What are the three conserved sites in a ribosome? What does it mean for something to be highly conserved?
The aminoacyl/A site: the entry for charged tRNAs
The peptidyl/P site: holds the tRNA to which the polypeptide is attached
Exit/E site: exit of uncharged tRNA
For something to be highly conserved means it is found in all different types of cells
What sequences help initiate translation in bacteria?
The Shine-Delgarno sequence helps the translation initiation complex identify the start codon
What sequences help initiate translation in eukaryotes?
The Kozak sequence helps identify the start codon
What happens when a stop codon is reached?
Termination: release factors (RF) bind to a stop condon in the A site, which results in polypeptide release, RF ejection, and separation of the ribosomal subunits
What are some of the attributes of the genetic code?
universal,
unambiguous and degenerate
Why is it that the genetic code is tolerant to various different types of mutations (even when there is a change in
amino acid)?
There are multiple codons that code for each of the other amino acids, and even if the amino acids change, they would be chemically and “mutationally” close to each other.
What is an iso-accepting tRNA?
tRNAs that are charged with the same amino acid but have different anticodons, one reason why the genetic code is degenerate
Describe the phenomenon of third position wobble.
Some tRNAs can recognize multiple mRNA codons that differ only in their 3rd position
What are some examples of post-translational modifications?
- phosphorylation by kinases (most common, usually activates/deactivates a protein)
- dephosporylation by phosphorylases
- methylation, acetylation, addition of hydroxyl groups
- addition of carb side chains to form a glycoprotein
- proteolysis (cleavage of a polypeptide after translation generates a propeptide – the active form)
- lipidation (targets proteins to membrane-bound organelles, GPI anchors (tether proteins) and S-palmitoylation (addition of hydrophobic chains to tether proteins))
- ubiquitination (marks proteins for degradation)
