Tuesday, October 27, 2009

#7 Bacteria and mammalian protein in vitro synthesis

GRE-ST question #29.
When bacteria produce mammalian proteins,
cDNA is used rather than genomic DNA. Which of the following is the best explanation?

(A) It is easier to clone cDNA than genomic DNA of comparable size.
(B) It is easier to clone RNA than DNA.
(C) It is not possible to clone the entire coding region of the gene.
(D) Most eukaryotic genes have introns that cannot be removed in bacteria.
(E) Most eukaryotic gene promoters do not function in bacteria.
Show answer
cDNA – complementary DNA, synthesized from mature mRNA (matrix RNA, protein-coding RNA, which is translated by ribosomes).
Intron – non-coding DNA region, that is transcribed into precursor RNA, but removed during splicing while RNA maturing.
Promoters – DNA regions, that signals begin of protein-coding sequences.

This question is uncovered by Alberts et al. in a tiny piece of text about cDNA libraries. Shortly, they remind that bacteria or yeast can't delete non-sense sequences (cos' their DNA have none of those) which are removed during splicing in mammalian. Hence right answer is D.