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Lecture 14

Lecture 14- Translation.docx

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Biology 1202B
Brenda Murphy

Lecture 14: Translation – mRNA  Protein Translation - The assembly of amino acids into polypeptides - In prokaryotes this process take place throughout the cell - In eukaryotes this takes place mostly in the cytoplasm 1. ) mRNA – Messenger RNA - 100s of nucleotides long - Template for translation - Read in a 5’ to 3’ orientation 2. ) tRNA –Transfer RNA - Bring amino acids to the ribosomes for addition to the polypeptide chain - 75 – 90 nucleotides long - Internal anticodon (3-nucleotide segment) is complimentary to mRNA codons - tRNA and mRNA bind antiparallel to one another – ex. tRNA linked to Seranine pairs with codon AGU in mRNA. The anticodon of the tRNA that pairs with this is UCA - Attached to 3’ prime end is an amino acid specific to the anticodon distinctive structures Cloverleaf - 2 dimensional Structure of tRNA - Anticodon is at the bottom of the structure - You could predict what the anticodon is because of the genetic code. More than one codon that codes for a protein. - Amino acid attaches to the transfer end of the tRNA – it has to be charged – amino acylation (the addition of an amino acid) - 3 nucleotides complementary to mRNA - Wobble Hypothesis: the third nucleotide can change but still codes for the same amino acid (most of the time) L Shape – 3 dimensional structures - How it actually is formed in the body 3. ) rRNA – protein complexes - Small and large subunits - Each subunit is made of rRNA and ribosomal proteins - Translates mRNA into amino acid - Amino acids are joined together to a polypeptide chain Ribosome Structure - E – exit site (left) - P – peptidyl site (middle) - A – Amino acid site (right) amino acids on tRNA are transferred and joined together to make the polypeptide sequence Overview of Translation - Occurs in the cytoplasm - Movement of tRNA’s coming into the site - The A site is where a new tRNA is coming in (right) - P site is where the amino acids are being added to the chain - Then when it is done it moves to the E site and exits - Each mRNA to tRNA is antiparallel binding, tRNA contains complimentary binding of nucleotide sequence - Ribosome structure moves along the mRNA, until an inhabited amino acid comes in - mRNA is 5’ – AGU 3’– amino acid serine - Anticodon 3’ – UCA 5’ 3 Major Stages in Translation Initiation  Assembly of all the translation components on the start codon of the mRNA  Large and small ribosomal units bind to an mRNA molecule  The initiator tRNA molecule carrying the amino acid Met binds to the AUG start codon at the P site.  Application: What if mRNA has a mutation in the start codons A, T or G. Will the transcript be translated? No, because it cannot recognize the start codon Elongation  Reading the string of codons in the single stranded mRNA and changing this information into a string of amino acid
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