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:

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

Deceptively simple, but let’s recap the finer points

transcription

translation

DNA

RNA

Protein

Flow of genetic information:

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

(which contains)

Collection of recipes(one is chosen to make)

Recipe card(a disposable copy)

Start with a cookbook Start with DNA

(which is read by)

Chef(s)(interpret(s) words

on card to)

Assemble(s) ingredients

(baked together by)

Oven(yielding)

Cake

(which contains)

Collection of genes(one is chosen to make)

mRNA(a disposable copy)

(which is read by)

tRNAs(interpret codons

on mRNA to)

Assemble amino acids

(joined/bonded by)

Ribosome (rRNA)(yielding)

Protein

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' MetLeuAspPro 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'

• 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

Objectives Achieved