Chapter 15.1: The Elements of Prokaryotic Gene Expression

Question 1

Describe rho independent termination in prokaryotes

Answer 1

• A sequence of bases in the RNA forms a secondary structure, known as a hairpin loop, that serves as a signal for the release of RNA polymerase from the completed RNA

Question 2

How does translation in prokaryotes begin before transcription ends?

Answer 2

 Ribosomes bind to special initiation sites at the 5’ end of the reading frame (the ribosome binding site) while transcription of downstream regions of the RNA is still in progress
o Because prokaryotic mRNAs are often polycistronic (contain several open reading frames for several different proteins), ribosomes can initiate translation at several positions along a single mRNA molecule

Question 3

What is the function of RNA polymerase in transcription of prokaryotes?

Answer 3

o When bound to the promoter, the complete RNA polymerase haloenzyme functions as a complex that both initiates transcription by unwinding the DNA and begins polymerization of bases complementary to the DNA template strand

Question 4

What are the two types of transcription termination signals in prokaryotes?

Answer 4

Rho dependent and Rho independent

Question 5

Why can translation in prokaryotes begin before transcription ends?

Answer 5

o Because no membrane encloses the bacterial chromosome, translation of the RNA message into a polypeptide can begin while mRNA is still being transcribed

Question 6

Describe rho dependent termination in prokaryotes

Answer 6

• A protein factor called Rho recognizes a sequence in the newly transcribed mRNA and terminates transcription by binding to the RNA and pulling it away from the RNA polymerase enzyme

Question 7

What is the key enzyme for transcription in prokaryotes?

Answer 7

RNA polymerase

Question 8

When can regulation of prokaryotic gene expression occur?

Answer 8

o Regulation of prokaryotic gene expression can occur at many different levels

Question 9

What is the function of the sigma subunit in RNA polymerase?

Answer 9

o When bound to the core enzyme, the σ subunit recognizes and binds specific DNA sequences at the promoter

Question 10

What does polycistronic mean?

Answer 10

contain several open reading frames for several different proteins