Lecture 3 Flashcards
protein synthesis goes in what direction
N terminal to C terminal
what is the start codon
AUG (makes met)
AUG/ met turns into what terminal of a protein
N terminal
where will the peptide bond form between two AA
will lose H2O
how long are tRNAs
70-90 nucleotides long
what structure does tRNA have
2D structure resembling a cloverleaf
what is the role of tRNA
- to act as an adaptor
- to bring the correct AA specified by the codon on the mRNA
what does the trident mean here
- the location is “psi”
- this is the most common modification
true/false the anticodon is complementary to the codon
true
true/false the anticodon is the same sequence as the codon
false
what loops are present on the cloverleaf structure of the tRNA
- T loop
- anticodon loop
- D loop
true/false the accuracy of attaching AA to tRNA is very accurate
true
what end is this
3’ end of tRNA
the process of linking an activated AA to a tRNA is also referred to as what
tRNA charging
the energy in this bond is used for what
- to incorporate the NEXT AA to the polypeptide chain
- not the current one
how many aminoacyl-tRNA synthetases are there
- 20
- one for each AA
how many subunits in ribosomes
2 (large and small)
what does the small subunit of a ribosome do
binds the tRNAs and mRNA
what does the large subunit of a ribosome do
- binds the tRNAs
- catalyzes peptide bond formation
rRNAs are ______ (more/less) highly conserved than the ribosomal proteins
more
what does SSu rRNAs stand for
small subunit rRNAs
sequence comparison of SSu rRNAs from diff organisms are commonly used for what
construction of phylogenic trees
how many binding sites are in the ribosome for mRNA
1
how many binding sites are in the ribosome for tRNA
3
how many tRNAs can be bound on the ribosome at the same time
2
the tRNA that is connected to the polypeptide chain is at which site
P site
what are the diff binding sites of the ribosome
EPA
what are the steps included in translation of mRNA
- incoming Aminoacyl-tRNA binds to A-site
- peptide bond forms with the AA in the P site (which is attached to the pre-existing polypeptide chain)
- the large subunit moved over one codon. so now tRNA 3 is at hybrid site EP and tRNA 4 is at hybrid site PA
- basically the tRNAs stay in place, just the EPA binding sites move over one so they aren’t in the spot they were before
- the large and small subunits are aligned anymore so the small shifts over to align with large
- this means the ribosome is “reset”
- now A site is free for a new tRNA
when do tRNAs dissociate from the E-site
- once the small subunit shifts over, resetting the ribosome
- when the tRNA goes from E/P hybrid site to just E
true/false the ribosome picks which AUG is the right to follow the same way in prokaryotes and eukaryotes
- false
- they’re diff mechanisms
how does the ribosome picks which AUG is the right to follow in prokaryotes
- usine shine-dalgarno sequence
- should be about 10 nucleotides upstread of AUG
- the other (wrong) AUGs won’t have them, so the ribosome knows they’re wrong
how does the shine-dalgarno sequene work
its complementary to the 3’ end of the 16s rRNA within the small subunit of the ribosome
what are polycistronic mRNA
contains coding regions for diff proteins
what is an example of polycistronic mRNA
the lac operon
prokaryotic ribosomes assembling directly on AUG codon within interior of mRNA allows for translation of what
polycistronic mRNA
what are added to eukaryotic mRNA post transcription
- 5’ cap
- 3’ polyA tail
how to ribosomes bind to eukaryotic mRNA
- small subunit binds to 5’ cap
- start scanning 5’ to 3’ until they reach the first AUG
- 90% of the time, they start translation at this first AUG
what is the preferred translation start in eukaryotic mRNA
ideally there will be a Kozak sequence surrounding the 1st AUG
what happens in eukaryotic mRNA is a kozak sequence is missing
- “leaking scanning”
- an AUG codon further downstream would be chosen for translation start
where does “ribosome scanning” mechanisms occur
translation initiation in eukaryotes
10% of the nucleotides within tRNA molecules are modified how
by covalent modifications
how does covalent modifications done to nucleotides within tRNA affect it
- promotes intramolecular basepairings
- this stabilizes tRNA structure
- helps tRNAs recognize correct AA and mRNA codon
what is important in wobble basepairing
isonine
what is the difference between uridine and pseudouridine
modified nucleotide (Ψ) found in cellular tRNA (and rRNA, snRNA, snoRNA)
what is the difference between pseudouridine and N1-Methylpesuedouridine
chemically modified pseudouridine in mRNA made for COVID vaccine
what did the 2023 nobel prize in physiology or medicine do
- the use of pseudouridine to stabilize and reduce cellular toxicity of in vitro transcribed mRNA
- tRNA will survive by mRNA won’t, so they found the major difference was in the modification of uridine
why do stop codons stop
- cause it doesn’t have a complementary tRNA or antidocon
- once it reaches there, they bring in water instead of tRNA cause there is no tRNA for it
true/false the genetic code is redundant
true
how many diff tRNAs are needed to recognize the 4 glycine codons
3
how can a tRNA recognize more than one codon
through wobble base pairing
how does wobble base pairing occur
- according to a list, for each nucleotide in the third position of the codon, there are possible different nucleotides that can be there that can still code for the same tRNA
- this happens often with isonine
- the bonds will be weaker than typical base pairs
when does isonine form
the deamination of adenosine
what is needed for the reaction in which two AA are attached to each other (ie, if they’re not there, AA cannot be added and proteins cant be formed)
- 2 AA
- ATP
how are AA attached to tRNA
- ATP hydrolysis happens, producing energy
- AA will be “activated” by attaching its carboxyl group to AMP
- this makes an adenylated AA
- the AMP then switches places kinda with the 3’ end of the tRNA molecule
- the AMP goes away
