Genetics 6 Flashcards
Ionsine
- created by deamination of guanine
- When present in wobble position, tRNA can recognize either U/C in euks or U/C/A in bacteria
Codons that code for the same AA tend to contain…
the same nucleotides at the 1st and 2nd positions- vary at 3rd.
AA Activation
- activated by aminoacyl tRNA synthetase in 2 steps
1) Uses ATP to adenylate AA at OH group, giving AA linked to AMP at carboxy
2) creates aminoacyl-tRNA - *AA is now linked at carboxy group to tRNA by a high energy ester linkage.
Hydrolytic editing
- function of aminoacyl-tRNA synthetase
- wrong AA attached to synthesis site= improper binding to enzyme–> shunted to editing site, AA is hydrolyzed off.
- tRNA synthetase enzymes are specific for each tRNA.
One the AA is attached to tRNA, accuracy is entirely dependent on…
The correct complementation of the codon to the anti-codon.
Kozak/Shine-Dalgarno sequence
Consensus sequences that tell helicase to “start here.”
Elongation Factors
- chaperones
- ensure correct tRNA is binding to codon
EF-Tu/EF-1
Binds GTP, helps tRNA into A site.
- transient binding.
- permanent binding only if pairing is correct.
EF-G/EF-2
- bound to GTP
- Provides energy for shifting ribosomal subunits by hydrolyzing GTP.
- Temporarily binds in A site, dissociates when small subunit rejoins complex.
- binding of EF-G causes tRNAs in A and P site to lean, creating hybrid sites.
Releasing factor
- Binds in the A site when a stop codon is encountered in the mRNA strand.
- Mimics the activity of tRNA
- dissolves elongated peptide off tRNA (water hydrolysis)
- ribosome complex dissociates from mRNA
Riboswitch self cleavage
Riboswitch activates self-cleaving ribozyme activity, leads to degeneration of mRNA, turns translation off.
Riboswitch initiation interference
Riboswitch changes nature of initiation codon, makes it appear in the wrong context. Turns translation off.
