MICR - Week 3 Flashcards
(45 cards)
What species of bacteria is used to make recombinant insulin?
E.coli
Describe pathogenesis in terms of translation/transcription
Certain proteins are needed to colonize the host, but if not in host don’t need them so don’t prescribe them
Will sense things like:
- temp
- nutrients
- immune system
Then make things like:
- to attach to cell (pili)
- to evade the immune sys
- to kill host cell
A promotor region is part of
transcription
A promoter and terminator sequence are used in transcription, where are they located?
Promoter = 5’ end
Terminator = 3’ end
Define: operon
Operon: multiple genes that share a promoter
What does the transcription of the operon make?
Transcription of the operon makes polycistronic mRNA
Transcription has 3 stages - describe
Initiation:
1) Sigma factor helps RNA pol recognize promoter
2) RNA pol binds DNA between -35 and -10 region forming a closed complex
3) RNA pol unwinds DNA forming an open complex
4) RNA synthesis begins and sigma factor falls off
Elongation:
1) NTPs are added to 3’ end of RNA-DNA hybrid
2) DNA is rewound as RNA pol progresses
Termination:
There are 2 ways:
= Factor dependent termination
- Rho factor separate RNA-DNA hybrd
= Intrinsic terminators
- inverted repeats for a hairpin/stem loop, with a poly U tail
- the U A bond is weak, so RNA/DNA dissociates and R pol falls off
Define: constitutive genes
Constitutive genes = genes that are always transcribed
Name 2 ways transcription can be regulated (general)
1) DNA binding proteins (initiation)
2) mRNA structure (elongation, termination)
How does bacteria regulate initiation
Sigma Factors - Regulate Initiation
- bacteria uses multiple promoters, and RnaP requires a sigma factor to bind
- diff sigma factors bind diff promoters
- Thus sigma factors control which genes are transcribed, and a change in the level of sigma factors present change the level of transcription
Regulating Initiation - Repressors
Describe
- repressor proteins block initiation
- when a repressor binds, rna p can’t transcribe the gene
- repressors bind the operator region, if a ligand binds them it causes a conformational changing its shape so it can’t bind
- is under negative transcriptional control
Negative Control of Inducible Genes
- Describe
- some repressor controlled genes are inducible
Inducible: repressor binding to operator turns off transcription - Induce ligand stops repressor from binding to operator, turns transcription on
When a ligand binds a repressor, does it turn on or off transcription?
It turns on transcription
When a co-repressor binds a repressor, does it turn on or off transcription?
Co-repressors = a ligand that helps repressors bind DNA
Thus, turns off transcription
Describe the regulation of the Trp operon
- TrpR = repressor
- Trp = co-repressor
High Trp = don’t need more /trp, so Trp binds TrpR to turn off transcription
Low Trp = since Trp is low, it can’t act as a co-represspr thus the operon is transcribed
What example was used for bifunctional activator/repressor?
AraC
Attenuation - Define
Attenuation: ribosomal stalling, impacts transcription
What causes attenuation?
Low aa abundance causes the ribosome to stall, stalling increases transcription of the operon
Tell me about the leader region?
Leader region: ex. TrpL
Location: between the operator and the structural genes
Purpose: encodes for a leader peptide which has no purpose, is just there for attenuation
If TrpL is not being translated:
- 1 and 2, 3 and 4 base pair
- poly U and hairpin form loop for terminator
- RNA P stops transcribing DNA at the poly U tract
If Trp is low, ribosome stalls at Trp codons:
- blocks 1 and 2 from pairing
- 2 and 3 form an antiterminator
- terminator is not formed
- RNAP transcribes genes after DNA poly T tract
If Trp is high, ribosome translates Trp codons, but stalls at TrpL codon:
- blocks pairing of 2 and 3
- 3 and 4 pair forming terminator
- RNAP does not transcribe genes after poly T tract
Define Riboswitch
Riboswitch: mRNA leader region that can adopt 2 different conformations affecting transcription
What are the 2 conformations of riboswitches
Switch is normally off
- terminator stops at poly T
- can be turned on by metabolite/ligand
- binding promotes formation of anti-terminator, which prevents terminator from forming, thus transcription is not stopped at poly T
Switch is normally on
- transcription does not stop at poly T
- turned off by metabolite
- binding promotes formation of anti-antiterminator
- terminator forms, transcription stops at ply T
What was one of the first antibiotics discovered?
Streptomycin
Streptomycin
What is it effective against:
Streptomycin
What is it effective against: Gram negatives
Define: Aminoglycoside
Aminoglycoside: antibiotic that targets the ribosome
