L 20 Flashcards
(32 cards)
ribosomes are rich in what amino acids?
lys and arg with globular domains exposed and extended segments buried
What are the small subunit roles of ribsomes?
recognition of mRNA and tRNA
What are the large subuntion roles of ribosomes.
tRNA recognition
catalyzing polypeptide elongation
what is a polysome?
mRNA with multiple translating ribsomes
The ribosome has three tRNA binding sites, what are they?
A site- aminoacyl -tRNA
P site - peptidyl tRNA
E site - Exit
what occurs at the A site of tRNA binding sites?
tRNA selection
What occurs at the P site for tRNA binding sites?
peptidyl transfer
what occurs at the E site at tRNA binding sites?
Uncharged tRNA exits from E site
Where is the growing polypeptide chain transferred onto in protein synthesis? (it’s one of the arms of tRNA)
incoming aa-tRNA
In e coli postranslational modification results in what?
deformylation of fMet and removal of terminal Met
Brief description of the Shin Dalgarno sequence
This sequence helps recruit the ribosome to the mRNA to initiate protein synthesis by aligning it with the start codon.
Mutations in the Shine-Dalgarno sequence can reduce translation. This reduction is due to a reduced mRNA-ribosome pairing efficiency, as evidenced by the fact that complementary mutations in the anti-Shine-Dalgarno sequence can restore translation.
Initiation step, what does the bacteria use to initiate?
fMet
What do eukaryotes use for initiation step?
Met
What are three steps of protein synthesis - elongation step
- decoding
- transpeptidation
- translocation
There’s no proteins within 18 Angstroms of what active site?
peptidyltransfer active site
What is PTC?
peptidyltransferase center, within large ribosomal subunit
Ribosome’s proof reading mechanism, what is critical for accuracy?
EF-Tu
A slowly hydrolyzed GTP analog increases what for ribosome translation?
GTP analog increases accuracy of translation- expense is lost of speed
How does the antibiotic tetracycline work?
binds to 30s subunit’s A site, blocks entry of aa-tRNA Ef-Tu complex
The N Terminus of growing polypeptide worms through exit of what unit?
large ribosome unit
How do you plug the exit tunnel in the large ribosome subunit?
Macrolide antibiotics plugs the exit from inside
How does eukaryotic initiation start?
small subunit scans from 5’ cap until it finds start codon
what does monocistronic? (Eukaryotic mRNAs are considered this)
contain only a single initiation site and encode only one polypeptide
How may more than one polypeptide be yield during eukaryotic initiation?
polyprotein can be cleaved by site specific proteases
