Question

The eukaryotic nucleus contains chromatin, which is a complex of DNA and histone proteins. (1) Explain why histone proteins are rich in lysine and arginine. (2) In the S phase of the cell cycle, how compact would you expect the chromatin structure to be for the parts of the chromosome that codes for histone proteins, and why? (3) Would it be possible for transcription to occur at a high rate during the M phase of the cell cycle? Why or why not? (4) A graduate student discovered that a mutant strain of yeast could not grow on the medium that did not contain the amino acid arginine. Subsequently, the student sequenced the genes responsible for arginine synthesis pathway and discovered that all of the genes were identical to their wild-type counterparts. Describe a chromosomal change that could have given rise to this phenotype.

          The eukaryotic nucleus contains chromatin, which is a complex of
DNA and histone proteins.
(1) Explain why histone proteins are rich in lysine and
arginine. 
(2) In the S phase of the cell cycle, how compact would you
expect the chromatin structure to be for the parts of the
chromosome that codes for histone proteins, and why?
(3) Would it be possible for transcription to occur at a high
rate during the M phase of the cell cycle? Why or why not?
(4) A graduate student discovered that a mutant strain of yeast
could not grow on the medium that did not contain the amino acid
arginine. Subsequently, the student sequenced the genes responsible
for arginine synthesis pathway and discovered that all of the genes
were identical to their wild-type counterparts. Describe a
chromosomal change that could have given rise to this
phenotype.

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Added by Elizabeth H.

Biology for AP Courses

Julianne Zedalis, John Eggebrecht

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Solved by Expert Suman K

05/25/2022

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The positive charge helps the histone proteins bind tightly to the negatively charged DNA, allowing for the coiling and condensation of DNA around the histones. Show more…

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The eukaryotic nucleus contains chromatin, which is a complex of DNA and histone proteins. (1) Explain why histone proteins are rich in lysine and arginine. (2) In the S phase of the cell cycle, how compact would you expect the chromatin structure to be for the parts of the chromosome that codes for histone proteins, and why? (3) Would it be possible for transcription to occur at a high rate during the M phase of the cell cycle? Why or why not? (4) A graduate student discovered that a mutant strain of yeast could not grow on the medium that did not contain the amino acid arginine. Subsequently, the student sequenced the genes responsible for arginine synthesis pathway and discovered that all of the genes were identical to their wild-type counterparts. Describe a chromosomal change that could have given rise to this phenotype.

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00:01 The first question is asking about the region for why the histones are rich in lysine and arginine amino acids.

00:12 Since histone protein has to coil around dna in order to condense the dna.

00:25 And after the process of condensation, the long dna could be easily accommodated inside the nucleus.

00:33 But it has been found that dna contains negative charge.

00:38 It is due to the presence of phosphate groups.

00:44 So in order for tight arrangement of histone proteins around the dna, they should be positively charged.

00:54 And this positive charge to his tone is provided by the positively charged amino acids, that is the lysine and rgv.

01:05 The second question is asking about the organization of chromatin at the s phase of the cell cycle.

01:15 So at the s phase of the cell cycle, since the process of dna replication occurs, as a result of which the organization of chromatin at this stage is loose, or it is decondensed.

01:33 Because in this organization, the genes are exposed.

01:35 Post over which the binding of dna polymerase occurs and as a result of which the genes are being expressed.

01:51 Now these genes undergo the process of transcription because they are also available for the binding of rna polymerase and so results into the production of mrna that codes for histone proteins after the process of translation.

02:11 The third question is asking whether transcription occurs efficiently or not at the m phase of the cell cycle.

02:21 And the answer for this question is no...

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