Outline Review the central principle in the flow of genetic information Revisit the idea that building a protein is like baking a cake Focus on translation: the “who, where, and how” of protein building Apply what we’ve learned

Review DNA stores instructions for the synthesis of proteins using RNA as an intermediate Proteins = polymeric chains of amino acids; vital roles in cells include speeding up chemical reactions, transport, communication, structural support, movement & defense Flow of genetic information: DNA transcription RNA translation Protein Deceptively simple, but let’s recap the finer points

Last time we discussed… Protein synthesis is similar to cake baking Both require: instructions (recipes = genes) disposable copy (recipe card = mRNA) interpreter (chef = tRNA) Equipment to associate ingredients (oven = ribosome (rRNA))

Cake Baking Protein building Start with a cookbook Start with DNA (which contains) (which contains) Collection of recipes Collection of genes (one is chosen to make) (one is chosen to make) Recipe card (a disposable copy) mRNA (a disposable copy) (which is read by) (which is read by) Chef(s) tRNAs (interpret(s) words on card to) (interpret codons on mRNA to) Assemble(s) ingredients Assemble amino acids (baked together by) (joined/bonded by) Oven Ribosome (rRNA) (yielding) (yielding) Cake Protein

Transcription vs. Translation The first half (transcription) of each process is dedicated to the copying of information The second half (translation) is dedicated to the deciphering of coded instructions and synthesis of final product It is the latter on which we now will focus

Translation Players: mRNA (recipe card copy), tRNAs (chefs)*, amino acids (ingredients), and ribosome (oven) Location: cytoplasm Occurs in Three Steps: 1) Initiation  2) Elongation  3) Termination * - tRNAs bring in correct amino acids by “reading” triplet clusters of ribonucleotide bases on mRNA molecule, called codons, through base-pairing with tRNA’s anticodon region mRNA

Initiation Small ribosomal subunit binds to mRNA Initiator tRNA binds to start codon Large ribosomal subunit binds Initiation complex is complete

Elongation Codon recognition (in “A” site) Peptide bond formation Translocation (tRNA in “A” is now in “P” site) Process repeats and polypeptide chain grows

Termination Stop codon encountered (in “A” site) Release factor protein binds Completed polypeptide is freed from last tRNA Ribosomal complex falls apart

Cracking the “nucleotide code” Purpose: to know what three-letter “words” (codons) code for particular amino acids When: By 1966 scientists deciphered the 64 RNA codons for all 20 amino acid building blocks Result: a (nearly universal) cipher (pictured below) Importance: allows us to predict a resulting polypeptide chain’s amino acid sequence from any gene’s nucleotide sequence

Practicing What We’ve Learned Let’s find the amino acid sequence (in 3-letter abbreviation) of the polypeptide product that would result from the following mRNA sequence and review translation: 5'-GAGGUAUGUUGGACCCCUGACAUG -3' Met Leu Asp Pro Stop

Practicing Independently Using the chart provided, give the amino acid sequence (in 3-letter abbreviation) of the polypeptide product that would result from the following mRNA sequence; underline the start codon and circle the stop codon: 5'-GAGGUAUGAAUGUAUGGUCACAUGAGUUAUAGCAA -3'

Objectives Achieved Know DNA directs synthesis of proteins using RNA as an intermediate Differentiate between the steps involved in transcription vs. translation Identify the players involved in the process of translation, where this process take place, and the steps of protein synthesis Predict a protein’s a.a. sequence using the genetic code