MARIA - LECTURE 3 Flashcards
what are isoaccepting tRNAs
Isoaccepting tRNAs are different tRNA molecules that carry the same amino acid but have distinct anticodon sequences, allowing them to recognize and bind to different codons on mRNA that specify the same amino acid.
each aminoacyl tRNA synthetase attaches a single AA to one or more tRNA
what is proofreading by AA-tRNA synthetase and why must it be done
proofreading: correcting an inappropriate charging event before that tRNA can donate its amino acid
the ribosome is unable to discriminate between correctly and incorrectly charged tRNAs (bc at the end of the day the AA is chosen through codon anticodon interactions))
what is kinetic proofreading
what is chemical proofreading
how are tRNAs recognised by AA-tRNA synthetase (ARS)
recognised through:
anticodon loop
acceptor stem
-> each tRNA has the ACC 3’ sequence, but the acceptor step is different
structure and characteristics of ribosomes
ribosomes catalyse peptide bond formation (condensation)
no proteins are involved, ribosomes are thus ribozymes
what are polyribosomes
cluster of ribosomes translating the same mRNA transcript
composition of prokaryotic ribosome and rate of translation
composition of eukaryotic ribosome and rate of translation
how /where are the different parts of ribosomes produced?
what is shine dalgarno dependent initation
only in prokaryotes
in the 5’ end, before the start codon there is an AU rich sequence that is complementary to 16S rRNA, and therefore stabilises the ribosome on the mRNA
ribosomes can recognise this sequence to know where to start translation
how does a riboswitch of access of shine dalgarno (SD) signals work
how does shine dalgarno dependent initiation happen
how does shine dalgarno independent initiation happen
how do prokaryotes have a special initiator methionine?
the first residue in bacteria is N-formyl Met
therefore there is a special N-formyl Met tRNA that enters the P site for the first time
N formyl Met is made after the methionine has been added to the tRNA, and is only used to initiate
after the protein is made the formyl is removed, and sometimes a few N-terminal amino acids are also removed
how do eukaryotes have a special way of knowing that the incoming methionine if the initiator one
they have a dedicated initiator tRNA, tRNAi Met
diagram of cap dependent initiation
how do ribosomes make their way from the cap to the AUG codon?
diagram of internal ribosome entry site (IRES) mediated initiation
what sequence do ribosomes look for to find the start codon?
example of a scanning translational pathology
diagram of eukaryotic initiation pathway
preparation of the 43S Pre Initiation Complex (PIC)
how does mRNA activation happen
how does eIF4-E interact with the cap
what is the energetic cost of initiation?
2 molecules of GTP are consumed per eukaryotic initiation event
which subunits sense the AUG context
eIF1A and eIF2
step by step of translation initiation
how are eIF2 and eIF5 recycled
how can eIF2 discriminate between tRNAi Met and tRNA Met (for elongation)?
