Question

QUESTION 4 Which of the following is NOT a mechanisms of protein expression? Specific transcription factors binding to enhancers Export of mRNA into the cytoplasm DNA polymerase phosphorylation 5'UTR secondary structure blocking AUG QUESTION 5 Suppose you have all the necessary proteins for transcription of a gene present AND active/turned on AND in the right location within the cell. Under what conditions would you NOT see transcription of that gene? UmRNA has already been transcribed from that gene but has not left the nucleus yet The gene is packaged into heterochromatin The promoter is blocked by a nucleosome The gene is packaged into euchromatin The gene has a mutation in the coding region QUESTION 6

Answer 1

4: DNA polymerase phosphorylation does not constitute a mechanism for protein expression. It regulates DNA replication. Remaining three answers: specific transcription factors binding to enhancers, Export of mRNA to the cytoplasm and 5’ UTR secondary structure blocking AUG- are the different mechanisms by which gene expression is regulated. Protein synthesis machinery is present in the cytoplasm. Therefore, mRNA has to be transported into the cytoplasm in order to make the protein. 5’UTR secondary structure regulates the protein synthesis by regulating the binding of translational machinery to mRNA.

5: Following under two conditions transcription of a gene will not occur.

If a gene is packaged into heterochromatin and promoter is blocked by the nucleosome. Under these two conditions transcription will not occur. Heterochromatin is a transcriptionally inactive, densely packed region, located on the chromosome. A nucleosome is the smallest structural packaging unit of a eukaryotic chromosome which allows the tight packaging of DNA around the histone molecule. In order to access the promoter region and other cis-acting regulatory regions to begin the transcription, nucleosome has to be disassembled and allow the DNA accessibility to RNA polymerase, transcription factor or any other trans-acting elements.