Translation Flashcards
Stages of translation
- initiation
-elongation
-termination
The code is triplet
3 nucleotides grouped together encodes for a single aminoacide
Overlapping code
A change in one of the base pairs in the DNA would be expected to affect three consecutive codons and therefore three consecutive AA in the corresponding polypeptide
Non-overlapping
Each nucleotide is part of only one coden then only one AA replacement would be expected
Degenerate
Several codons correspond to the same AA
Specific
A single codon can encode only one AA an it is strictly defined which one
Start codons
AUG
Stop codons
-UAG
-UGA
-UAA
Properties of genetic code
-triplet
-Non-overlapping
-degeneratr
-specific
-universal
3 sites of ribosome for association with tRNA
-A(aminoacyl)
-P(peptidly)
-E(exit,
deacylated tRNA released )
Which ribosome for initiation stage
80s ribosome
At initiation stage of translation, what is bound to the P site?
Met-tRNAi
Role of Anticodon of tRNA in contact with small subunit?
Decoding the information contained in the mRNA
Role of AA carrying ends in contact with large ribosomal subunit?
Catalyze peptide bound formation
Special tRNAi
Initiate protein synthesis
Regular tRNAmet
Incorporate met only into a growing protein chain
Reading frame
From a specific start codon to a stop codon
Translation initiation step 1
Bringing the small ribosomal subunit to the initiation codon
In bacterial mRNA, nucleotides before the initiation codon
Shine dalgarno
Shine dalgarno sequence is complementary to what?
Sequence of nucleotides near 3’ end of the 16S ribosomal RNA of small ribosomal subunit
Role of shine dalgarno sequence
Guarantees the recognition and correct localization of initiation codon inside the ribosome
Where does bacterial IF attach?
30s subunit
IF1
-stabilizes attachment of 30s subunit to mRNA
-prevents initiator AA-tRNA from entering the wrong site on the ribosome
IF2
GTP binding protein required for attachment of first AA-tRNA
IF3
-Prevent larger (50s) subunit from joining prematurely to the 30s subunit
-facilitate entry of the appropriate initiator AA-tRNA
Translation initiation step 2
Bringing the first AA-tRNA into the ribosome
Translation initiation step 3
Assembling the complete initiation complex
Initiation step 3
Once the initiator tRNA is bound to the Aug codon and the IF3 is displaced, large subunit (60s) joins the complex and the GTP bound to IF2 is hydrolyzed
Eukaryotes, AUG codon is recognized by what?
Cap structure by action of eIF4E factor
2 complexes that begins initiation in Eukaryotes
-43s complex
-mRNA complex
43s complex
40s subunit bound to several initiation factors and initiator tRNA
mRNA complex
mRNA bound to a separate group initiation factors
Translation elongation step 1
-AA-tRNA selection
-entry of 2nd AA-tRNA into Vacant A site
GTPasr required for Binding of 2nf AA-tRNA to the A site
In bacteria - EF-Tu
-in Eukaryotes - eEF1A
Translation elongation step 2
Peptide bond formation
Translation elongation step 2 is catalyzed by what?
rRNA acting as a ribozyme (peptidyl transferase)
Translation elongation step 3
Translocation
Translocation movement
-di peptidyl-tRNA from A site to P site of the ribosome
- deacylated tRNA from the P site to the E site
GTP bound EFs for translocation
Bacteria
-EF-G
Eukaryotes
-eEF2
Translation elongation step 4
Releasing the deacylated tRNA
RF1
Bacterial, recognizes UAA and UAG stop codons
RF2
Bacterial, recognizes UAA and UGA stop codons
eRF1
Eukaryotes, recognizes all three stop codons
RF3 and eRF3
Release of RF/eRF from ribosomal A site
eRF3 GTP bound
eRF1 to promote cleavage of peptidyl tRNA
final steps in translation
-release of deacylated tRNA from the P site
-dissociation of mRNA from ribosome
-disassembly of ribosome into it’s large nd small subunit
Increase in rate of protein synthesis
-simultaneous translation
-rapid recycling of ribosomal subunits
