Chapter 16; Biology - Gene Regulation
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Introduction:
● Organisms have a lot of genes
● These genes are not all expressed at the same time
● These genes have on and off switches at several levels to affect the
activities of the cells
● This is called gene regulation: here are different process in which it
occurs
○ Transcription
○ Post-transcriptional regulation
○ Translation
○ Post-translational regulation
Gene regulation in prokaryotes:
Example of E. Coli:
● Let’s start with an example for gene regulation in prokaryotes: let’s use the
bacteria and its genes needed to use sugar as an energy source. Any
sugar may work for their energy; lactose or glucose.
● Three enzymes are needed by this bacteria to use lactose as an energy
source (these help catabolize lactose):
○ B-galactosidase
○ Permease
○ Transacetylase
● These enzymes are not needed if there is no lactose available. (If there is
no lactose there is no need to catabolize it).
● This is an example of an inducible operon.
● E. Coli lac operon image:
Slide 7, This is an example of the E. Coli lac Operon:
,Slide 8, inducible E. Coli lac operon with an ABSENCE OF LACTOSE:
● When there is no lactose in the medium of the cell, genes are not
transcribed.
● The failed beginning of transcription in this inducible lac operon without
lactose: the lac operon can’t be transcribed.
○ The active Lac repressor from the lacI gene binds to the operator.
○ The Lac repressor blocks the RNA polymerase from binding to the
operator.
○ Thus, if binding of RNA polymerase to the operator sequence in a
gene does not occur, the transcription process cannot go on without
RNA polymerase.
○ HOWEVER, The repressor occasionally falls off the operator, thus
allowing the RNA polymerase to bind and so transcription can occur.
BUT this transcription will occur at a very low rate. Low rate
transcription will make a few proteins.
, Slide 10, inducible E. Coli lac operon with an PRESENCE OF LACTOSE:
● When there is lactose in the medium in the cell, the genes are transcribed.
● The successful transcription of this inducible lac operon, with lactose:
○ Since there IS lactose around, the permease already present
transports the lactose into the cell.
○ B-Galactosidase, also already present, will convert some of the
lactose into allolactose (this is an inducer).
○ Now this allolactose will bind to the lac repressor, and it will
inactivate it! (inactive repressor which cannot bind to the operator)
This is why allolactose is an inducer! It induces transcription!
○ Now RNA polymerase can bind to the promoter!
○ And transcription of the lac operon genes can occur!
○ Now, the ribosomes will recognize the ribosome binding site
upstream of each of the three coding sequences on the mRNA,
Legend:
Dark red- Big titles
Blue- headers and topics
Pink words- super important, must understand concepts
Red subtitles- image captions and explanations
Introduction:
● Organisms have a lot of genes
● These genes are not all expressed at the same time
● These genes have on and off switches at several levels to affect the
activities of the cells
● This is called gene regulation: here are different process in which it
occurs
○ Transcription
○ Post-transcriptional regulation
○ Translation
○ Post-translational regulation
Gene regulation in prokaryotes:
Example of E. Coli:
● Let’s start with an example for gene regulation in prokaryotes: let’s use the
bacteria and its genes needed to use sugar as an energy source. Any
sugar may work for their energy; lactose or glucose.
● Three enzymes are needed by this bacteria to use lactose as an energy
source (these help catabolize lactose):
○ B-galactosidase
○ Permease
○ Transacetylase
● These enzymes are not needed if there is no lactose available. (If there is
no lactose there is no need to catabolize it).
● This is an example of an inducible operon.
● E. Coli lac operon image:
Slide 7, This is an example of the E. Coli lac Operon:
,Slide 8, inducible E. Coli lac operon with an ABSENCE OF LACTOSE:
● When there is no lactose in the medium of the cell, genes are not
transcribed.
● The failed beginning of transcription in this inducible lac operon without
lactose: the lac operon can’t be transcribed.
○ The active Lac repressor from the lacI gene binds to the operator.
○ The Lac repressor blocks the RNA polymerase from binding to the
operator.
○ Thus, if binding of RNA polymerase to the operator sequence in a
gene does not occur, the transcription process cannot go on without
RNA polymerase.
○ HOWEVER, The repressor occasionally falls off the operator, thus
allowing the RNA polymerase to bind and so transcription can occur.
BUT this transcription will occur at a very low rate. Low rate
transcription will make a few proteins.
, Slide 10, inducible E. Coli lac operon with an PRESENCE OF LACTOSE:
● When there is lactose in the medium in the cell, the genes are transcribed.
● The successful transcription of this inducible lac operon, with lactose:
○ Since there IS lactose around, the permease already present
transports the lactose into the cell.
○ B-Galactosidase, also already present, will convert some of the
lactose into allolactose (this is an inducer).
○ Now this allolactose will bind to the lac repressor, and it will
inactivate it! (inactive repressor which cannot bind to the operator)
This is why allolactose is an inducer! It induces transcription!
○ Now RNA polymerase can bind to the promoter!
○ And transcription of the lac operon genes can occur!
○ Now, the ribosomes will recognize the ribosome binding site
upstream of each of the three coding sequences on the mRNA,
