Question

Which of the following is NOT directly associated with translation?

A) Elongation of the polypeptide

B) Formation of peptide bonds

C) Complementary base pairing between codon and anticodon

D) mRNA synthesis at the ribosome

E) Transfer of amino acids by tRNAs

Answer 1

ANS. OPTION D. mRNA SYNTHEISIS DOES NOT OCCUR DURING TANSLATION

ALL OTHER OPTIONS ARE DIFFERENT STEPS  DURING TRANSLATION.

tRNA IS AN ADADPTER MOLECULE WHICH READS THE CODES IN THE MRNA AND AT THE SAME TIME BIND TO SPECIFIC AMINO ACIDS   . tRNA HAS AN ANTICODON LOOP THAT HAS BASES COMPLEMENTARY TO THE CODE , AND IT HAS ALSO AN AMINOACID ACCEPTOR END TO WHICH IT BINDS TO AMINO ACIDS . COMPLEMENTARY BASE PAIRING OCCURS BETWEEN THE CODON IN THE mRNA AND ANTICODON IN THE tRNA. THE ORDER AND SEQUENCE OF AMINO ACIDS ARE DEFINED BY THE SEQUENCE OF BASES IN THE mRNA. THE AMINOACIDS ARE JOINED BY BOND WHICH IS KNOWN AS PEPTIDE BOND.

AMINOACIDS ARE ACTIVATED IN THE PRESENCE OF ATP AND LINKED TO THEIR COGNATE tRNA . THIS IS KNOWN AS CHARGING OF tRNA. WHEN TWO SUCH CHARGED tRNAS ARE BROUGHT CLOSE ENOUGH THE FORMATION OF PEPTIDE BOND BETWEEN THEM TAKES PLACE.

CELLULAR FACTORY RESPNSIBLE FOR TRNSALTION IS THE RIBOSOME. RIBOSOME HAS TWO SUBUNITS. LARGER SUBUNIT AND SMALLER SUBUNIT.WHEN THE SMALLER SUBUNIT ENCOUNTERS AN mRNA THE PROCESS OF TRANSLATION BEGINS.

A TRANSLATIONAL UNIT IN mRNA IS THE SEQUENCE OF RNA THAT IS FLANKED BY THE START CODON AND THE STOP CODON AND CODES FOR POLYPEPTIDE. FOR INITIATION , THE RIBOSOME BINDS TO THE mRNA AT THE START CODON . DURING ELONGATION COMPLEXES COMPOSED OF AN AMINOACID LINKED TO tRNA , SEQUENTIALLY BIND TO THE APPROPRIATE CODON IN mRNA BY FORMING COMPLEMETARY BASE PAIRS WITH THE tRNA ANTICODON. THE RIBOSOME MOVES FROM CODON TO CODON ALONG THE mRNA . AMINO ACIDS ARE ADDED ONE BY ONE JOINED BY PEPTIDE BONDS. AT THE END RELEASE FACTOR BINDS TO THE STOP CODON TERMINATING TRANSLATION AND RELEASING THE COMPLETE POLYPEPTIDE FROM THE RIBOSOME