Worked Problems

l. DNA from a eukaryotic gene was isolated, denatured, and hybridized to the mRNA transcribed from the gene; the hybridized structure was then observed with the use of an electron microscope. The following structure was observed.

Intron

(a) How many introns and exons are there in this gene? Explain your answer.

(b) Identify the exons and introns in this hybridized structure.

(a) Each of the loops represents a region where there are sequences in the DNA that do not have corresponding sequences in the RNA; these regions are introns. There are five loops in the hybridized structure; so there must be five introns in the DNA.

Intron

2. Draw a typical bacterial mRNA and the gene from which it was transcribed. Label the 5' and 3' ends of the RNA and DNA molecules, and identify the following regions or sequences:

(a) Promoter (e) Transcription start site

(b) 5' untranslated region (f) Terminator

(c) 3' untranslated region (g) Shine-Dalgarno sequence

(d) Protein-coding sequence

Transcription start Transcription stop

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