Lectures 6-8 Flashcards
What is the functions of mRNA, tRNA, rRNA, hnRNA, snRNA
mRNA: messenger codes for proteins
tRNA: adaptor between mRNA and amino acids
rRNA: structural component of riboosomes, catalysies protein synthesis
hnRNA: hetegeneous nuclear, intermediate form, premRNA processed to make mRNA
snRNA: small nuclear, needed from mRNA maturation, part of splosomes
miRNA: 22-24 neuclotides, controles gene expansion
Descrive RNA polmerase
does not require a primer, synthesies RNA form DNa in 5’-3’ using rNTPs, uses template to add rNTP, RNA product is identical to the non template strand (sense mRNA) but u plraces T
Describe the initiaiton of trancription in prokaryotes
i. singma factor recognizes and binds to the promoter region, -35 and - 10
ii. trancription ubble opens at -10
iii. a single RNA polyermease (alpha2betabeta’) forming holoenzyme and is positioned at +1 nueclottide A
iv. singma facor in released after 10 nucleotides, RNA pol core continues
Describe termination of trancription in prokaryotes
Rho or Rho-indepdendent mechanisms,
-Rho indepdent uses the formation of RNA hairpin sturcute resulting form the trancription of an invered reapat sequence to sloow the polmerease, which that causes the RNA trancript to disengage from the polmerase through disruptoon of weakly bonded U:T repeat sequences present in the trancription bubble
-Rho dendepdne termination requies the binfn of the rho preotin to a specific sequence near the 3’ end of the RNA followed by its movement towars the polermease cause it to disengage
How is termination differnt in pro then euks
trancription and translation is coupled in pro
Describe the 3 main RNA polermeases in eukaryotes
RNA pol 1: trancribes rRna gnes (5.8s, 18s, 28s), pol 2 trancribes genes encoding mRNA, pol 3 trancribes tRNA encoding gnes and the 5s rRNA genes
Describe the initiaion of trancription in eukaryotes
RNA polermeases cannot initaion themseleves needs
- basal trancription facotrs to assemly at the TATA box,
- and formation of basal initation comples facilitated by bing of proximal promoter elements and enhancer elements
What mRNA modification are made in eukaryotes
7MG cap is enqymatically added and cotranlationall to the 5’ end,
poly A tail in enzymaticall added by endonucleolytic leavage downstream of the polyadenlation singal (AAUAA) followed by the addiation of ~200 AMP by poly(A) polymerase
-in rare situation the mRNA trancript can be edited by the insertion or deletion of specifc nuelcotides using a guide RNA (trypansome mitochondira) or by base modification (C-U eidtiing)
What endonucletic cleavage and ligation splicing mechanisms
- Endonucletic cleavage and ligation, ex. tRNA splicaing iin yeast, enzyme requires endonuclease and ligase acitivty
What is autocatalytic splicing mechanism
- Autocatalyic splicing, ex. rRNA precursosr in Tetrahymena involves a RNA caralyzed mechanism of cutting and joining that removes an intervening sequence, no external energy, intro excised by 2 phosphoester bond transfers,
What is the Spliceosome mediated splicing mechanism
- Spliceosome-medicated, ex. removal of INTRONS in pre-mRNA, 2 step reaction carreiid out by spliosomes producing mature mRNA, spliosomes are composed of 5 snRNPS each containing sppecific snRNa (u1, u2, u3 ,u4, u5 u6), specific snRNps rcognize the 5’ splice site (u1) on the brans point of A resude (u2) and the 3’ splice site of U5, cleavage at the 5’ splice site and joining this intron end to the branch point creates a larait strucutre that is movoved folling cleavage at the 3’ splica site, final step is the joingin of the 5’ exon,
What are there consensus nucleotides sequences at splice junctions
Mechanisms have to be precise to prevent frame shift mutations, mutations affecting splice site regonitions sequences can cause genetic diseases
