extensively digest with micrococcal nuclease (until it won't cut anymore) Step 5. Extract all the proteins from the digested chromatin, including histones. Step 6. Analyze the DNA remaining by gel electrophoresis to detect fragments Step 7. Measure the amount of remaining DNA (fragments, NOT nucleotides) As a control you digest some chromatin after extracting all the proteins. Results of Digestions Based on the results above, and also your knowledge about the information content of the genome, which do you conclude? (circle 1 OR 2): nucleosome distribution is not random but restricted to coding regions nucleosomes are distributed randomly all along chromosomes Justify your answer to A by indicating which of the four results above supports your conclusion and why? What does the control experiment prove? So, just how much DNA did you start within each nucleus, anyway? (in base pairs)

Explanation / Answer

Answer

a).Correct option is number 2

Nucleosome distribution is random all along the chromosome.

b). 75% of DNA was bound to histone and thus, could not be digested by the nucleases. The coding part of DNA in human genome is only 2%. Therefore the results clearly states that the histone binding is not resticted to the coding part.

In control experiment all the DNA was digested, which clearly states that histone binding protect DNA from nuclease action.

c). We started with 200 bp of DNA

Explaination: 75% of remaining DNA is 150 bp. which means total DNA is 150 x 100   = 200 bp

75

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