translation Flashcards
(23 cards)
what is the first step in translation?
amino acid activation
in amino acid activation, how does the amino acid get attached?
the attachment of an amino acid to its specific tRNA is mediated by a group of enzymes known as aminoacyl tRNA synthetases
how many aminoacyl tRNA synthetases are there?
there are 20 aminoacyl tRNA synthetases, one for each amino acid and it is able to bind all the different tRNAs that code for its specific amino acid
what does the aminoacyl tRNA synthetase have?
- an active site, which is specific for one type of amino acid and tRNA molecule with appropriate anticodon
what does the enzyme do?
it catalyses the covalent attachment of the specific amino acid to its tRNA at the amino acid attachment site, resulting in the formation of an aminoacyl-tRNA complex
how is the amino acid joined?
by its carboxyl group to the 3’ OH of the tRNA by a ester bond. (when the tRNA has an amino acid linked to it, it is termed as “charged”
formation of initiator tRNAmet
this is used for the recognition of the start codon AUG –> in euk, initiator tRNA carried methionine
initiation of translation involves
tRNA, rRNA, mRNA and at least 10 initiation factors (proteins)
what happens at the initiation of translation?
- the small ribo subunit binds to the 5’ end of the mRNA and a initiator tRNA, which has the anticodon UAC and carries the amino acid methionine
after the ribo binds?
the small subunit then moves downstream (5’ to 3’) along the mRNA carrying initiator tRNA until it reaches the start codon, AUG which signals the start of translation
after they move till the start codon?
the initiator tRNA then binds with the start codon through H bonding
large ribo subunit will bind
with the help of initiation factors (they are proteins)
after the initiation of translation occurs, it forms
a translation initiation complex
hydrolysis of GTP provides the energy for the assembly of this complex
elongation of translation
- codon recognition
- peptide bond formation
- translocation
what is codon recognition (elongation)
- the anticodon of an incoming aminoacyl tRNA base pairs with the complementary mRNA codon in the “A” site of the large subunit of ribosome (assisted by elongation factors)
- requires hydrolysis of GTP
what is peptide bond formation? (elongation)
- the large ribosomal subunit catalyses a chemical reaction (destroys the covalent bond) that releases methionine from the initiator tRNA at the “P” site and attaches it instead by a peptide bond to the second amino acid which is attached to the aminoacyl-tRNA at the “A” site
what enzyme is inside the large ribo subunit?
peptidyl transferase!! and it catalyses the peptide bond formation as well as the breakdown of the covalent bond
what is translocation (elongation)
- it translocated three more nucleotides along the mRNA molecule/one codon in the 5’ to 3’ direction
- hydrolysis of GTP provides energy for this step
it relocates everything one down!!!
after translocation?
at “A” site –> it receives another aminoacyl-tRNA which has an anticodon complementary to the third codon of the mRNA
- then REPEAT
how to terminate after mRNA is translated?
- continues until a stop codon in the mRNA reaches the “A” site
- a release factor binds directly to the stop codon in the “A” site (does not code for any amino acid)
- this causes the addition of a water molecule instead of an amino acid to the polypeptide chain, hydrolysing the polypeptide chain from the tRNA in the P site
the polypeptide is then formed then
it is then released from the ribosome and then it disassembles into its subunits
what is the stop codon
uag uaa uga
