Protein Processing Flashcards
What does eukaryotic mRNA contain?
Codons (in the coding region), 7-methyl guanosine cap at the 5’ end and poly A tail at the 3’ end
What are the two regions of unpaired nts on tRNA that are crucial to its functions?
Anticodon loop, a set of 3 consecutive nts that pair with a complementary codon in mRNA
3’ CCA terminal region which binds the aa that matches the corresponding codon
Describe the activation of amino acids
Aminoacyl tRNA synthetases catalyzes addition of AMP to COOH end of AA
AA transferred to cognate tRNA
What are the three important binding sites of the ribosomal complex and what are their functions?
Acceptor (A) site: where mRNA codon exposed to receive aminoacyl tRNA (except the Met tRNA)
Peptidyl (P) site: where aminoacyl tRNA is attached
Empty or exit (E) site: location occupied by empty tRNA before exiting ribosome
What is the structure of prokaryotic ribosomes?
Large: 50s
Small: 30s
70s complete ribosome
Describe the structure of eukaryotic ribosomes
Large: 60s
Small: 40s
Complete ribosome 80s
Describe the events that occur during the initiation of translation
Pre-initiator complex assembled
Initiator tRNA bound to a GTP attaches to P site of small su
tRNA methionine complex is loaded onto the P site of small su (met-euk and fmet-pro)
Other IFs (pro) and eIFs (euk) are added
Large su added
Translation begins with the initiation codon AUG (codes for met)
Describe the events that occur in elongation of translation
Activated AA attached to initiating met via peptide bond
Amino acyl tRNA is loaded onto the ribosome w/ anticodon base pairing with codon on the A site
Loading accompanied by GTP hydrolysis and release of factor from aminoacyl tRNA
Peptide bond forms between aa in A site and P site catalyzed by peptidyl transferase
Describe the events of termination of translation
Peptide chain release from ribosome complex
Termination triggered by stop codons
Signal ribosome to stop translation
Stop codons are recognized by release factors
Water molecule is added instead of an AA (forms COOH end)
Completed protein released and GTP hydrolysis dissociates ribosome complex
What are polysomes?
Clusters of ribosomes simultaneously translating a single mRNA molecule
Each synthesizing a polypeptide
Makes protein synthesis more efficient
Which three codons are considered to be the stop codons?
UAA, UAG and UGA
List the characteristics of the genetic code
Degenerate (some AA can be coded by more than 1 codon and 3 codons do not code for any AA)
Standard but not universal
Not punctuated and is without commas
Non-overlapping (with some exceptions)
Which codons codes for Met (M)?
AUG
Why is it important to study the difference between prokaryotes and eukaryotes?
To be able to selectively inhibit prokaryotic protein synthesis (clinical use - molecular basis for Abx)
To be able to understand the mechanism of human disease (research use - allow for the development of Tx and/or prevention)
Name the prokaryotic translation inhibitors
Streptomycin, clindamycin and erythromycin, tetracycline, and cholamphenicol
Name the eukaryotic translation inhibitors
Shiga toxin and ricin, diptheria toxin and cycloheximide
How does the abx streptomycin work?
Binds to 30s subunit and interferes with the binding of fmet-tRNA and impairs initiation
Interferes with 30s subunit association with 50s subunit
How do the abx clindamycin and erythromycin work?
Bind to large 50s subunit blocking translocation of the ribosome
How does the abx tetracycline work?
Binds to small 30s su blocking entry of aminoacyl-tRNA to ribosomal complex and impairs elongation
How does the abx cholamphenicol work?
Inhibits peptidyl transferase activity and impairs peptide bond formation
How do shiga toxin and ricin work as eukaryotic translation inhibitors?
Binds to large 60s subunit blocking entry of aminoacyl-tRNA to ribosomal complex
How does diptheria toxin inhibit translation in eukaryotics?
Inactivates GTP bound EF-2 interfering with ribosomal translocation