Lecture 16: Gene Expression Flashcards
Understand that gene expression can be regulated at many different levels • Understand the concept of promoter • Understand that transcriptional regulators are DNA binding proteins that can act as activators or repressors • Understand how the Lac operon is regulated in bacteria • Appreciate the complexity of eukaryotic transcriptional regulation • Understand the definition of enhancers and their roles in transcriptional regulation
what makes cells different?
differential gene expression
what is gene expression
the process by which the information encoded in a DNA sequence is translated into a product that has some effect on a cell or organism
differerent levels of how gene expression can be controlled
prokaryotic transcriptional regulation
prokaryotes served as useful moel systems to understand regulation of gene expression
role of promoters in prokaryotic transcriptional regulation
contains sequences recognized and bound by RNA polymerase
is located upstream of the transcription start site
vary in strength of binding to RNA polymerase
-strong promoters will allow transcription to occur; weark doesn;t allow sequence to bind to promoter, needs transcriotional activators
transcriptional activators vs transcriptional repressors
promoter activity is enhanced by transcriptional activators
promoter activity is inhibited by transcriptional repressors
work in concert to provide highly sensitie transcriptional regulation
bind to specific DNA regulatory elements
transcriptional regulators (Activators and repressors) have DNA binding domains
lac operon
operon = a cluster of bacterial genes that can be transcribed from a single promoter
transcription of the Lac operon genes allow E. coli to utilize lactose when glucose is absent
when do the Lac genes get turned on
E. coli use glucose as an energy source but if there is
no glucose available, they can get it by breaking down
lactose (disaccharide of glucose and galactose).
E. coli wants to express Lac genes only when:
1. lactose is in the medium
2. glucose is not available
how does lac repressor function
lac repressor inhibits transcription when lactose is not present
CAP activator function
CAP activates transcription when glucose is not present
how does the Lac operon get regulated
an activator and a repressor work together to regulate the Lac operon
regulation of eukaryotic transcription
-eukaryotic cells contain three distinct RNA polymerases: I, II, III
-promoter contains a TATA box bound by the TATA Box Binding protein or TBP, which helps recruit general transcription factors
-this results in RNA Pol IIrecruitment at the promoter which opens up the DNA double helix in preparation for transcription
what are enhancers?
regulatory DNA sequences that function to allow the transcription of a given gene
bind activator genes
can be located either upstream or downstream of the gene they regulate
can be located either close to or far away (up to tens of thousands of nucleotides) from the transcription start site
DNA looping + protein-protein interaction function
allows the activators to help RNA polymerase initiate transcription
expression of Shh in the limb is controlled by…
a limb-specific enhancer
Shh regulates anterior-posterior patterning of the limb by acting as a morphogen
a —- change that causes ectopic expression of Shh in the limb results in digit duplication in mouse
- single base pair
testing the function of the Shh limb enhancers in mouse
loss of the limb enhancer for Shh is asosciated with the loss of limb in advanced snakes
