Translation of Genetic Code - PDF

Translation Process of converting information that is stored in nucleic acid sequences into proteins The Genetic Code  The Genetic Code A Code is triplet. – Each codon in mRNA specifies 1 amino acid. -...

Translation Process of converting information that is stored in nucleic acid sequences into proteins The Genetic Code  The Genetic Code A Code is triplet. – Each codon in mRNA specifies 1 amino acid. - Loading…  the 1st associateadote I nuc lesticles are the withexpect same andM most impor tant M & O O  The Genetic Code Code is triplet. – Each 3 codon in mRNA specifies 1 amino acid. Code is comma free. – mRNA is read continuously, 3 bases at a time without skipping bases. Loading…  The Genetic Code Code is triplet. – Each 3 codon in mRNA specifies 1 amino acid. Code is comma free. – mRNA is read continuously, 3 bases at a time without skipping bases. Code is non-overlapping. – Each nucleotide is part of only one codon and is read only once..odood , 00  The Genetic Code Code is triplet. – Each 3 codon in mRNA specifies 1 amino acid. Code is comma free. – mRNA is read continuously, 3 bases at a time without skipping bases. Code is non-overlapping. – Each nucleotide is part of only one codon and is read only once. Code is almost universal. – Most codons have the same meaning in different organisms  Genetic Code & Code is degenerate. – 18 of 20 amino acids are coded by more than one codon. Met and Trp are the only exceptions.  Genetic Code Code is degenerate. – 18 of 20 amino acids are coded by more than one codon. Met and Trp are the only exceptions. Code has start and stop signals. -- AUG codes for Met and is the usual start signal. UAA, UAG, and UGA are stop codons and specify the the end of translation of a polypeptide.  Genetic Code Code is degenerate. – 18 of 20 amino acids are coded by more than one codon. Met and Trp are the only exceptions. Code has start and stop signals. AUG codes for Met and is the usual start signal. UAA, UAG, and UGA are stop codons and specify the the end of translation of a polypeptide. Wobble occurs in the tRNA anti-codon. – 3rd base is less constrained and pairs less specifically. with the ERNA  The Wobble Occurs at 3’ end of codon = 5’ end of anti-codon. Result of arrangement of H- bonds of base pairs at the Jareimport Loading… 3rd position. Degeneracy of the code is such that wobble always isn't as strong results in translation of the same amino acid. of banding not a mu. Complete set of codons can tation can be read by fewer than 61 Still wead to tRNAs. the same result The Players  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. tRNA 3 ′ Amino acid attachment site at the 3′ single-stranded 5 when -RNA binds to amino region ′ acid , it's Different tRNA molecules charged encoded by different Stem- Hydrogen loop genes bonds G G C structure tRNASer carries serine Anticodo n (a) Two-dimensional structure of tRNA Common features 5 ′ – Cloverleaf structure 3′ single – - Anticodon strande d – Acceptor stem for region amino acid binding Anticodo 0 n (b) Three-dimensional structure of tRNA  Overall ribosome shape determined by rRNA - Discrete for sizes tRNA binding a polyp a – – P site – Peptidyl site A site – Aminoacyl site synthesis. – E site – Exit site Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Polypeptide 50S subunit 50S subunit E site E site A tRN site P site A A P site E P A site 30S subunit mRN 30S subunit A 5 3 ′ ′ (a) Bacterial ribosome model based on X-ray diffraction 0 Schematic model for ribosome (b) studies structure a: Reprinted from Seth A. Darst, “Bacterial RNA polymerase,” Current Opinion in Structural Biology, 11(2):155–62, © 2001, with permission from Elsevier  Steps to Translation Charging tRNA Initiation Elongation Termination  Step 1-Charging of tRNA (aminoacylation) 1. Amino acids are attached to tRNAs by aminoacyl-tRNA synthetase. There are 20 amminoacyl-tRNA synthases capable of “charging” all tRNAs. tRNAs possess Specific da-tRNAny therese - recognition site. ↓ requires ATp  Step 1-Charging of tRNA (aminoacylation) 1. Amino acids are attached to tRNAs by aminoacyl-tRNA synthetase. There are 20 amminoacyl-tRNA synthases capable of “charging” all tRNAs. tRNAs possess specific aa-tRNA synthetase recognition sites. · uses energy derived from AP hydro a ,  Step 1-Charging of tRNA (aminoacylation) 1. Amino acids are attached to tRNAs by aminoacyl-tRNA synthetase. There are 20 amminoacyl-tRNA synthases capable of “charging” all tRNAs. tRNAs possess specific aa-tRNA synthetase recognition sites. Uses energy derived from ATP hydrolysis.  Step 1-Charging of tRNA (aminoacylation) 1. Amino acids are attached to tRNAs by aminoacyl-tRNA synthetase. There are 20 amminoacyl-tRNA synthases capable of “charging” all tRNAs. tRNAs possess specific aa-tRNA synthetase recognition sites. Uses energy derived from ATP hydrolysis. Produces a charged tRNA (aminoacyl-tRNA).  