Lecture 10 - Regulation of bacterial gene expression

Question 1

What are cis-acting sequences?

Answer 1

do not encode for a product e.g. protein, only affect the DNA regions that they are attached to - examples include promoter or terminator

Question 2

What are trans-acting sequences?

Answer 2

encode for products such as proteins - can move away from the site of synthesis and act anywhere on the cell

Question 3

What is a repressor?

Answer 3

protein that binds to sequence on the DNA and prevents the transcription of a certain gene - blocks RNA polymerase from accessing the promoter and transcribing a certain gene

Question 4

What is an operator?

Answer 4

cis sequence on the DNA to which the repressor protein binds

Question 5

What are transcription factors?

Answer 5

proteins that interact with RNA polymerase and assist it with starting transcription

Question 6

Describe negative regulation

Answer 6

In negative regulation, a trans-acting repressor binds to the cis-acting operator to turn off transcription.
Operators are always downstream of promoters. RNA polymerase binds to the promoter and transcribes the gene, mRNA is produced which is then translated into protein. However if a repressor protein binds to the operator RNA polymerase cannot access the promoter and cannot transcribe the gene

Question 7

Describe positive regulation

Answer 7

In positive regulation, trans-acting factors must bind to cis-acting sites in order for RNA polymerase to initiate
transcription at the promoter.
One or several proteins bind to the DNA upstream of the promoter, make physical contact with RNA polymerase and assist it with starting transcription

Question 8

What is an operon?

Answer 8

cluster of two or more genes that are adjacent to one another and transcribed into a single mRNA as a single transcriptional unit
Genes in the same operon usually code for proteins involved in the same metabolic pathway or function - co-regulated because transcription starts from the same promoter