Translation Flashcards
Definition translation
A process whereby the genetic information in mRNA is translated into sequence of amino acids to form polypeptide .
Initiation
First , a small ribosomal subunit binds to mRNA . Then the small subunit moves along the mRNA until it reaches the start codon (AUG) . The initiator tRNA base pair with start codon . This initiator tRNA carries amino acid methionine . Initiation factors bring in large ribosomal subunit such that initiator tRNA occupies P site . A site is empty.
Elongation
Amino acid are added one by one to the initial amino acid . Occurs in 3 step . First step is codon recognition . mRNA codon in A site forms hydrogen bonds with the anticodon of an upcoming molecule of tRNA carrying its appropriate amino acid . Second step is peptide bond formation . Formation of peptide bond between polypeptide form P site and newly arrived amino acid in A site . Polypeptide separates from tRNA in P site and binds to amino acid carried by tRNA in A site . Last step is translocation . The ribosome translocates the empty tRNA in P site move to E site and free from ribosome . tRNA in A site translocated to P site , leaving A site empty . mRNA moves along with its bound tRNA’s bringing the next codon to be translated into the A site . The process is repeated until complete polypeptide chain is formed . The mRNA is read in 5’ to 3’ codon by codon . The process is unidirectional .
Translation
Elongation continues until A site reaches one of the 3 stop codon . Stop codons do not code for amino acids instead act as signals to stop translation . No aminoacyl tRNA recognize the stop codon . A release factor binds to the stop codon and hydrolyzes the bond between the polypeptide and its tRNA in the P site . Freeing the polypeptide from the ribosome . mRNA detaches and ribosome separates .
