Study Guide

Where Does it End?

Where Does it End?

And finally…the end…

In prokaryotes, termination is either Rho dependent, or Rho independent. Rho is a specific protein that is thought to bind a specific terminator sequence and promote the disassociation of the RNA from DNA. Other times the new RNA forms a structure that promotes the dissociation of the polymerase from the DNA. This type of dissociation is said to be Rho-independent.
The DNA should be clearly labeled as DNA and the bases should be indicated as inverted repeats. The important thing is to show that the inverted repeats base pair creating a hairpin structure that causes the polymerase to stall. The polymerase should be in the picture, and fall off at the hairpin structure.

What happens in eukaryotes? In eukaryotes, there is a sequence of DNA called the polyadenylation signal sequence. It codes for the sequence AAUAAA on the pre-mRNA. A little while after RNA polymerase II transcribes this sequence, proteins on the newly minted RNA transcript cause the pre-mRNA to fall off the polymerase. 

Those nucleotide bases are probably thinking, “Yippee! Freedom at last!” The poor RNA polymerase doesn’t know what to do though, so it keeps transcribing DNA to RNA. Talk about separation anxiety. An enzyme that moves along the length of the RNA transcript digests it, so there isn’t a ton of extra RNA just floating around aimlessly. Eventually, an enzyme moving along the RNA catches up to the polymerase and causes the polymerase to fall off the DNA, stopping transcription.