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23 Cards in this Set
- Front
- Back
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1. Where does protein synthesis occur?
What role does tRNA play? |
In cytoplasm on protein-RNA complexes (ribosomes)
Serve as adapters and carry amino acids to the ribosomes At special sites on the ribosome three bases on the tRNA (anticodons) base pair with sequences on the mRNA |
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2. What is the genetic code?
What is a codon? What are 5 characteristics of the genetic code? |
3 letter code
Three base sequence in mRNA that specifies an amino acid 1. Non-overlapping 2. Non-punctuated 3. Not ambiguous 4. Degenerate (more than one codon to specify each AA) |
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3. What is the start codon?
What do the "nonsense codons" code for? What is an "open reading frame"? |
AUG (methionine)
Stops signals (UAA, UAG, UGA) Series of 50 or more codones that are not interrupted by a stop codon |
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4. Why is the genetic code degenerate?
How do you read mRNA? |
Have degeneracy to minimize effects of mutations
Start with 5' end and first AUG (methionine) |
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5. What is the reading frame?
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Way of reading mRNA
Correct reading frame begins with AUG **every protein begins with methionine but may not have it as the first due to modifications |
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6. What are the 5 steps in protein synthesis?
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1. Activation of amino acids
2. Initiation of protein synthesis 3. Elongation of the polypeptide 4. Termination and release of the protein 5. Folding and processing of the protein |
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7. Where does the activation of amino acids begin?
What does it mean to say the the tRNA is "charged"? |
Cytosol
tRNA with anticodon corresponding to a codon in the mRNA has the proper AA attached to it by an enzyme called aminacyl tRNA synthetase |
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8. What is expended to charge the tRNA?
Once the tRNA is charged what happens? |
Two high energy phosphate bonds
Irreversible It uses its anticodon to add AA to growing polypeptide chain |
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9. Where does initiation begin?
What is needed to start translation? Where does translation begin? |
Amino terminal
Eukaryotic initiation factor (eIF) -3 in bacteria -12 in eukaryotes Begins at the first AUG in the mRNA |
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10. What roles do IFs play?
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Help assemble ribosome and tRNA
**They require energy |
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11. What is the "Shine-Delgarno sequence"?
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A specific sequence in the mRNA of prokaryotes that facilitates the recognition of the starting AUG initiation codon
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12. What uses the shine delgarno and how?
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The 30s subunit
Used to align the AUG codon with the P site on the ribosome |
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13. When is initiation complete?
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When the 50s subunit of the ribosome binds to the complex
GTP is hydrolyzed to GDP and initiation proteins are released |
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14. Instead of the shine delgarno what do eukaryote cells have?
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5' MeF
5' CAP line up ribosome on mRNA eIF is cap binding protein |
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15. How does elongation of the polypetide occur?
Four steps... |
1. Subsequent addition of AA is accomplished by tRNAs bindng at a neighboring site, "A" (acceptor) site
2. Elongation factors (proteins) assist -requires hydrolysis of GTP 3. Peptide bond is formed between AAs bound to tRNAs that occupy P and S sites 4. Ribosome translocates one codon toward the 3' end of RNA |
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16. What does peptidyl transferase do?
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Enzyme that forms the peptide bond between the AAs in the P and A site
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17. Where are the two amino acids attached?
What does translocation require? |
Attached to P site
1. Protein EF2 (translocase) 2. GTP (hydrolized) |
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18. When does elongation stop?
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When a stop codon is reached (UAA, UAG, UGA)
When a stop codon occupies A site, the last peptidyl-tRNA bond is hydrolyzed and free polypeptide is released |
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19. What happens to the ribosome?
What does termination require? |
Dissociates
Release Factor |
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20. How do antibiotics affect protein synthesis?
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Attack Ribosome (very vulnerable targets in bacteria)
Bacteria 70s subunit has structural differences from eukaryotic 80s subint |
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21. What are some examples of how antibiotics block protein synthesis?
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1. Block propagation
2. Block peptidyl tranferase and prevent binding of aminoacyl tRNA (chloramphenical) 3. Prevent translocation (erythromycin) 4. Inhibit initiation step (assembly of ribosome) - streptomycin 30s subunit 5. Prevent aminoacyl tRNA from binding (tetracycline 30s subunit) |
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22. What causes the proteins to fold?
What do proteins use to help with folding and why? |
AA presents reactive surfaces especially hydrophobic surfaces to one another causing folding
Chaperones -protein molecules that prevent improper folding |
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23. How do chaperones prevent improper folding?
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1. Hsp (heat shock protein)
2. Bind to end of protein prevent improper folding and degradation 3. Form barrel like structures in which protein folds and unfolds until it reaches lowest energy state |
