7. RNA Flashcards
Steps of transcpxn
1) in proks, RNA pol binds to Pribnow box within promoter region; in euks, RNA Polymerase II finds TATA box within promoter region, unwinds DNA via helicase activity, and makes pre-mRNA aka heterogenous nuclear RNA (hnRNA) via polymerase activity. Transcpxn doesn’t require primers
2) 5’ guanine cap added and 3’ poly A tail added to maximize stability when mRNA leaves nucleus to cytosol for transln
3) Spliceosome composed of snRNA and snRNPs splices introns out (though sometimes pre-mRNA doesn’t always have introns)
Steps of transln
1) for prok, ribosome binds to Shine Dalgarno seq; for euk, tRNA+met binds to small ribosomal unit —> small ribosome unit binds to 5’ cap of mRNA or Kozak seq —> ribosome scans along mRNA till it reaches start codon, then tRNA+met sticks in P site —> large ribosomal unit binds to mRNA
2) ribosome moves in 5’ to 3’ direction and starts adding bases at start codon
3) translation continues till it reaches stop codon. tRNA doesn’t have an anticodon when reaching stop codon; instead, a release factor protein binds and disrupts ribosome/mRNA complex and releases polypeptide
Describe EPA sites
Aminoacyl - tRNA + aa come in
Peptidyl - where peptide builds up
Exit - where free tRNA leaves
What are the three main steps of translation?
Initiation, elongation, termination
What are transcpn factors?
Help look for promoter regions (within 25 bp of start site) and enhancer regions (>25 bp away from start site) in DNA OF EUKS to alter gene expression. No factors in proks. Can dimerize w/ other proteins => heterodimers
What are operons? Pos control vs neg control in gene expression
Inducible or repressible cluster of genes transcribed as single mRNA IN PROKS; no euks!
Presence of activator protein —> turn on gene expression vs gene expression will stay on till a repressor protein turns it off
Where does trancpxn of rRNA take place? What are ribozymes?
Nucleolus. Enzymes made of RNA molec instead of regular proteins
Structural genes vs operator genes vs inducible systems vs repressible systems in prok transcpxn
Contains DNA that code for proteins vs repressor binding site vs needing an inducer to start transcpxn, presence of metabolite —> turn operon on (ex: lac operon) vs needing a corepressor to inhibit transcpxn, presence of metabolite —> turn operon off (ex: trp operon)
Does RNA generally violate Chargaff’s rules?
Nah not for single stranded cuz it doesn’t have complimentary DNA
In euks, mRNA = monocistronic; what does this mean? In proks, mRNA = polycistronic, what does that mean?
Each mRNA translates to only one protein vs each mRNA translates to different proteins
Aminoacyl tRNA synthetase
Transfers aa to respective tRNA, requires ATP
Point vs missense mutation vs frame shift mutation
Misplacing a base vs misplacing aa because of the point mutation vs caused by insertion/deletion of nucleotide, codons not divisible by 3
What are small nuclear RNA (snRNA) and small nuclear ribonucleoproteins (snRNPs)?
Proteins that couple together to make spliceosome, they help recognize splicing sites of introns
Alternative splicing
Splicing different ways from a single hnRNA to create different mRNAs
Examples of post translational modifications
Proper folding by chaperones; carboxylation, prenylation (adding lipid groups to membrane bound enzymes), glycosylation (to shield viruses from immune system), phosphorylation (for rxn coupling or stabilizing enzyme activity), hydroxylation (to oxidize cmpds for detox), acetylation or methylation (to alter gene expression), ubiquitination (add ubiquitous to tag protein for degradation by proteasome); forming quat structure; cleavage of proteins via hydrolysis; forming disulfide bonds for stability
