Bio 4 - Protein Synthesis Flashcards
What composes the 3’ end of a tRNA molecule?
A Hydroxyl group, ending with the sequence CCA.
At which part of the tRNA does Aminoacyl tRNA synthetase work in order to “charge” the tRNA?
It works at the 3’ end.
Where do tRNA and mRNA come together to build polypeptides?
In the ribosome.
Where are ribosomes synthesized?
Ribosomal subunits are made in the nucleus, then transported into the cytoplasm.
What are the 2 subunits of ribosomes in Eukaryotes?
60S and 40S. They come together to form 80S ribosome.
What are the 2 subunits of ribosomes in Prokaryotes?
50S and 30S to form 70S ribosomes. Inside the 50S subunit, there is a 23S part.
What are the 3 phases of protein synthesis inside the ribosome?
Initiation, elongation, termination.
Describe initiation in the protein synthesis step in Prokaryotes.
Begins with initiation factor 2 (IF-2). It binds to 30S, then binds to methionine tRNA (the one with a start codon). Then 50S comes, hydrolyzes the GTP on the IF-2, releasing energy to attach to the 30S, kicking the IF-2 and combining to make a 70S. Lastly, the tRNA with methionine (start codon) attaches to the P site.
What are the 3 sites of the ribosome complex where the tRNA can combine?
A site (where incoming aminoacyl tRNA binds), P site (where the polypeptide tRNA binds, where the growing polypeptide chain is found), E site (where the now empty tRNA is moved so it can exit the ribosomal unit). The fist tRNA (the one containing the start codon) is in the P site.
Describe the elongation process in protein synthesis in the ribosome.
The tRNA containing the next codon binds to the A site with the help of the Elongation factors (EF). Then, Peptidyltransferase, fond in the 50S, transfer the peptide that is bound to tRNA in the P site, to the peptide that is attached to the tRNA in the A site. Then translocation happens (shifts both tRNAs into the next sites). The empty tRNA that is now in the E site gets kicked off.
What is the elongation factor found in prokaryotes?
Elongation facto G.
What is the elongation factor found in eukaryotes?
Elongation factor 2.
Which bacteria toxins inhibit Elongation factor 2?
Diphtheria toxin. Exotoxin A.
Describe termination process in protein synthesis in ribosomes.
Once it reaches a Stop codon (UAG,UAA, or UGA) in the mRNA sequence, a protein called Release Factor, binds to the stop codon, hydrolyzing GTP, releasing the polypeptide chain and the ribosome complex falls apart.
How do aminoglycosides work?
It binds to the 30S ribosomes, so it can inhibit bacterial protein synthesis before initiation.
How does Linezolid work?
Binds to 50S before initiation.
How does Chloramphenicol work?
It binds to the 50S that inhibits the peptidyltransferase part, the 23s rRNA.
How do macrolides (Erythromycin, Azithromycin) work?
They bind to the 50S, inhibiting the Translocation step.
How does Clindamycin work?
Binds to the 50S, inhibiting the Translocation step.
How does Lincomycin work?
Binds to the 50S, inhibiting the Translocation step.
How does Streptogramins work?
Binds to the 50S, inhibiting the Translocation step.
What are the 6 antibiotics that target the 50s subunit?
Chloramphenicol. Linezolid. Macrolides. Clindamycin. Lincomycin. Streptogramins.
What are the 2 antibiotics that target 30S subunit?
Tetracyclines. Aminoglycosides.
How do tetracyclines work?
Bind to the 30S, after 50s has been bound, preventing tRNA getting into the A site.
What are the Post-translational modifications that can occur?
Trimming (N-terminal or C-terminal). Covalent modification (Glycosylation, Hydroxylation, Phosphorylation).
What does it mean when they refer to the primary structure of the polypeptide?
The specific sequence of amino acids.
What does it mean when they refer to the secondary structure of the polypeptide?
When they fold into alpha helix or beta pleated sheets.
What extracellular proteins do Fibroblasts make?
Collagen. Fibrillin. Elastin.
What extracellular proteins do Hepatocytes make?
Albumin. Hormone binding globulin. Ferritin. Haptoglobin. Coagulation factors. Fibrinogen.
What extracellular proteins do Plasma cells make?
Immunoglobulins.
What enzyme matches amino acids to tRNA?
Aminoacyl-tRNA synthetase.
Which antibiotics target 30S? Which ones target 50S?
[buy AT 30, CCELLS at 50]
Aminoglycosides, Tetracyclines target 30S. Chloramphenicol, Clindamycin, Erythromycin (macrolides), Lincomyzin, Linezolid, Streptogramins target 50.
What do we need to attach to each tRNA in order to start building polypeptides?
We need to attach an amino acid to each tRNA molecule, AKA “Charge the tRNA”, done by Aminoacyl tRNA synthetase (requires ATP).
