Lecture 6 bacterial Genome and Replication expression, and regulation 2 Flashcards
Transcription regulation
- nucleoid-associated proteins can either increase or decrease transcription
- genetic regulatory proteins can bind to the DNA and control whether or not transcription begins
- Attenuation: transcription can terminate very early after it has begun due to the formation of a transcriptional terminator
- binding of a metabolite to a riboswitch in mRNA can cause premature termination of transcription
Regulation of Translation
- Secondary structure in 3’ end of mRNA prevents degradation of mRNA
- Translational repressor proteins can the mRNA and prevent translation from starting
- Antisense RNA can bind to mRNA and control whether or not translation begins
- Binding of a metabolite to a riboswitch in mRNA can block translation
Posttranslational regulation
- small molecules can bind (noncovalently) to a protein and affect its function. An example is feedback inhibition, in which the product of a metabolic pathway inhibits the first enzyme in the pathway
- The structure and function of a protein can be altered by covalent changes to the protein. These can be reversible (phosphorylation/dephosphorylation) or irreversible (removal of amino acid residues) these are called post translational modifications
Constitutive genes
housekeeping genes that are expressed continuously
inducible enzymes
levels of the enzymes rise in presence of a small effector molecule called an inducer (ex. Beta-galactosidase)
Repressible enzymes
- enzymes that are responsible for repressing formation
- usually present in biosynthetic pathways
what kind of regulation is Trp operon
negative transcriptional control of repressor genes
Characteristics of regulatory proteins
- have DNA binding domains
- either inhibit transcription (negative control) or promote transcription (negative control)
- Can also have allosteric regulatory site
The lac repressor binds to the ___ and inhibits transcription
lac repressor (LacO)
The binding of ____ to the lac repressor prevents it from binding to the operator (LacO) site
Allolactose
what is the positive control of the lac operon
Regulated by catabolite activator protein (CAP)
Catabolite activator protein regulates in response to
presence or absence of glucose
thus allows for preferential use of glucose
what is the negative control of the lac operon
Lac repressor
What are the 3 structural genes of the lac operon
Lac Z: encodes for beta-galactosidase, lacY: endcodes for lactose permease, LacA encodes galactoside transacetylase
The catabolite activator protein (CAP) is also called
cyclic AMP receptor protein (CRP)
CAP exists in what to forms
- active form when 3’,5’- cycle adenosine monophosphate (cAMP) is bound
- inactive form when free of cAMP
what happens to the lac operon in the presence of lactose and glucose
transcription is inhibited by lack of CAP
What happens to lac operon in presence of lactose but absence of glucose
binding of RNA polymerase to promotor is enhanced by CAP and repressor is inactive
what happens to lac operon in absence of both lactose and glucose
CAP is activated but transcription is blocked due to activated repressor
What happens to the lac operon when glucose is present but there is no lactose
transcription is inhibited by lack of CAP and presence of repressor
CAP activity is modulated by ____
cAMP
Levels of cAMP are controlled by
- adenyl cyclase (converts ATP to cAMP and PPi) by PEP
- adenyl cyclase is active only when little or no glucose is present
- in absence of glucose, CAP is active and promotes transcription of operons used for catabolism of other sugars
Explain the regulation of cAMP
when glucose is available, the phosphate of PEP is transferred to EIIA by way of EI and HPr. EIIA then transfers the phosphate to EIIB, which in turn transfers it to the incoming glucose. When glucose is not available, the phosphate cannot be transferred to EIIB and instead remains on EIIA. EIIA-P activates adenyl cyclase and cAMP is made.
What kind of regulation is the tryptophan operon
negative control of repressible genes
what kind of regulation is the Arabinose (ara) Operon
Transcriptional Control by a protein that acts both positively and negatively
- when arabinose is absent then the operon is closed
- when arabinose is present it can bind to the AraC protein and actually open up the operon increasing transcription
what is the difference between riboswitches in gram positive and gram negative bacteria
in gram positive bacteria they function by transcriptional termination, whereas the riboswitches discovered in Gram-negative bacteria regulate the translation of mRNA (note that effector biding elements at 5’ end alters mRNA leader folding pattern)
Translation is usually regulated by
blocking its initiation
functions of sRNAs and noncoding (ncRNAs)
some have been implicated in the regulation of DNA replication and transcription, while many others regulate at the level of translation (may inhibit or enhance)
What are antisense RNAs
RNAs that are complementary to mRNA and function by base pairing (these are ncRNAs or sRNAs that can inhibit or enhance translation)
regulatory systems that affect many genes and pathways simultaneously
global regulatory systems
Genes or operons controlled by a common regulatory protein
Regulon
Operon network under control of a common global regulatory protein but individual operons are controlled separately by their own regulators
Modulon
what is an example of a Modulon
Catabolite repression