Biology Final Exam Dec 3 Translation of protein synthesis Transfer RNA tRNA is a ribonucleotide about 80 90 nucleotides in length o 3 OH terminus where Amino Acids bind o Anticodon complementary to the codon tRNA forms the anticodons to the mRNA codons 61 Codons that code for Amino Acids o There are less than 61 tRNA Francis Crick Wobble Hypothesis o When the tRNA starts to match its anticodon with the codon on the mRNA The first position of the codon binds first the second codon binds second and the third codon binds last The bonding between the third position of the codon and the third position of the anticodon is more flexible than typical that s why there is fewer tRNA than there are codons that code for amino acids some tRNA can bond to more than one type of codon Examples Don t need to know specifics If the third position of the codon is a U the position of the anticodon that bonds with the U can be an A or G If the third position of the codon is a G the anticodon could bond with a U or a C Charging the tRNA attach an amino acid to the 3 end of the tRNA o Requires an enzyme aminoacyl tRNA synthetase charges the tRNA o What s needed The enzyme aminoacyl tRNA synthetase The appropriate tRNA they differ depending on what their anticodon is the anticodon has to match up with the proper codon the codons specify a specific Amino Acid ATP molecule o If the codon is AUG codes for Methionine the start codon tRNA with the anticodon complementary to AUG will need a Methionine molecule which is the amino acid and an ATP o The tRNA is charged in a 2 step reaction 1 The ATP reacts with the AA You get the AA bonded to AMP Adenosine monophosphate and two phosphates are released 2 The AA bonded to AMP and the tRNA react together to get a tRNA bonded to the AA and AMP is released The first step bonds the AA to AMP beginning with ATP and the second step AA is transferred to the tRNA molecule Ribosome needed for translation o Has a large and small subunit o mRNA binding site small subunit Exit tunnel where the polypeptide made during translation will leave the ribosome o Three important sites found on both the large and small subunit P Site peptidyl site don t need to know Polypeptide a chain of amino acids bonded with peptide bonds A Site Aminoacyl site don t need to know Amino acid E Site Exit Site After a tRNA has lost its amino acid it leaves the ribosome through the E site o Ribosomes of eukaryotes are a little different than those of prokaryotes Many antibiotics that humans use work by interfering with the activity of the ribosomes of bacteria The antibiotics don t hurt people but they kill bacteria o Function of the ribosome The ribosome catalyzes the dehydration synthesis where the water is removed and a new bond Is formed between two amino acids Another way to say it the ribosome catalyzes peptide bond formation during translation of protein synthesis The ribosomes will cause the dehydration synthesis to occur and the peptide bond to form When the peptide bond is formed by the ribosome the bond between the tRNA and AA is broken The ribosome acts as a catalytic RNA molecule called a Translation ribozyme made of RNA o Three Steps Don t get these steps confused with Transcription steps 1 Initiation Involves creating an initiation complex which is made up of mRNA molecule Small subunit of the ribosome mRNA binding site Initiator charged tRNA which is bound to MET Methionine Needs to use a GTP as an energy source and bring in the large subunit of the ribosome 2 Elongation Requires the appropriately charged tRNA proteins call elongation factors and GTP molecules which provide the energy for elongation Step One The elongation factors usher an appropriate charged tRNA into the A site The tRNA is charged with the corresponding amino acid o Ex the codon AAA causes the tRNA is charged with the amino acid lysine CCC causes the tRNA is charged with the amino acid proline The instant the tRNA goes into the A site a peptide bond is formed between the two amino acids o Ex the Amino Acid lysine is bonded to proline The ribosome shifts to the right one codon on the mRNA The tRNA in the P site moves to the E site where it exits The tRNA in the A site with the peptide bonded to it then moves to the P site The A site is now vacant the tRNA that was in the A site and has the peptide bonded to it is now in the P site The GTP is used when the ribosome is shifted one codon downstream the mRNA Elongation Factors bring in the next charged tRNA o Ex GGG codon codes for the amino acid Glycine The peptide bonded to the tRNA in the P site is now at bonded to the tRNA in the A site o Ex The peptide bond is now Lysine proline glycine The ribosome move down one more codon and the cycle continues repeated 3 400 times in seconds Repeated until it reaches a stop codon 3 Termination Occurs when a stop codon appears in the A site There is no tRNA with a complementary anticodon for a stop codon Requires release factors and GTP o Release factors proteins bonds into the A site When that happens the bond between the tRNA in the P site and a peptide is broken The final polypeptide product is released through the exit tunnel on the ribosome o The uncharged tRNA is release through the E site and the small and large subunits of the ribosome detach and everything is released o Polyribosome mRNA can be translated by many ribosomes at the same time A single mRNA molecule that is being transferred by many ribosomes at the same time o Prokaryotes have coupled transcription and translation This happens because they don t have a nuclear envelope or nucleus o As soon a mRNA starts being made in transcription a ribosome will grab onto the mRNA and being translation