DNA mutation and repair- part 2 Flashcards
what direction is the the new DNA template strand made in using RNA polymerase?
5’-3’
what does RNA polymerase I do?
transcribes most rRNA
what does RNA polymerase II do?
transcribes all protein coding genes and some small nuclear RNA
what does RNA polymerase III do?
transcribes tRNA genes, 5’s rRNA and genes for some small structural RNA
what is required for all promoters to help RNA polymerase II?
basal transcription factor
during a bacterial infection the cytokine TNF is produced an present in high conc with 2hrs in the plasma. How can many produced at once?
amplification during transcription and due to the action of polyribosomes
what is amplification?
transcribing many identical mRNA very quickly they can then synthesis several identical proteins
what are 3 environments that can stimulate gene transcription?
inflammation
chemicals
mechanical stress
what are some environments that can stimulate gene transcription?
inflammation chemical insults drugs disease nutritional status mechanical stress
which TF pulls the double helix apart at the start site allowing transcription to begin?
TFIIH
what do gene regulatory proteins do?
they bind to specific DNA sequences they are either enhancers or suppressors
what is a pribnow box?
the repressor binding site on the DNA sequence
what is the pathway for allowing transcription to occur?
molecular signal comes from outside and activates the activator protein that then binds to the specific sequence in the promotor which allows transcription to occur
how does a repressor prevent transcription from occurring?
if a repressor is sat in the repressor region when a signal comes in it knocks the repressor off and transcription will occur
where are enhancers normally found?
in the major groove
can repressors bind to enhancer regions?
yes even though activator proteins bind there too, in order to prevent activators from binding
what do co-activators do?
they bind to activator proteins/TF and induce or enhance gene transcription. They dont bind to DNA they express histone deactylase activity
what is capping?
on the 5’ end when the addition of a guanine with a methyl group making the molecule more stable and protects the molecule from RNases
what is polyadenylation?
at the 3’ end it cleaves and around 250 adenines are added , improves stability to the molecule and also involved in translation initiation. protects from mRNA from degradation from exonuclease
how does splicing occur?
snRNA proteins come together in a spliceosome and cuts out the intron
where does translation take place?
in the cytoplasm and ribosomes
what is the start codon?
methionine (AUG)
what is a codon?
3 base units of the code
what molecule translates mRNA into proteins?
tRNA
what are the 2 important sites on tRNA molecules?
amino acid binding site and anticodon region
why is the anticodon region important?
because it is complementary to the codon on the mRNA and encodes the codon for the amino acid at the top of the tRNA molecule
what is the structure of tRNA?
- around 80 nucleotides long
- clover structure with 4 short segments and its a double helical
what enzyme covalently bond the amino acid to the right tRNA molecule?
aminoacyl tRNA synthetase
what is rRNA?
its produced from DNA template in the nucleolus and it combined with proteins into large and small ribosomal subunits
what are the different binding sites on a ribosome?
E site- exit
P site- peptide
A site- amino acid
rRNA molecules combine with how many proteins to form a complex known as a ribosome?
50 proteins
which subunit catalyses the formation of peptide bonds that link amino acids together?
large subunit
what is the responsibility of the small subunIt on the ribosome?
matching the mRNA to the codon on the tRNA
what are the 3 main stages of translation?
-initiation, elongation and termination
what needs to occur for translation to happen? steps?
- mRNA migrates to rough ER
- associates with the rRNA of a ribosome
- ribosome reads the infor
- ribosome directs various species of tRNA to bring in their specific amino acid fares
- tRNA specified is determined by the code being translated in the mRNA
what happens during elongation?
-new tRNA come and join on their amino acid to growing polypeptide chain
what happens during termination?
due to the stop codon a release factor comes and releases the polypeptide chain
what is a polyribosome?
when there is more than one ribosome at least 80 nucleotides apart working along an mRNA molecule
what are initiation factors?
factors that will bring all the needed components for initiation togther to allow it to occcur
what is needed from the initiator tRNA molecule?
always has UAC anticodon
always carries amino acid methionine
capable of binding to the P site
what does tetracycline do?
it inhibits protein syntheiss in bacteria by blocking binding of aminoacyl tRNA synthase to A site on ribosome
what does chloramphenical do?
its inhibits protein synthesis in bacterial ribosomes by blocking peptidyl transfer by does not affect cytosolic protein synthesis in eukaryotes
what does streptomycin do?
causes mis-reading of genetic code in bacteria
what does erythromycin do?
blocks movement of mRNA through the small ribosomal subunit
what does rifamycin do?
inhibits initiation of RNA chains by binding to RNA polymerase
what is used to encourage protein folding ?
energy and molecular chaperones to prevent mis-folding
what are some post-translational modifications that may occur?
- proteolysis
- glycosylation
- insertion of cofactors
- formation of disulfide bonds
- phosphorylation
what is proteolysis?
removal of signal sequences by hydrolysis of peptide bond and enzyme activation of pro-enzymes
what are signal sequencing ?
when proteins are are directed to a specific site for their function
what is glycosylation?
the process of oligosaccharides covalently linked to amino acids to form glycoproteins.
what determines a proteins turnover (halflife?
its N-terminal residue, some PEST proteins are more rapidly degrade that other proteins
what enzyme is involved in all protein degradion pathways?
protease
what is a non-specific degradation pathway?
where protease called cathepsins are present in lysosomes
what proetin is involved in the ATP-dependant pathway for protein degradation?
ubiquitin
what amino acid doe sthe ubiquitin bind to in the protein it wants to degrade?
a leucine
what needs to happen for ubiqutin to work?
4 or more ubiquitin molecules need to bind - polyubiquinctinated in a chain so the protein can be targeted by proteasomes
