Flashcards in Chapter 18: Regulation of Gene Expression Deck (39)
What is coordinated control?
Having all the genes on or off at the same time in order to control the expression of the gene
What if the genes in the same pathway are not all on or off at the same time?
The gene is ignored
What is an operon?
A series of genes on one piece of DNA that work together
What is an operator?
The on and off switch before the specific DNA sequence
What are the properties of repressible operons?
- Operon is always ON
- Enzymes constantly being made
^RNA polymerase is constantly transcribing mRNA
- An inactive repressor is always produced, and an amino acid needs to activate the repressor in order to bind to the operator and turn it off
What is an example of a repressible operon?
- trp Operon in E. Coli
- Operator is always ON
- A separate gene makes an Inactive Repressor (cannot bind to the operator)
- An amino acid will activate the Inactive Repressor, making it active
- The repressor binds to the operator and turns it off
What are the properties of inducible operons?
- Operon is always OFF
- Enzymes are not being made
^RNA polymerase is not transcribing mRNA
- An active repressor is always produced and is always bonded to the operator.
- An amino acid needs to inactivate the repressor in order to remove it from the operator so that RNA polymerase can transcribe the operon
What is an example of an inducible operon?
- lac Operon in E. Coli
- Operator is always OFF
- A separate gene makes an Active Repressor (always bounded to the operator)
- An amino acid will inactivate the Active Repressor, making it inactive
- The repressor will fall off of the operator and the operator is switched on, allowing RNA polymerase to transcribe mRNA
When tryptophan is abundant, what happens to the trp operon?
A. Genes are expressed because the depressor protein is bound to the operator
B. Genes are expressed because tryptophan removes the depressor protein from the operator
C. Genes are silenced because the repressor protein is in the active state in the presence of tryptophan
D. Genes are silenced because tryptophan binds to the operator
Tryptophan activates the repressor and it binds to the operator, turning it off and silencing the genes.
An E. coli culture is grown in the absence of glucose SO cells are forced to breakdown lactose for energy. Which of the following do you expect to find in these cells?
A. Repressor bound to the operator, genes off
B. Repressor bound to lactose, genes off
C. Repressor bound to the operator, genes on
D. Repressor bound to lactose, genes on
- The lac amino acid binds to the repressor, inactivating it, so that is unbinds from the operator
- The operator is turned on and the genes are translated (lactose is made so that the cells can break it down and use it for energy)
Explain how genes are expressed in eukaryotes?
1) Chromatin modification - DNA is unwound and exposed for transcription
2) Transcription (in the nucleus)
- DNA --> RNA
3) RNA processing
- introns are removed
4) mRNA transcript is transported to the cytoplasm
5) a. Degradation of mRNA (dies)
b. Translation (mRNA --> protein)
6) Protein processing
- maybe sugars are added
7) Transport to cellular destination
- gene expression!
What are histones?
A ball of proteins that DNA tightly wraps around to form chromosomes
(Starter elastic band ball)
When the histone is unacetylated, DNA _______________________.
DNA is tightly wound around it
When this histone is acetylated, DNA _______________________.
DNA is not tightly wound around it
What does it mean if DNA is not tightly wound around a histone?
(What does it mean if the histone is acetylated?)
Genes can be read
Acetylated = genes read
What does it mean if DNA is tightly wound around a histone?
(What does it mean if the histone is unacetylated?)
Genes cannot be read
Unacetylated = genes not read
What is histone acetylation?
The process of which the histone is acetylated, DNA unwinds from the histone, and the genes can be read.
What is DNA methylation?
When methyl is added and the gene turns off
Methylated = _____________?
Genes not read
Unmethylated = _____________?
What is the goal of transcription?
DNA ---> RNA
What is a promoter?
Where enzymes start reading the DNA (in order to transcribe it)
Has a TATA Box and consensus sequences
What are enhancers?
DNA sequences that attract DNA polymerase for transcription (from far away)
- activator proteins bind to enhancer that is upstream of target sequence
- protein bridge folds over so that activator proteins bind to mediator proteins
- activates transcription at promoter
What are activators?
Proteins that bind to enhancers and help attract RNA polymerase to the site
What are silencers?
They bind proteins that bend DNA so that the genes become hidden in the folded segment and are shielded from transcription activation
What are repressors?
Proteins that block RNA polymerase, preventing transcription
What happens when activators bind to enhancers?
The DNA bends and the enhancers bind to mediator proteins which bind to the promoter
RNA polymerase comes over and transcribes the DNA
What are transcription factors?
Proteins that help transcription
What is post-transcriptional regulation?
- Happens when an mRNA has not been made into a protein (because the cell is busy)
- mRNA enters the miRNA-protein complex
- miRNA will fully pair with the mRNA and degrade it, or it will mostly pair with the mRNA and translation will be blocked.