You isolate the human gene for cytochrome C. You also isolate the mRNA for cytoc
ID: 217438 • Letter: Y
Question
You isolate the human gene for cytochrome C. You also isolate the mRNA for cytochrome C. Using reverse transcriptase (from a retrovirus) and the mRNA as template, you make a double standed copy DNA (cDNA) of the mRNA.
You transfer both DNA molecules into a bacterium by inserting them in a circular DNA that can replicate in bacteria (a plasmid.). Suppose both recombinant plasmids are transcribed properly (using the correct strand as template) and the corresponding mRNAs are translated. Which plasmid is most likely to make a functional cytochrome C?
The one with the gene.
The one with the cDNA.
either one but can't predict which.
both are likely to make good cytochrome C.
neither is likely to make good cytochrome C.
The one with the gene.
The one with the cDNA.
either one but can't predict which.
both are likely to make good cytochrome C.
neither is likely to make good cytochrome C.
Explanation / Answer
The plasmid having the double-stranded copy DNA (cDNA) of the cytochrome C RNA is most likely to make a functional cytochrome C. This is beacuse both of the plasmids have been transferred into a bacterium which has no machinery for splicing. Moreover, in bacterium both the transcription and translation is a coupled phenomena. The human gene being from an eukaryotic origin have introns but its mRNA will not contain any part of it. Therefore, when cDNA is prepared from that mRNA there will be no copy of the introns. If the human gene of cytochrome C is inserted in the bacterial host then it will nevertheless transcribe the whole sequence and the mRNA will then have a sequence with the transcribed part of introns. This will not be a functional mRNA copy. On the other hand, as the cDNA will not have any introns, it will make the functional cytochrome C.
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