Gene Regulation Flashcards
Template strand
complement to RNA; provides the template
Nontemplate strand or the coding strand
the same sequence as RNA (Ts in DNA and Us in RNA); where we find the open reading frame
The Lac Operon is an example of…
an inducible promoter
Will the Lac operon be transcribed in the absence of lactose?
no- the lac operon makes enzymes to break down lactose, so if there is no lactose present the E Coli does not need to break down any lactose; repressor is still bound to operator
Key differences in gene expression in eukaryotes than prokayotes
each gene typically has its own promoter (not organized into operons), chromatin structure affects eukaryotic gene expression (histones), nuclear membrane separates transcription from translation
basal transcription apparatus and transcriptional regulator proteins=
normal transcription (instead of minimal)
regulator proteins or transcription factors can be…
activators or repressors
Activators bind…
enhancers
Repressors bind…
silencers
Gal 4 is a
transcriptional activator protein
regulatory elements that affect the transcription of distant genes
enhancers
The binding of transcription factors to the enhancer causes the DNA…
between the enhancer and the promoter to loop out, bringing the promoter and the enhancer close to each other, so that the transcription factors are able to interact directly with the basal transcritpion apparatus at the core promoter
In the GAL system, galactose is
the inducer
In the GAL system, Gal3 is a…
regulator
In the Gal system, Gal80 is a…
transcriptional repressor protein
What occurs in the Gal system
in the absence of galactose, GAL80 blocks GAL4 from activating transcription; when galactose is present, it binds to GAL3 and changes in conformation of GAL 80 so that GAL4 can interact with basal transcription apparatus and stimulate transcription
DNA sequences that block the effect of enhancers in a position dependent manner
Insulators
If an insulator lies between an enhancer and a promoter,
it blocks the action of the enhancer
How is DNA packaged?
DNA is packaged into nucleosomes forming chromatin
What makes up a nucleosome?
histones and DNA
Chromatin makes DNA less accessible, but it also…
provides many opportunities to regulate gene expression
histone modifications
occur largely at specific residues of histone H3 and H4 N-tails (histone N-tail acetulation, phosphorylation, and methylation of specific lysines)
Lysine Acetylation
associated with actively transcribed DNA (usually stimulates transcription) because they destabilize chromatin structure; acetylated lysines create binding site for specific activators
Chromatin remodeling
catalytic reaction by chromatin remodeling complexes; shifting/removal of nucleosomes results in different DNA becoming accessible (not altering the chemical structures of histones directly)- initates transcription
DNase hypersensitivity sites
associated with active transcription; as genes become transcriptionally active, regions around the genes become highly sensitive to the action of DNase I
DNA methylation
leads to inhibition of transcription; removed before transcription initiation or remain methylated for long-term silencing (attacts DNA deacetylases)
DNA methylation and imprinting
DNA methylation can cause imprinting which is when the expression of an autosomal gene is affected by parental origin (can be expressed in mother, but not in father because paternal allele was methylated)
ICR or the Imprinting Control Region
an insulator that cannot function when methylated
Gene silencing by RNA interference or (RNAi)
post-transcriptional gene regulation
micro-RNA, small-interferring RNA, Piwi-interacting RNA
miRNAs in gene silencing
imperfectly matched to their target RNA sequence; Bind target mRNA 3’UTR: translation inhibition, target RNA for degradation
siRNA in gene silencing
siRNA perflectly matched to their target; target RNA for degradation, target DNA for chromatin remodeling
dicer
cleaves dsRNA, produces short double-stranded fragments
defense against genomic invaders
siRNAs
regulators of endogenous genes
miRNAs
Argonaute proteins
bind small RNA and uses as guides for targeting
