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In E. coli, the trp operon is on by default, while the lac operon is off. Why do you think that this is the case? 

An unprocessed pre-mRNA has the following structure (5′ to 3′): exon of 50 bp, intron of 110 bp, exon of 70 bp, intron of 20 bp, exon of 130 bp, intron of 75 bp, and exon of 30 bp. Which of the following is not a possible size (in bp) of the mature mRNA?

Which of the following are true of epigenetic changes?

In females, one of the two X chromosomes is inactivated during embryonic development because of epigenetic changes to the chromatin. What impact do you think these changes would have on nucleosome packing? 

Some autoimmune diseases show a positive correlation with dramatically decreased expression of histone deacetylase 9 (HDAC9, an enzyme that removes acetyl groups from histones). Why would the decreased expression of HDAC9 cause immune cells to produce inflammatory genes at inappropriate times?

A scientist identifies a pre-mRNA with the following structure What is the predicted size of the corresponding mature mRNA in base pairs (bp), excluding the 5’ cap and 3’ poly-A tail?

Transcribe and translate the following DNA sequence (nontemplate strand): 5′-ATGGCCGGTTATTAAGCA-3′

Protein synthesis uses a huge amount of a cell’s energy. What trade-offs might exist between efficiency, accuracy, and energy use in this process?

Discuss how degeneracy of the genetic code makes cells more robust to mutations.

Many antibiotics inhibit bacterial protein synthesis. For example, tetracycline blocks the A site on the bacterial ribosome, and chloramphenicol blocks peptidyl transfer. What specific effect would you expect each of these antibiotics to have on protein synthesis?Many antibiotics inhibit bacterial protein synthesis. For example, tetracycline blocks the A site on the bacterial ribosome, and chloramphenicol blocks peptidyl transfer. What specific effect would you expect each of these antibiotics to have on protein synthesis?Tetracycline would directly affect:tRNA binding to the ribosomeribosome assemblygrowth of the protein chainChloramphenicol would directly affecttRNA binding to the ribosomeribosome assemblygrowth of the protein chainTetracycline would directly affect:tRNA binding to the ribosomeribosome assemblygrowth of the protein chainChloramphenicol would directly affecttRNA binding to the ribosomeribosome assemblygrowth of the protein chain