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. tRNA Amino ATP acid Charge P P P d tRNA P Aminoacyl-tRNA P synthetase PP i AM Pyrophosphat P e 3 The correct tRNA 4 The charged 2 The amino acid is 1 A specific amino acid binds to the tRNA is released. activated and ATP bind to synthetase. by the covalent binding of if aminoacyl-tRNA synthetase. AMP, and pyrophosphate is released. The amino acid is covalently attached to no change, the tRNA. AMP is transcription released. will slow down 0 Initiation, Elongation and Termination  Translation Initiation – a functionally competent ribosome is assembled in --- the correct place on the MRNA and ready to start ----------------------------------------------------------------------- Elongation protein synthesis – tRNA brings the correct amino acid to the ribosome, es it is joined to the nascent polypeptide chain and the -- movestothenext triple fire assembly ----------------------------------------------- any as Termination – a stop codon is reached and the entire assembly dissociates to release the newly-synthesized polypeptide.  Prokaryotic vs Eukaryotic Translation Prokaryotes Eukaryotes Transcription Translation occurs in cytoplasm and translation No Shine-Dalgarno sequence; – Initiation factor (If-uf binds to the -------------------------------------------------------- occurs simultaneously – scop ---------- on the mature MRNA Eukaryote AUG codon is embedded in a Eine - - Belgarna sequences Initiating tRNA is short initiation sequence called the Kozak sequence. Initiating tRNA is methionine formyl- methionine  Initiation Binding of 30S subunit and Initiation Factors If I – - – associates with 30S subunit in the A site preventing a tRNA from entering – -573 – allows for 30S subunit to bind to specific site of mRNA, checks for accuracy of binding of first aa tRNA – If2-ETP - – binds to 30S P site upon which fmet-tRNA binds to IF2 and IF2 moves it to P site. Hydrolysis of GTP occurs after 50S subunit arrives - conformational change & 70S ribosome Step 2-Initiation-steps (prokaryotes): end of & 17 Shine-Dalgarno sequence is complementary to 3’ 16S rRNA. 2) Initiator tRNA (fMet tRNA) binds AUG (with 30S subunit). mRNA 5’-AUG-3’ start codon tRNA 3’-UAC-5’ anti-codon comprised Of proteins and - somal & RNA ↓ has catalytic activity  where Crux the only time the mRNA isn't needed. translation video Step 2-Initiation-steps (prokaryotes): Shine-Dalgarno sequence is complementary to 3’ 16S rRNA. Initiator tRNA (fMet tRNA) binds AUG (with 30S subunit). mRNA 5’-AUG-3’ start codon tRNA 3’-UAC-5’ anti-codon 3. IF3 is removed and recycled. Step 2-Initiation-steps (prokaryotes): Shine-Dalgarno sequence is complementary to 3’ 16S rRNA. Initiator tRNA (fMet tRNA) binds AUG (with 30S subunit). mRNA 5’-AUG-3’ start codon tRNA 3’-UAC-5’ anti-codon IF3 is removed and recycled. IF1 & IF2 are released and GTP is hydrolysed, catalyzing the binding of 50S rRNA subunit. Loading… Results in a 70S initiation complex (mRNA, 70S, fMet-tRNA)  Elongation Elongation Factors and Elongation  At each start Elongation A site is empty P site contains the peptidyl tRNA E site contains an uncharged tRNA - Requires EF-Tu , EF-Ts , EF-G EF-TU-GTP - recognizes and transports aminoacyl-transfer RNAs to the &A site of the ribosome. 6 EF-Tu is released from the ribosome upon hydrolysis of EF-Tu bound GTP to GDP. Als Hydrolysis of GTP is triggered by codon-anticodon pairing at the ribosome. – - reactivates EF-Tu by causing the release of GDP from EF-Tu. – Ef -Ecatalyzes the tRNA/mRNA translocation - nees double cheekers to see if the proper RNA is sent to the A Site.  Elongation Peptide bond formation via peptidyltransferase which is a ribozyme – Activity catalyzed by the 23S rRNA Translocation – New peptidyl tRNA to P-site – - tRNA to E side EF-G-GTP required by unchanged +RNA binding A site and to blocking Release Factors (RFs) aminodage. blocking – GTP is hydrolyzed and EF-G dissociates.  Formation of the peptide bond. Two aminoacyl-tRNAs positioned in the ribosome, one in the P site (5’) and another in the A site (3’). Bond is cleaved between amino acid and tRNA in the P site. Peptidyl transferase (catalytic RNA molecule - ribozyme) forms a peptide bond between the free amino acid in the P site and aminoacyl-tRNA in the A site. tRNA in the A site now has the growing polypeptide attached to it (peptidyl- tRNA). ins spo Because GTP hydrolysis is slow, the site can be checked to ensure the correct aminoacyl tRNA has been placed.  Step 4-Termination of translation: 1. Signaled by a stop codon (UAA, UAG, UGA). 2. Stop codons have no corresponding tRNA. 3. Release factors (RFs) bind to stop codon and assist the ribosome in terminating translation. and UAG 1. RF1 - recognizes LAA UGA 2. RF2 - recognizes VAA and 3. RF3 - Stimulates termination 4. Termination events are triggered by release factors: transferase 1. Peptidyl ------------(same enzyme that forms peptide bond) releases polypeptide from the P site. 2. tRNA is released. (release factors 3. - Ribosomal subunits and RF separate from mRNA Termination phosphorylation