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Flashcards in Transcription in Prokaryotes Deck (17)
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Define the transcriptional unit

formed when RNA polymerase binds to the region of the gene called the promoter. Encodes the first nucleotide of RNA at the +1 site.


What is the synthesis capacity of mRNA in a cell?

One third


What percentage is mRNA at equilibrium in a cell?



What are the four steps of transcription?

1. Promoter recognition
2. Initiation
3. Elongation
4. Termination


What occurs during promoter recognition?

RNA pol. binds to duplex DNA @ promoter and DNA is unwound


What occurs during initiation?

Very short chains of mRNA are synthesized and released, as the RNA pol. tries unsuccessfully to leave the promoter.


What occurs during Elongation?

RNA pol. is finally successful in leaving the promoter, and mRNA synthesis of the strand begins


What occurs during Termination?

synthesis halted when a phosphodiester bond is completed on the last nucleotide. Dissociation


How many types of RNA pol. in prokaryotes?

only one


Is the value of the Delta G for nucleotide addition positive or negative?



What subunits of the RNA pol. contribute to make the Core Enzyme?

- 2 alpha subunits (structural function)
- 1 B-B subunit (contains catalytic center)
- One "w" subunit


The addition of the what factor causes the Core Enzyme to become the holoenzyme?

The sigma factor


What is unique about the holoenzyme?

Unlike the Core Enzyme, the holoenzyme can initiate transcription.
It is also able to increase affinity for the promoter by 100x, while decreasing affinity for all other sequences


What does the binding of the sigma factor to RNA pol. do?

It increases the affinity of RNA pol. to promoters, while decreasing affinity for non-promoter sequences.


What were the three models presented for how RNA pol. finds the promoter? Which one is not valid?

1. Diffusion
2. Exchange
3. Sliding
- sliding is invalid


Explain how the model Diffusion for RNA pol. locating promoter works

RNA pol, in solution, binds to DNA in trial and error process until it finds the promoter (high affinity)


Explain how the model Exchange for RNA pol. locating promoter works

- RNA pol. is already bound to DNA at random
- while still bound to one strand, it runs along an adjacent part of the strand, looking for a region of high affinity (promoter)
- when a promoter is found, it switches off the sequence it was on to the promoter