module 8 Flashcards
gene regulation
the level of gene expression can vary under different conditions
constitutive
genes that are unregulated
gene regulation is important for cellular processes such as
metabolism, response to environmental stress, cell division
common points of gene regulation in transcription
- gene regulatory proteins bind to the DNA and control the rate of transcription
- formation of a transcriptional terminator ends transcription shortly after it’s begun
common points of gene regulation in translation
- translational repressor proteins can bind to the mRNA
- riboswitches can produce a mRNA conformation
- antisense RNA can bind to the mRNA
Repressors
bind to the DNA and inhibit transcription
common points of gene regulation in posttranslation
- feedback inhibition product inhibits first enzyme in the pathway
- covalent modifications to the structure of a protein
activators
bind to DNA and increase transcription
negative control
transcriptional regulation by repressor proteins
positive control
transcriptional regulation by activator proteins
small effector molecules that increase transcription
bind to activators and cause them to bind to DNA, bind to repressors and prevent them from binding to DNA
genes that are regulated with positive SEMs (inducers) are termed
inducible
small effector molecules that inhibit transcription
corepressors bind to repressors and cause them to bind to DNA
inhibitors bind to activators and prevent them from binding to DNA
genes that are regulated with negative SEMs (compressor) are termed
repressible
repressor protein + inducer molecule =
inducible gene
activator protein + inducer molecule =
inducible gene
repressor protein + corepressor molecule =
repressible gene
activator protein + inhibitor molecule =
repressible gene
enzyme adaption
a particular enzyme appears in the cell only after the cell has been exposed to the enzyme’s substrate
operon
a regulatory unit consisting of a few protein-coding genes under the control of one promoter
polycistronic mRNA
encoded by operon, contains the coding sequence for two or more protein-encoding genes
promoter
binds to RNA polymerase
operator
binds the lac repressor protein
CAP site
binds the Catabolite Activator Protein
Terminator
ends transcription
lacZ
codes b-galactosidase
b-galactosidase
enzymatically cleaves lactose and lactose analogs and converts lactose to allolactose
lacY
codes lactose permease
lactose permease
membrane protein required for transport of lactose and analogs
lacA
codes galactoside transacetylase
galactoside transacetylase
covalently modifies lactose and analogs and prevents toxic buildup of nonmetabolizable lactose analogs
allosteric regulation
allolactose binds to lac repressors and prevents the repressors from binding to the DNA
lacI- mutation
resulted in the constitutive expression of the lac operon even in the absence of lactose
trans-effect
genetic regulation that can occur even though DNA segments are not physically adjacent, mutation complemented by the introduction of a 2nd gene with normal function
cis-effect
a DNA sequence that must be adjacent to the gene(s) it regulates, mutation not affected by the introduction of another normal cis-acting element
catabolite repression
prevents the use of lactose, utilizes cAMP that binds to CAP
diauxic growth
sequential use of two sugars by bacterium
cAMP-CAP complex
increases transcription, in the presence of glucose cAMP is not produced and transcription rate decreases
three operator sites for lac repressor
O1 - next to promoter (downstream)
O2 - downstream from lacZ
O3 - slightly upstream from promoter
lac repressor must bind to two of the three operators to cause repression
O1 and O2 or O1 and O3, can’t do O2 and O3
Riboswitch
transcription continues with an antiterminator stem-loop, transcription ends with a terminator stem-loop, switch in conformation is caused by the binding of the molecule produced from transcribing the mRNA
regulation of gene expression in transcription
- regulatory transcription factors
- arrangement and composition of nucleosomes
- DNA methylation
regulation of gene expression in RNA modification
- alternative splicing
- RNA editing
regulation of gene expression in translation
- protein regulation
- mRNA degradation
- RNA interference
regulation of gene expression in posttranslation
- feedback inhibition
- covalent modification regulate protein function
General transcription factors
required for binding of RNA polymerase
regulatory transcription factors
influence the ability of RNA polymerase to begin transcription of a particular gene
chromatin remodeling complexes change chromatin structure in one of 3 ways
- change in the position of nucleosomes
- eviction of histone octamers
- change in the composition of nucleosomes
histone code
the pattern of modification that provides binding sites for proteins that promote alteration in chromatin structure
de novo methylation
two previously non-methylated strands become methylated
maintenance methylation
recognizes an unmethylated strand that should be methylated (usually after DNA replication of two previously methylated strands)
gene activation steps
- one or more regulatory transcription factors (activators) bind to an enhancer
- the activators recruit coactivators (chromatin remodeling complexes and histone-modifying enzymes)
- RNA polymerase binds to the core promoter to form a preinitiation complex
- RNA polymerase proceeds to the elongation phase and makes an RNA transcript
nucleosome-free region
found at the beginning and end of most eukaryotic genes
Elongation phase of transcription
- formation of an open complex
- promoter escape
- proximal promoter pausing
- histone modification
Chromatin Immunoprecipitation Sequencing
a technique used to map the locations of specific nucleosomes within a genome
