4-2: Translation Flashcards
What are the two rare AA?
Selenocysteine, pyrrolysine
What are protein domains
Structural or functional segments of a protein
What is the helix-turn-helix (HTH)
Protein domain that binds DNA, found in DNA binding regulatory proteins. Found in hundreds of proteins of the Salmonella genome.
What structures are involved in tRNA
70-95 bases long, extensive structures that often contain modified bases (eg. mG)
What are tRNA synthetases? What do they do?
Add cognate amino acid to CCA at 3’ end of tRNA to “charge” them
What are the translation start codons
Encode for first aa of ORF
Usually AUG (83%)
Can also be GUG, UUG
What is the amino acid that the start codon is translated to in bacteria?
N-formylmethionine (fMet)
Does AUG always encode fMet?
No, unless it is start codon it encodes normal Met
What are the three stop codons
UAA, UGA, UAG
The prokaryotic ribosome is made up of what subunits?
- 30S (small) subunit
- 50S (large) subunit
What is the size of the prokaryotic ribosome in Svedberg units?
70S ribosome
What are ribosomal subunits made of?
rRNA and ribosomal proteins
What are the E coli 30S and 50S ribosome subunits made of
30S = 16S rRNA, 21 proteins
50S = 5S/23S rRNA, 31 proteins
What carries out the main function of ribosome
rRNA - responsible for catalyzing peptide bond formation
How is translation initiated
16S rRNA in 30S subunit binds to the ribosomal binding site that is correctly spaced from the start codon AUG
30S binds RBS, fMet tRNA binds AUG
50S subunit recruited using GTP to form the full 70S ribosome
The ribosomal binding site (RBS) is also known as what?
Shine-Dalgarno sequence
What are the 3 tRNA binding sites of the ribosome
- A (aminoacyl) site
- P (peptidyl) site
- E (exit) site
What is the A site
New charged tRNA’s enter, recognize codon needing aa
Growing peptide from P site transfers to aa in A site
What is the E site
uncharged tRNA exits
When does translation end
Stop codon encountered, release factor protein binds, releasing peptide and mRNA. Ribosome dissociates
What is used as the energy source in translation?
GTP
What are polysomes?
Multiple ribosomes on a single mRNA simultaneously translating
When can polysomes form?
When the 5’ end of RNA in an ORF is translated and freed up
What is transcription/translation coupling
RNA is being translated as it is still being transcribed
How is eukaryotic translation different from bacterial?
No coupling of translation and transcription
Initiation step different (5’ cap recognized)
Ribosome larger: 40S + 60S = 80S
what are chaperones
Proteins that help other proteins adopt their properly folded/active states
Functions of chaperones
Initial folding, re-folding denatured proteins, helping subunits in multimeric proteins come together, RNA folding
Energy source of chaperons?
ATP hydrolysis
What can activate chaperones?
High or low temperatures (eg. heat chock proteins, cold shock proteins)
How do proteins get out of the cytoplasm into different locations
Translocase systems
Where is the signal sequence found?
N terminus
What are the two secretion systems
Sec secretion system
Twin arginine translocase (tat)
What does the tat pathway do
Secretes pre-folded proteins across membrane
What does the sec secretion do
Recognizes signal in first 20 aa, translocates unfolded protein
What are the two sec pathways
SecA and SRP
What does the SecA pathway do
Pass unfolded proteins across cytoplasmic membrane
What does the SRP sec pathway do
Protein recognized by signal recognition particle and inserted into membrane
What do both SecA and SRP do?
Pass unfolded protein through Sec YEG translocon
Require ATP
Cleave the signal sequence following translocation
