Site MapHelpFeedbackThe Lac Operon
The Lac Operon
(See related pages)

Why are several genes for different products involved in the same pathway located next to one another in the genome? The lac operon contains DNA sequences coding for three enzymes involved in the fermentation of lactose. Once transcription is initiated the mRNA for all three enzymes is transcribed as a unit. If one protein is made then all three are made. This is only possible because the DNA sequences for all three genes are located next to one another. Once RNA polymerase activity is initiated it can transcribe the mRNA for all three. If the three genes were in different locations the transcription of each one would have to be controlled separately.

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





1The lac repressor binds to what site within the lac operon?
A)lacZ
B)lacO
C)lacA
D)lacl
E)lacP


2Which of the following is not part of the lac operon?
A)lacO
B)lacZ
C)lacA
D)lacl
E)lacP


3The lac repressor is inactivated by binding to which of the following?
A)lactose
B)betagalactosidase
C)transcription factors
D)glucose
E)allolactose


4The polycistronic mRNA is transcribed from the lac operon when lactose is present in the cell.
A)True
B)False


5The lac repressor protein is active in the absence of lactose within the cell.
A)True
B)False





To learn more about the book this website supports, please visit its Information Center.
Copyright (c)2012 McGraw-Hill Education .
Any use is subject to the Terms of Use and Privacy Notice | Report Piracy


Molecular BiologyOnline Learning Center

Home > Chapter 7 > The Lac Operon