Chapter 16 Control of Gene Expression
Topics to discuss DNA binding proteins Prokaryotic gene regulation –negative inducible: lac operon –negative repressible: trp operon Eukaryotic gene regulation
6 groups of DNA-binding regulatory proteins have been identified
Prokaryotic Gene Regulation
Operons Operons provide coordinate expression
A model operon
Now let’s look at 2 (of four) groups of operons Negative inducible operons Negative repressible operons
INDUCIBLE Negative inducible operon
Turned on
repressor
Now let’s look at 2 specific operons The Lactose operon: negative inducible The Tryptophan operon: negative repressible
Francois Jacob and Jacques Monod 1961 Studied lactose metabolism/operon in prokayotes J. Monod Won the Nobel Prize in 1965
Sources of prokaryotic energy 1. Disaccharide 2. Monosaccharide Lactose Glucose
Sources of prokaryotic energy Monosaccharide Disaccharide Glucose Lactose
Building the lac operon
ZYAOP I Lac Operon and Proposed Arrangement with control I gene Not technically part of the “operon”
Lactose Metabolism Requires Coordination of all these genes!
Negative inducible operon
(assume only lactose is present)
Next: let’s review just the pattern of expression when: When only lactose is present. When only glucose is present. Glucose and lactose are present in the cell
“Why does the presence of glucose influence lactose metabolism? Lac
To answer this question you need to understand this reaction Adenylyl cyclase Cyclic AMP ATP Glucose may inhibit this enzyme catabolite activator protein +
Now put the pieces all together.
How CAP and cAMP affects the promoter
So….Conditions: Only lactose is present
But…Conditions: Only glucose
And Finally….Glucose and Lactose
Summary
Trypthophan Operon 5 genes involved in the synthesis of the amino acid trypthophan
Negative repressible operon
2 shapes to the mRNA When trp is high When trp is low
Ribosome does not stall
Ribosome stalls
Changes in Chromatin structure and eukaryotic gene regulation Histone acetylation DNA methylation RNA silencing
Do eukaryotes show coordinate gene regulation? Yes, the same response element may be found in related genes.
Also remember gene expression through RNA interference!