Translation Flashcards
1
Q
mRNA is translated in the _ to _ direction and protein synthesis occurs from __ to __.
A
- mRNA translated in the 5’ to 3’ direction
- protein synthesis occurs from N-terminus to C-terminus
2
Q
synonyms
A
codons that specify the same amino acid
3
Q
degeneration of the codon
A
- amino acids specified by more than one codon
- one advantage of the genetic code: degeneracy of the codon minimizes effect of mutations
- many mutations at the third position are silent mutations
4
Q
3 stop codons
A
- UAG (amber)
- UAA (ochre)
- UGA (opal)
5
Q
What happens with mutations at the 2nd codon position?
A
- since purines (R) are all mostly polar and pyrimidines (Y) are all mostly hydrophobic, swapping an R for an R or a Y for a Y produces a smaller effect
- R–Y switch needed for a big change in amino acid
6
Q
open reading frames (ORF)
A
- 3 possible reading frames for mRNA for a total of 6 possible reading frames for DNA
- only one reading frame will encode the protein
- AUG start codon indicates the beginning of ORF
7
Q
frameshift vs. nonframeshift mutations
A
- frameshift: insertion or deletion of 1 or 2 bases; meaning of entire protein is lost
- nonframeshift: an entire codon is inserted or deleted; more similar to original and may have profound or minimal effects
8
Q
tRNA (transfer RNA)
A
- at least one tRNA exists for every amino acid
- make up approx. 15% of the RNA pool
- average 80 nucleotides long
- 4 short segments fold into double helix, forming cloverleaf structure
- further folding into L shape held by H bonds
- have only 13 invariant nucleotides and 8 semi-invariant nucleotides
9
Q
List the parts of the tRNA molecule beginning at the 5’ end.
A
- 5’ end
- acceptor stem
- D (dihydrouridine) stem and D loop
- anticodon stem, anticodon, anticodon loop
- variable loop
- T stem, T loop
- CCA attached to 3’ end
10
Q
isoaccepting tRNAs
A
- tRNA recognizes multiple codons that specify the same amino acid
- e.g. GmAA carries Phe and can recognize both UUC and UUU
11
Q
the wobble hypothesis
A
- pairing at position 1 and 2 are watson-crick but position 3 can be non watson-crick (wobble position)
- wobble position at third position (3’) of codon but first position (5’) on anticodon
- allows the same tRNA to recognize multiple codons that differ in only the wobble position
12
Q
possible wobble anticodon (5’) - codon (3’) base pairs in bacteria
A
(anticodon base can pair with...) - A: U - C: G - G: C or U - U: A or G - I: A or C or U (in eukaryotes the only difference is that U only binds to A and I cannot bind to A)
13
Q
tRNA charging
A
- attachment of the correct amino acid to the 3’ end of tRNA by aminoacyl-tRNA synthetase (aaRS)
- [amino acid + ATP] carboxyl group of amino acid linked to AMP
- [aminoacyl-AMP] adenylated amino acid linked to -OH on sugar of 3’ tRNA
- [aminoacyl-tRNA + AMP] amino acid and tRNA linked by ester linkage
14
Q
aminoacyl-tRNA synthetases (aaRS)
A
- enzymes involved in tRNA charging
- activation of amino acid for protein synthesis
- class I aminoacylates at the 2’–OH
- class II aminoacylates at the 3’–OH
15
Q
aaRS editing
A
- editing capabilities in case of mistakes
- after the amino acid is linked to AMP, aaRS forces it from synthesis site into its second pocket (editing site)
- excludes correct amino acid
- keeps closely related but incorrect amino acid and removes it from AMP/tRNA
- increases tRNA charging accuracy
