Chapter 18 Flashcards
Why regulate gene expression?
Able to respond to environment
How do bacteria respond to environmental change?
Regulate transcription
Produce only what they need
Operator
On-off switch
Operon
Entire stretch of DNA that includes the operator, promoter, and genes they control
Repressor
Protein that switches OFF the operon
Bind to operator to block RNA polymerase
STOP polymerase
Activate the operator
What is the repressor a product of?
The regulatory gene
Corepressor
Molecule that cooperates with a repressor protein to switch an operon off
trp uses a…
repressor
so, when lots of trp is present the polymerase will be stopped
Repressible operon
Usually on
Needs REPRESSOR to shut off (stop producing gene)
trp
Inducible operon
Usually off
Needs INDUCER to turn on (start producing gene)
lac
Inducers
Inducers remove repressors so the gene gets shut off
Differential gene expression
the expression of different genes by cells with the same genome
Histone acetylation
Loosens chromatins
Makes them more expressed
short term
only eukaryotes
Histone methylation
Coils chromatins
Makes them less expressed
Long term
only eukaryotes
Epigentic inhertance
DNA sequence not changed
Traits expressed due to acetylation and metyhlation
Only eukaryotes
Control elements
Segments of noncoding DNA that serve as binding sites for transcription factors
Enhancers
distal control elements
far away from promoter
TATA Box
Proximal control element
close to promoter
Activator
Protein that binds to an enhancer and stimulates transcription of a gene
Mediator proteins
Grape like thing that folds the protein once activators are attatched to dismal enhancers
Combinatorial Control of Gene Activity
Particular combination of control elements can activate transcription only where appropriate activator proteins are present
Alternative RNA splicing
Allows many types of proteins from one gene
Repressible operons products
The product of the genes also turns the genes off
Regulatory
Makes repressors to shut itself off
Mutation to the regulatory genes that make repressors not work?
Gene always on
What would happen if you couldn’t bind lactose (lac) to a repressor?
The gene would always be off
If you block the inducer, the repressor would never be removed
What happens when you move the operator?
Whatever is before it is no longer expressed
Where do general transcription factors bind?
TATA box
Enhancers
What is the only thing prokaryotes can do?
Regulate when to turn of or turn off genes
How do you coordinate expression of genes?
Share single common enhancer
The tryptophan operon is a repressible operon that is
turned off when tryptophan is added
What protein is produced by a regulatory gene?
repressor
Lack of corepressor?
Genes are always going to be turned on
A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in
continuous transcription of the structural gene controlled by that regulator.
The lactose operon is likely to be transcribed when
the cyclic AMP and lactose levels are both high within the cell.
Transcription of the structural genes in an inducible operon
starts when the pathway’s substrate is present
For a repressible operon to be transcribed, which of the following must occur?
RNA polymerase must bind to the promoter, and the repressor must be inactiv
In response to chemical signals, prokaryotes can do which of the following?
alter the level of production of various enzymes
There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant?
It cannot bind to the inducer.
Which of the following mechanisms is (are) used to coordinate the expression of multiple, related genes in eukaryotic cells?
Genes are organized into clusters, with local chromatin structures influencing the expression of all the genes at once.
If you were to observe the activity of methylated DNA, you would expect it to
have turned off or slowed down the process of transcription.
Which processes contribute to this dynamic activity?
methylation and phosphorylation of histone tails
Two potential devices that eukaryotic cells use to regulate transcription are
DNA methylation and histone modification.
Steriod hormones bind to
Intracellular receptors
Transcription factors in eukaryotes usually have DNA binding domains as well as other domains that are also specific for binding. In general, which of the following would you expect many of them to be able to bind?
other transcription factors
Gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following?
exons alternative splicing
