In terms of the polycistronic composition of mRNAs and the presence or absence o

Question

In terms of the polycistronic composition of mRNAs and the presence or absence of Shine-Dalgarno sequences, compare and contrast bacterial, archaeal, and eukaryotic mRNAs.

Select the three correct answers.

Bacterial and archaeal mRNAs can be either polycistronic or monocistronic, whereas eukaryotic mRNAs are monocistronic.

Introns are present in eukaryotic and archaeal genes, but are absent from most bacterial genes.

Eukaryotic mRNAs can be either polycistronic or monocistronic, whereas bacterial and archaeal mRNAs are monocistronic.

Some archaeal mRNAs do not contain a 5' UTR and do not contain a Shine-Dalgarno sequence.

Bacterial and archaeal mRNAs that contain a 5' UTR also contain Shine-Dalgarno sequences, whereas eukaryotic sequences do not contain Shine-Dalgarno sequences.

All archaeal and bacterial mRNAs contain a 5' UTR and contain a Shine-Dalgarno sequence.

Explanation / Answer

The three correct answers are

Bacterial and archaeal mRNAs can be either polycistronic or monocistronic, whereas eukaryotic mRNAs are monocistronic.

(Most of the eukaryotic mRNA’s are monocistronic which contains genetic information to translate into one protein chain. But prokaryotes are both poly and monocistronic with many genes forming an operon in prokaryotes called as polycistronic operons.)

Introns are present in eukaryotic and archaeal genes but are absent from most bacterial genes.

(Introns were reported to be present in Archaea in centromere binding factor protein, Watanabe et al 2002; FEBS letters Volume 510, Issues 1–2, 2 January 2002, Pages 27-30).

Bacterial and archaeal mRNAs that contain a 5' UTR also contain Shine-Dalgarno sequences, whereas eukaryotic sequences do not contain Shine-Dalgarno sequences.

Shine Dalgarno sequences are only present in prokaryotes and they are absent in eukaryotes. It’s a consensus sequence which helps to recruit the ribosome to the messenger RNA for initiation of translation. It’s a ribosomal binding site.

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