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Molecular Biology, 4/e
Robert F. Weaver

Messenger RNA Processing II: Capping and Polyadenylation

Processing of Gene Information: Prokaryotes vs. Eukaryotes

Why is control of gene expression different in eukaryotes than in prokaryotes? Eukaryote gene structure and function differ from prokaryote gene structure and function in several important ways. Eukaryotes generally have many more genes and these genes are spread across multiple chromosomes. Prokaryotes have fewer genes and these genes are all located on one chromosome. Groups of genes producing proteins with related functions are often organized into operons in prokaryotes but not in eukaryotes. Eukaryotes also have mRNA that must have its introns excised and the mRNA transported out of the nucleus to the ribosomes. The greater complexity of the eukaryote genome means that a greater variety and complexity of control mechanisms is necessary. There are also more steps in the transcription and translation process at which control of expression can occur in eukaryotes.

View the animation below, then complete the quiz to test your knowledge of the concept.


Which of the following statements about eukaryotic mRNA is TRUE?
A)a cap is added to their 5' end
B)a poly-A tail is added to their 3' end
C)each usually specifies only a single protein
D)A and B
E)A, B, and C

Splicing joins together
A)two introns.
B)two exons.
C)two polypeptides.
D)a DNA and an RNA molecule.
E)an RNA molecule and a polypeptide.

Which of these events occur as a prokaryotic mRNA is being transcribed?
B)addition of a cap
C)addition of a poly-A tail
D)binding of ribosomes
E)more than one of the above

Processing of eukaryotic mRNA occurs in the cytoplasm prior to translation.

Operons are found in eukaryotes but not in prokaryotes.