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murphy summ lec 4- translation .doc

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Biology 1202B
Shauna Burke

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Lecture 4- Translation [ mRNA → Protein (info encoded in nucleotides, converted to other molecule i.e. A.A ) ] Translation & RNA mRNA: 100s of nucleotides lonG, template for translation, read in a 5’→ 3’ orientation tRNA: 75-90 nucleotides long, internal anticodon sequence is complementary to mRNA codon, tRNA and mRNA bind in an antiparallel manner, attached to 3’ end is an amino acid specific to the anti- codon dis- tinctive structure *anticodon is complementary to the sequences in the Mrna, RNA is always single strand- ed* parts of the cloverleaf structure is double stranded, the loops = where the RNA is sin- gle stranded the amino acid on the 3’ chain are the ones that make up the polypeptide *Aminoacy- lation or charging wobble hy- pothesis: the 3rd nucleotide can change and wont make a big diff, al- lows for flexibility 3 nucleotides complementary to mRNA Wobble Hypothesis: codon’s 3rd nt binding non watson and crick binding between the double strand to allow for space when binding with oth- er things Transla- tion and RNA mRNA: tem- plate for translation,read in a 5’→ 3’ orientation tRNA: internal anticodon sequence is complementary to mRNA codon, tRNA and mRNA bind in an antiparallel manner, attached to 3’ end is an amino acid specific to the anticodon rRNA-protein complexes small & large subunits, each subunit is made of rRNA and ribosomal proteins, where translation of mRNA to amino acid occurs, where amino acids are joined together to make a polypeptide chain (protein) E = exit site P= peptidyl site A= aminoacyl site ribosome facilitates the binding of tRNAs to the codon adn the formation of the pertide bond between A.A incoming tRNA with A.A attached, reads codon and introduces amino acid to be added next * Ser is always the first A.A . 3 Major Stages of Translation initiation:assembly of all the translation components on the start codon of the mRNA elongation: reading the string of codons in the single stranded mRNA and changing this info into a string of A.A i.e. addition of sing AA to growing polypeptide chain termination: releasing the string AA ( protein polypeptide chain) from the ribosome. Disas- sembly of the ribosome subunits and mRNA. MET= a.a required for initiation, 3’ end : UAC 1. Met-tRNA with GTP bound t it and the small ribosomal unit form a complex * GTP provides energy for large ribosome unit to bind to small unit and met-tRNA at P site 2. the complex binds to the 5’ cap of the mRNA and scans along it until it reaches AUG start codon 3. the large ribosomal subunits binds and GTP is hy- drolyzed, completing initiation. 1. an aminoacyl tRNA binds at the A site 2. peptidyl transferase cleaves the A.A from the P site tRNA and bonds it to the AA on the A site of the tRNA GTP→GDP + Pi provides the energy when an aninoacyl-tRNA binds to A site 3. the ribosome translocated along the mRNA to the next codon, thereby bringing the tRNA with the growing polypeptide to the P site and moving the empty tRNA to the E site GTP provides energy to shift both tRNA left as ribosome translocates right 4. when translocation is complete, the empty tRNA in the E site is released and the cycle is ready to go again. Growing polypeptide moves thru the exit tunnel of the large unit Met does exist in the mRNA, the first one only acts as the start codon Translation Elonga- tion 1-3 cy- cles/sec in eukaryote, 15-20 cycles/sec in prokaryote prok: faster, b/c there system are not as com- plex as euk . Translation Termina- tion 1. the ribo- some
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