Genetic Code Codons composed of three nucleotides in RNA Codon specifies amino acid or stop Genetic code is redundant

Genetic Code Table

Reading Frames One of three possible reading frames contains protein message

Mutations In Protein-Coding Sequences Missense Change to codon for different amino acid SilentChange to codon for same amino acid Nonsense Change to stop codon Insertion/ Usually disrupt reading frame deletion

Adaptors for associating codons with amino acids Cloverleaf structure Anticodon recognizes codon by complementary base-pairing Transfer RNA

Wobble Base-pairing Relaxed base-pairing at third position of codon tRNA may recognize multiple codons

Modified Nucleotides In tRNA post-transcriptional modifications

Different synthetase for each amino acid Amino acid attached to tRNA by high energy ester bond Aminoacyl-tRNA Synthetases

Sequential Action Of Adaptors

Editing By Synthetases Active site may mistakenly bind related amino acid Incorrect amino acid is hydrolyzed at editing site

Growth Of Polypeptide Stepwise growth from N-terminus to C-terminus

Large and small subunits Composed of rRNA and proteins Ribosome Structure

Translation On Ribosome P site contains tRNA attached to growing polypeptide A site binds incoming aminoacyl-tRNA Peptide bond formation by peptidyl transferase of ribosome Translocation of ribosome

EF-Tu:GTP interacts with A site Codon-anticodon interaction leads to hydrolysis of GTP and dissociation of EF-Tu EF-G promotes ribosome translocation Elongation Factors

Diphtheria Toxin Transfer of adenosine diphosphate ribose to EF-2 Inhibits EF-2, which impairs ribosome translocation

Initiation In Eucaryotes Methionine-linked initiator tRNA to small ribosome P site (eIF-2) Load onto mRNA 5’ end (eIF-4E, eIF-4G, polyA) Scan for AUG Assemble large ribosomal subunit

Initiation In Bacteria Formylmethionine-linked initiator tRNA Small ribosome subunit binds to Shine-Dalgarno sequence Polycistronic mRNAs

Termination Stop codons not recognized by tRNA Release factors bind to A site Addition of H 2 O to peptidyl-tRNA

Polyribosomes Multiple ribosomes translating same mRNA Interaction of mRNA 5’ and 3’ ends

Selenocysteine Selenocysteine tRNA is charged with serine that is subsequently converted Encoded by UGA codon followed by special signal

Antibiotics Tetracyclineblocks binding of aminoacyl- tRNA to A-site of ribosome Streptomycinprevents the transition from initiation complex to chain-elongating ribosome; causes miscoding Chloramphenicolblocks the peptidyl transferase reaction on ribosomes Erythromycinblocks the translocation reaction on ribosomes Rifamycinblocks initiation of RNA chains by binding to RNA polymerase

Folding During Synthesis Individual domains folded rapidly after their synthesis

Creating Functional Proteins Association with cofactors, proteins Covalent modifications

Molecular Chaperones Prevent inappropriate aggregation during folding Recognize exposed hydrophobic regions Hydrolyze ATP Heat shock proteins

Hsp70 Chaperones Act early Repeated cycles of target binding & release mediated by ATP binding & hydrolysis

Hsp60 Chaperones Chaperonins Isolation chambers Cycles of target confinement & release mediated by ATP binding & hydrolysis

Protein Quality Control Exposed hydrophobic regions indicate misfolding Selective degradation of proteins that cannot be correctly folded

Proteasome Protease activity in interior of cylinder Caps function in ATP- dependent unfolding and as gates for selective entry

Attachment Of Ubiquitin Attached to lysine on target; multiubiquitin chains Ubiquitin attaches to E1 Transferred to E2 of ubiquitin ligase E3 of ubiquitin ligase recognizes degradation signal

Regulated Degradation Modification of an E3 protein Modification of a target protein

Disease From Protein Aggregation Aggregates of misfolded proteins Cross-beta filaments Neurodegeneration- Huntington’s, Alzheimer’s, Prion diseases (Creutzfeldt- Jacob, bovine spongiform encephalopathy)