3D- Translation: Synthesis of Proteins Flashcards
What is the general interaction between codons and anticodons?
each tRNA molecule contains an anticodon and binds covalently a specific amino acid at its 3’ end.
the codon and the anticodon must be complementary, therefore each codon is specific for 1 anticodon and thus 1 amino acid
What does it mean when we say the genetic code is “degenerate”?
I means that each amino acid may have more than 1 codon
What does it mean when we say the genetic code is “unambiguous”?
Each codon specifies only 1 amino acid
Where is the “wobble position” and what does it do?
It is on the 5’ of the anticodon (on the tRNA) and correlates with the 3’ codon
hypoxanthane (I) is the unusual base that is at the wobble position, and pairs with U C or A on the 3’ codon.
Though it is variable, the other 2 codons maintain the degeneracy and unamibuousity of the genetic code
What does it mean when we say the genetic code is “non-overlapping?”
It means the mRNA doesnt contain puntuation to separate 1 codon from the next and the codons do not overlap
each nucleotide is read only once
How universal is the genetic code?
Extremely universal- all organisms use the same genetic code, with some rare exceptions
the only exception is in human mitochondrial mRNA, which UGA codes for tryptophan instead of serving as a stop codon, AUA codes for Met instead of Ile, and CUA codes for Thr instead of Leu
What are point mutations?
Name the 3 types
They occur when only 1 base in DNA is altered, producing a change in a single base of an mRNA codon
there are 3 types:
- Silent- they do not affect the AA sequence because the point mutation changed the codon but not the AA that it was coding for.
- Missense- one AA in the protein is changed. This can be small or large effects.
- Nonsense- the change is from a AA codon to a stop codon. Big change in AA chain.
What are insertion and deletion mutations?
An insertion is when 1 or more nucleotides are added to DNA. If the insertion doesnt generate a stop codon, a protein with more amino acids than normal could be produced.
When 1 or more nucleotides are removed from the DNA, the mutation is a deletion.
BOTH ARE FRAMESHIFT MUTATIONS
What occurs during the initiation phase of translation?
The 5’ end of the mRNA with the 5’ cap bind to the small 40s subunit –> these and initiation factors hold it in place –> eIF3 keeps large subunit from binding –> charged tRNA with Met comes and binds with AUG –> large subunit comes and tRNA is in P site
What occurs during the elongation phase of translation?
After the P site is filled with the Met-charged tRNA that binds to AUG on the codon –> the next tRNA with the AA arrives and corresponds with the appropriate codon in the A site –> peptide bond forms between the 2 amino acids on the tRNA’s –> the 2 shift into the E and P sites –> tRNA that had Met leaves –> continue this process until you arrive at a STOP codon
What occurs during the termination phase of translation?
when the UGA codon arrives –> release factors bind to the ribosome –> peptide is released from the ribosome
What are 3 posttranslational modifications to the newly formed peptide chain?
- the initial Met is removed by specific proteases- Met isnt the N-terminal amino acid for all proteins
- Specific cleavages may convert the peptide into more active formes (like the cleavage of isulin)
- amino acid residues can be modified by the addition of various functional groups- methylation, glycosylation, fatty acid addition, phosphorylation, etc.
- Describe the mechanisms used for protein targeting in the cell including chaperone-mediated and vesicle-mediated pathways
- Describe the relationship between defects in phosphotransferase activity and the lysosomal storage disorder I-cell disease
i. The phosphotransferase in the golgi transfers a phosphate to mannose residues on specific N-linked glycoproteins, which serves as a marker for them to be targeted to lysosomes within the cell. Without the marker the proteins are instead excreted outside the cell.
ii. Lysosomes cant function without these proteins buildup of these substances occurs within lysosomes because they can’t be degreaded results in inclusion cells or “I cells”
What is the mechanism of action of streptomycin?
i. Binds to the 16s rRNA of the 30s subunit, prevents initiation by blocking the formyl-methionyl-tRNA binding.
ii. Since translation cannot occur, the bacterium dies.
