T RANSLATION The next step in manufacturing a protein involves translating the mRNA formed in transcription to a protein In translation, the encoded message is read, codon by codon, by a ribosome, and with the presence of transfer RNA molecules, the ribosome assemble one amino acid at a time into a polypeptide chain

One wrong letter: o Translation: PSTQ

In translation, information present in the mRNA is read by the ribosome to synthesize a polypeptide. W HAT T RANSLATION A CCOMPLISHES

T RANSLATION HAS MANY COMPONENTS..

T RNA tRNA have regions of base pair, with 4 double helical segments to form a clover leaf shape At one tip, has an segment called an anticodon sequence of 3 nucleotides that pairs with a codon from the mRNA

T RNA Example Codon: 5’ AGU 3’ Antidon 3’ UCA 5 When tRNA is linked to its correct amino acid, it is called: aminoacyl-tRNA

tRNA Is An Adaptor That Couples Codons and Amino Acids

R IBOSOMES Carry out protein synthesis by translating mRNA into chains of amino acids Ribosome is made up of 2 different size parts called the large and small ribosomal sub units Each sub unit is made up of a combination of rRNA and ribosomal proteins

Ribsome has special binding sites that bring together mRNA and the aminoacyl-tRNA 3 sites= A,P & E A site (amino acyl): where incoming amino acyl-tRNA carrying the next amino acid to be added to the polypeptide chain, binds to the mRNA P Site (peptidyl) : the site where the tRNA, carrying the growing peptide chain is bound E Site (exit): exiting tRNA leaves ribosome R IBOSOMES

T HE P ROCESS OF T RANSLATION HAPPENS IN 3 STEPS : 1.I NITIATION 2.E LONGATION 3.T ERMINATION

I NITIATION The first amino acyl-tRNA of the new protein chain becomes bound to the AUG start codon This is called the initiator methionine- tRNA It forms a complex with the small ribosomal unit This complex binds to the mRNA at the 5’ cap and then moves along the mRNA until it reaches the first AUG codon this is the start codon and is recognized by the anti codon of MET-tRNA

The large ribosomal unit then binds to complete the ribosome at the end of initiation The initiator MET-tRNA is in the P site Correct initiator tRNA-AUG pairing establishes the correct reading frame ; the series of codons for the polypeptide that is encoded by the mRNA A large and small ribosomal subunits connect to an mRNA molecule I NITIATION

E LONGATION This is a 4 step process

E LONGATION : S TEP 1 Begins when the initiator tRNA, with its attached methionine, becoming bound to the P site of the ribosomal unit

E LONGATION : S TEP 2 appropriate anti-codon and amino acid binds to the codon in the A site The amino acid is cleaved from the tRNA in the P site and forms a peptide bond with the amino acid on the tRNA in the A site Peptidyl transferase is the enzyme that allows this to happen EPA

E LONGATION : STEP 3 the ribosome moves along the mRNA to the next codon the two tRNAs remain bound to their respective codons An appropriate tRNA moves into the A site and steps 2 and 3 are repeated After each repeat the empty tRNA that was in the P site moves to the E site

E LONGATION S TEP 4 the empty tRNA is released from the ribosome

T ERMINATION Translation switches from the elongation to the termination stage when the A site of a ribosome arrives at one of the stop codons (UAA, UAG, or UGA) on the mRNA Because no amino acid is present at the A site the polypeptide chain is detached and ribosomal subunits separate from mRNA

T RANSLATION IN E UKARYOTES AND P ROKARYOTES In both eukaryotes and prokaryotes multiple ribosomes can translate an mRNA molecule at the same time, thereby increasing the production of crucial proteins Polysome is a complex that is formed when multiple ribosomes attach to the same mRNA in order to facilitate rapid translation

F ROM P ROTEIN TO P OLYPEPTIDE The polypeptide that has been assembled by the ribosome is still not functional The protein exists in an inactive state Since the shape of the protein defines its function, the polypeptide chain must be folded into the correct confirmation Enzymes will carry out processes that turn this polypeptide into its functional shape and join various polypeptide chains together if needed

These are the words of the genetic language. R EMEMBER THE G ENETIC C ODE …

Translation Is a Cyclic, Multistep Process