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. 9-4

Fig. 9-5

Genes encode the primary structure of proteins

E. coli trpA mutations: genetic map is co-linear with the protein(C. Yanofsky)

Fig. 9-8

Degeneracy in the codon-amino acid code derives from:

• Multiple codons for certain same amino acids

e.g., UCUUCCUCA serineUCGUGUUGC

Fig. 9-10

tRNAs convert the codon-amino acid codemediated by aminoacyl synthetases

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. 9-12

“Wobble” creates partial ambiguity in codon 3’

nucleotides

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

Fig. 9-1