Once the repressor has been released, expression
of the lac genes can take place. In order to express the genes they
must first be transcribed and then translated. This section outlines the transcription
and translation of the two genes being illustrated: Z and Y.
Clicking on each of the thumbnail images will bring up a larger, labeled
version of the described scene.
see the Flash movie for the following sequence of images,
Once the repressor has been released, RNA
polymerase can bind to the DNA and begin transcription.
The mRNA that is produced consists of three domains,
complementing the genes on the DNA.
Each of the three domains on the newly made mRNA corresponds
to a different protein. Only the role of the first two will be studied here.
Now the small and large subunits of the ribosomes can
bind to the mRNA. Here translation of the first protein, ß-galactosidase,
Now both ß-galactosidase (orange) and the second
protein, permease (yellow), are being translated. It should be
noted that in prokaryotic cells more than one ribosome may be attached to
the mRNA at the same time.
After being successfully translated, permease becomes
embedded in the membrane of the cell.