Question

If a gene is located in a chromatin region that has high levels of histone acetylation... Select one: a. The gene will have a higher chance of being transcribed as chromatin will be more relaxed (open) b. the gene will be expressed at a higher level because repressors will have a lower chance of binding to the promoter of the gene a c. The gene will be less transcribed because repressors will have a higher chance to bind to the operator of the gene d. The gene will have lower levels of transcription due to the chromatin being highly condensed e. None of the listed statements are appropriate

Answer 1

CORRECT OPTION:

a. The gene will have higher chance of being transcribed as chromatin will be more relaxed (open)

Explanation: High levels of histone acetylation means chromatin is more relaxed and have higher chance of being transcribed. Acetylation of N terminus of lysine residues of histone proteins remove the postive charge on lysine and therefore reduce the affinity between DNA and histone protein. Reduced affinity makes the DNA promoter more accessible to DNA polymerase and transcription factors. So, histone acetylation or genes in high level of histone acetylation will have higher chance of being transcribed.

Note: DNA is negatively charged and lysine is positively charged. So, the positive-negative interaction tighly binds DNA with histone protein.

INCORRECT OPTIONS:

b. the gene will be expressed at higher level because repressors will have a lower chance of binding to the promoter of the gene

Explanation: The concept is that, the gene will be expressed at higher level because promoter is more accesible to DNA polymerase and transcription factors, not because repressor have lower chances of binding to promoter. If gene is more relaxed, then repressor has also higher chances to bind to operator and thus reduced transcription.

c. the gene will be less transcribed because repressor will have higher chances to bind to the operator of the gene

Explanation: Again, as mentioned the gene will be expressed at higher level because promoter is more accesible to DNA polymerase and transcription factors. Although repressor will have higher chances to bind to the operator of the gene, there is a competition in binding of DNA Polymerase - Transcription factors and Repressors to open promoter region. It is seen that histone acetylation increases gene transcription.

d. the gene will have lower levels of trancription due to the chromatin being highly condensed

Explanation: Ruled out by above explanations

e. none of the listed statements are appropriate

Explanation: option a is appropriate

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