Unit 2.5 Lecture 1 Flashcards
Where are genes/proteins regulated?
at each level of Biological Information flow:
- transcriptional
- post-transcriptional
- translational
- post-translational
When do cells regulate gene expression/protein activity?
constantly
What is transcriptional regulation? What does it change?
how frequently a gene is transcribed
- changes how easy it is to recruit RNA polymerase to the promoter
What is translational regulation? What does it change?
how frequently mRNA is translated
- changes the rate mRNA is degraded
- changes the rate of translation by ribosomes
What is post-translational regulation? What does it change?
how frequently a protein functions
- changes protein shape by binding activator or inhibitor proteins
- change protein shape by chemical modification
- changes the rate a protein is degraded
What is regulation of gene expression critical for?
the efficient use of resources and thus survival
Regulation of gene expression varies by gene. What is a constitutively expressed gene?
gene that is expressed all the time because its gene product is needed all the time
(ie. rNA, tRNA, RNA polymerase, ribosomal proteins, amino acyl tRNA synthetases)
Regulation of gene expression varies by gene. What is an environmentally-regulated gene?
gene whose expression level is linked to a condition in the environment, ie. nutrient availability (ie. mal and lac operons)
Regulation of gene expression varies by gene. What is a developmentally-regulated gene?
gene that is expressed only at specific developmental periods of an organism (not discussed in BIOL 112)
How can prokaryotes regular genes?
in clusters called operons
What is an operon?
a set of coding sequences for related proteins, all sharing the same promoter and terminator
it is a cluster of genes encoded on a single mRNA but encoding several proteins
What is an operator?
a region of DNA where a regulatory protein binds, it sometimes overlaps with the promoter
What does transcription of an operon result in?
one long mRNA encoding multiple proteins
What is polycistronic mRNA?
it encodes more than one protein/different polypeptides
Facts about operons. (4)
- each section of the mRNA encoding one polypeptide must have an upstream RBS
- there’s one promoter controlling gene expression of all the genes
- genes are regulated as a cluster
- RNA polymerase transcribes polycistronic mRNA
Describe gene regulation in eukaryotes.
one gene codes one pre-mRNA
Facts about gene regulation in eukaryotes. (4)
- each mRNA encoding one polypeptide has a 5’ cap/5’ UTR for ribosome binding
- promoter controls gene expression by binding transcription factors
- each gene has its own promoter
- RNA polymerase transcribes monocistronic mRNA
What do regulatory proteins in eukaryotes do?
can bind to DNA to activate or repress transcription
Regulatory proteins can bind to DNA to activate or repress transcription. What is positive regulation in eukaryotes?
activator protein binds –> RNA POL binds –> transcription
Regulatory proteins can bind to DNA to activate or repress transcription. What is negative regulation in eukaryotes?
repressor protein binds –> no RNA POL binds –> no transcription
Describe positive transcriptional regulation.
RNA POL can bind to the promoter only if an activator protein binds activator binding site on DNA near promoter
Describe negative transcriptional regulation.
if the repressor protein binds to DNA, it inhibits recruitment of RNA POL and transcription does not occur
What does ‘derepressed’ mean?
if the repressor is not present, the native state of the DNA allows RNA POL complex to be recruited and transcription takes place
How can you differentiate between positive and negative regulation?
whether the regulatory protein binds DNA and prevents or promotes transcription
Describe the differences between positive and negative regulation.
positive: regulatory protein (activator) binds a region by the promoter (operator) and INCREASES transcription (ie. MalT operon)
negative: regulatory protein (repressor) binds to a region by the promoter (operator) and DECREASES transcription (ie. LacI)
Describe the promoters of negatively regulated genes.
they have strong promoters to recruit RNA POL when the repressor is off
weaker promoter: if a gene has an activator, its promoter must not strongly recruit RNA POL on its own
stronger promoter: a gene with a repressor can recruit RNA POL without help, so it’s probably got a stronger protein
How are genes names written?
lower case, and italicized or underlined
How are protein names written?
capitalized first letter and no italics
What are inducers?
signalling molecules that ‘induce’ or trigger operon expression (ie. lactose and maltose)
What do cells import?
lactose, then they break it down for energy
What is lacY?
lactose transporter (permease)
What is lacZ?
cleaves lactose (β-galactosidase)
What are lacY and lacZ proteins encoded by?
lac operon
What do bacteria regulate?
enzymes to break down lactose using the lac operon (lacO)
When is lac operon turned on?
when lactose is present
How does lac operon work?
lac repressor LacI controls the lac operon by binding to the operator region of DNA
What is LacI?
a separate gene upstream of the lac operon that is constitutively expressed
What does lac operon-regulatory protein, LacI, do in low lactose?
binds the operator region of DNA near the promoter region to negatively regulate transcription
lac operon is repressed by LacI but a small amount of transcription (BASAL LEVEL) can occur
What happens when lactose is not present?
no need to make break-down enzymes
What happens when lactose is present?
negative regulation is removed so operon is transcribed
What happens when lactose binds to LacI?
changes its tertiary structure
What happens when LacI is bound to lactose?
- LacI changes shape and cannot bind to the operator
- RNA polymerase can be recruited to the promoter
- lac operon is transcribed at high levels
- LacZ, LacY and LacA proteins are translated
