Fig. 9-1
Chapter 9: Proteins and their synthesis
Coupled transcription/translation Compartmentedtranscription/processing/translation
Fig. 9-2
Proteins are polymers of amino acids joined through peptide bonds
Each protein has a amino- and a carboxyl-terminus
The function of a protein is dependent upon its overall structure; each level of protein structure is dependentupon lower levels; thus, all are derivatives of primary structure of the polypeptide
The primary structures of polypeptides are directly derived from the primary structures of their mRNAs
Primary structures of mRNA are derived from the primary structures of their DNA templates (± splicing)
Changes in DNA sequence can alter function of proteins encoded by that DNA sequence
Fig. 9-3
Protein higher order structures
amino acid sequence
Regular coil/sheet motifs stabilized by H-bonds between peptidyl atoms
specific intramolecular folding stabilized by associations of amino acid “R” groups
intermolecular associations stabilized by associations of amino acid “R” groups
Tertiary and quaternary structures are determined by primary structure
Fig. 9-5
Genes encode the primary structure of proteins
E. coli trpA mutations: genetic map is co-linear with the protein(C. Yanofsky)
Degeneracy in the codon-amino acid code derives from:
• Multiple codons for certain same amino acids
e.g., UCUUCCUCA serineUCGUGUUGC
Degeneracy in the codon-amino acid code derives from:
• Multiple codons for certain same amino acids
e.g., UCUUCCUCA serineUCGUGUUGC
• “Wobble” permits certain individual tRNAs to pair with multiple codons
Fig. 9-15
Three significant domains of ribosome during translation:
A: incoming aminoacyl-tRNA binding siteP: peptidyl-tRNA binding siteE: exiting deacylated-tRNA site
Fig. 9-18
Three phases of translation:
Initiation:
• association of small subunit and capped 5’ end of mRNA• association of Met-tRNA (fMet)• scanning to AUG (eukaryotes)• association of large subunit
Three phases of translation:
Initiation
Elongation
• aa-tRNA association with A site• transfer of peptidyl to aa-tRNA• translocation (next codon)• exiting of deacylated tRNA
Fig. 9-19
Three phases of translation:
Initiation
Elongation
Termination
• stop codon recruits release factor• hydrolysis of peptidyl-tRNA link• release of complex
Fig. 9-21
Translational suppressors:
mutant tRNAs with modified anticodons that permit “readthrough” of nonsense mutations
Fig. 9-23
Posttranslational modifications of proteins:
• protein folding into “native” configuration (assisted by chaperones)
• covalent modifications of amino acid side chains
• targetting to specific intra- and extracellular sites
All subject to mutation in the protein or in the cellular machinery that modifies the protein