Chapter 16: Control of Gene Expression in Bacteria Flashcards
structural genes
encode proteins that are used in metabolism or biosynthesis or that play a structural role in the cell
regulatory genes
RNA or proteins that interact with other DNA sequences and affect the transcription or translation of those sequences
constitutive genes
structural genes that encode essential cellular functions; expressed continually and are not regulated
regulatory elements
DNA sequences that are not transcribed; affect the expression of DNA sequences to which they are physically linked
levels of gene regulation
- alteration of DNA or chromatin structure
- transcriptional level
- mRNA processing
- mRNA stability
- translational level
- post-translational modification
alteration of DNA or chromatin structure
can change which sequences are available for transcription and the rate at which sequences are transcribed
- DNA methylation
domains
discrete functional part of regulatory proteins that are responsible for binding to DNA
domain binding process
- only a few AAs of the domain will make contact with the DNA (lysine, asparagine, glutamine, glycine)
- AAs form hydrogen bonds to DNA bases or the sugar phosphate backbone
- many proteins have multiple domains that can bind to other molecules such as other regulatory proteins
dynamic DNA-binding proteins
DNA-binding proteins are never permanently attached; they bind and unbind DNA and other regulatory molecules
- other molecules can compete w DNA binding proteins for regulatory sites on the DNA
motifs
simple structures that can fit into the major groove of the DNA double helix
helix-turn-helix
two alpha helices; found in bacterial regulatory proteins
zinc finger
loop of amino acids with zinc at the base; found in eukaryotic regulatory and other proteins
steroid receptor
two perpendicular alpha helices with zinc surrounded by four cysteines; found in eukaryotic proteins; binds to the DNA backbone as well as the major groove
leucine zipper
helix of leucine and a basic arm; two leucines interdigitate; found in eukaryotic proteins; binds to the two adjacent major grooves
helix-loop-helix
two alpha helices separated by a loop of amino acids
homeodomain
three alpha helices; found in eukaryotic regulatory proteins
operon
a group of bacterial structural genes that are transcribed together along with their promoter and additional sequences that control their transcription
controlling transcription
most important level of gene regulation in bacteria
operon structure
- one end has structural genes that are transcribed into a single mRNA
- transcription is under control of a single promoter which lies upstream of the first structural gene
- RNA polymerase binds to the promoter then moves downstream to transcribe
regulator gene
- helps control the expression of the structural genes of the operon by increasing or decreasing their transcription
- not considered part of the operon
- has its own promoter and is transcribed into a short mRNA, which is translated into a short protein
regulator protein
small protein transcribed by the regulator gene that binds to a region of the operon called the operator and affected whether transcription can take place
operator
DNA sequence in an operon to which a regulator protein binds; this binding affects the rate of transcription of the structural genes
- overlaps the 3’ end of the promoter and sometimes the 5’ end of the first structural gene
negative control
transcriptional control where the regulatory protein is a repressor, binding to DNA and inhibiting transcription
positive control
transcriptional control where the regulatory protein is an activator, stimulating transcription
inducible operons
operons in which transcription is normally off ; something happens to induce transcription or turn it on
repressible operons
operons in which transcription is normally on; something happens to turn it off or repress transcription
negative inducible operons
- encodes an active repressor protein that readily binds to the operator
- the binding of the repressor protein physically blocks the binding of RNA polymerase to the promoter
- for transcription to take place, something must happen to prevent the binding of the repressor to the operator
- transcription is turned on by an inducer binding to the repressor proteins
inducer
small molecule that binds to the repressor, altering its shape and preventing it from binding to DNA, allowing transcription to take place
allosteric proteins
proteins that change shape upon binding to another molecule
negative repressible operons
- always on, needs something to turn it off
- regulator protein is a repressor but it can’t bind to the operator without a corepressor
- typically control proteins that carry out the biosynthesis of molecules needed in the cell
activator
regulatory protein that binds to the DNA (at a site other than the operator) and stimulates transcription
catabolite activator protein (CAP)
site that is about 22 nucleotides long that is located within or slightly upstream of the promoter of lac genes
coordinate induction
simultaneous synthesis of several proteins stimulated by a specific molecule, the inducer
attenuation
transcription begins at the transcription start site, but termination takes place prematurely, before the RNA polymerase even reaches the structural genes
attenuator
secondary structure that forms in the 5’ untranslated region of some operons and causes the premature termination of transcription
- one hairpin produced by the base pairing of regions 1 and 2 and another hairpin produced by the base pairing of regions 3 and 4
- hairpins are followed by a string of uracil nucleotides that stop transcription
antiterminator
protein or DNA sequence that prevents the termination of transcription
- hairpin is formed but there is no string of uracil nucleotides to stop transcription
bacterial enhancers
increase the rate of transcription at genes that are distant from the enhancer
- contain binding sites for proteins
- causes the DNA between the promoter and the enhancer to loop out, so that the transcription activator that is bound to the enhancer can directly interact with the RNA polymerase that is bound to the promoter
antisense RNA
RNA molecules that are complementary to particular sequences on mRNAs
- control gene expression by binding to sequences on mRNA and inhibiting translation
- blocks the ribosome binding site
riboswitches
regulatory sequence in an RNA molecule
- when an inducer binds, this changes the configuration of the RNA molecule and alters the expression of RNA, usually by affecting the termination of transcription or by affecting translation
structural gene mutations
alter amino acid sequence of protein encoded by gene in which mutation occurs
regulator gene mutations
affect transcription of structural genes
operator mutations
affect transcription of structural genes
promoter mutations
affect transcription of structural genes
