Draw the typical structure of mRNA
What is the sequence for a start codon and what amino acid does it code for?
AUG and Methionine
Draw a diagram showing how an amino acid becomes attached to tRNA.? Include the name of the enzyme
List the steps for Initiation
Step 1: dissociation of ribosome subunits (eukaryotic 40S + 60S)
Step 2: assembly of preinitiation complex containing Met-tRNA + eIFs + 40S subunit
Step 3: binding of mRNA to preinitiation complex
Step 4: binding of 60S subunit
Draw a diagram illustrating the steps for initiation
List the steps for Elongation?
Step 1: binding of new tRNA carrying second amino acid to “amino acyl” (A) site
Step 2: catalysis of peptide bond formation between the two amino acids by peptidyl transferase (PT) on the large ribosomal subunit
Step 3: translocation of tRNA to P site and dissociation of first tRNA from E site
Name the 3 sites on a ribosome
E P A add pic
Draw a diagram illustrating the steps for Elongation
List the steps for Termination
Step 1: recognition of stop codon Step 2: release of peptide chain Step 3: dissociation of release factors and ribosomes add pic
Explain why some antibiotics inhibit protein synthesis in prokaryotes but not in eukaryotes?
Translational machinery is complex, easily disrupted – common target for antibiotics Antibiotics exploit differences between prokaryotic and eukaryotic ribosomes and translation factors
What is a signal sequence?
First 20-24 amino acids = “signal sequence” (enriched in hydrophobic amino acids, e.g. Leu, Ile, Phe, Trp, Tyr, Ala)
Synthesis of proteins destined for the secretory pathway to the cell surface occurs on RER in the following stages: List these stages.
Step 1: Recognition of hydrophobic signal sequence by signal recognition particals (SRP)
Step 2: Binding of SRP to a receptor on the RER surface, translation resumes
Step 3: Translocation of growing peptide into the lumen of RER
Step 4: cleavage of signal sequence and protein folding
Transmembrance proteins have additional hydrophobic sequences that stick in the membrane of the RER
Summarise the ways in which newly-synthesised proteins can be post-translationally modified
• Disulphide bond formation (e.g. insulin) • Proteolytic cleavage (e.g. insulin -> A and B chains) • Addition of carbohydrate (Glycosylation) • Addition of phosphate (Phosphorylation) • Addition of lipid groups (Prenylation, Acylation) • Hydroxylation (e.g. Collagen; Leitinger lecture)