Question

Which of the following is a difficulty in getting prokaryotic cells to express eukaryotic genes?
a. The signals that control gene expression are different for prokaryotes, thus requiring prokaryotic promoter regions to be added to the vector.
b. The genetic code differs because prokaryotes substitute the base uracil for thymine.
c. Prokaryotic cells do not recognize eukaryotic stop and start codons.
d. The ribosomes of prokaryotes are not large enough to handle long eukaryotic genes.

Answer 1

Prokaryotic and eukaryotic cells, both have the same genetic code which implies that both substitute the base uracil for thymine while transcribing a gene.

They also have the same start codon, that is AUG and either of the three stop codon those is UAG, UAA, and UGA.

Even though they have a different ribosomal unit in their translation machinery (i.e. in case of prokaryotic, translation unit comprises the 50S and 30S ribosomal unit, while, in case of a eukaryote, it is the 60S and 40S ribosomal unit), they have the same efficiency to translate and therefore does not depends on the length of mRNA. For example, E.coli has rnt gene which encodes enzyme named RNase T (A RNA processing enzyme) has a total of 1538 amino acid in its chain, that means its mRNA length will be 4614nucleotide. Many eukaryotic genes have a mRNA that has less than above-said size.

Therefore, the difficulty in getting prokaryotic cells to express eukaryotic gene is the signals that control gene expression are different for prokaryotes and hence in order to express a eukaryotic gene in the prokaryotic system, the vector containing the eukaryotic gene, must have a prokaryotic promoter region