Miles - Gene Regulation II/III Flashcards
Missense Mutation
Substitution codes for different amino acid
Nonsense mutation
Substitution codes for stop codon
Silent Mutation
Results in code for same AA
Frame Shift
Worst if not addition/deletion by multiple of 3 Interrupts the entire reading frame
Wobble Pairing
3rd base pair not strict, some overlap–conserves resources Allow G-U, Inosine - U, C, or A
How does tRNA attach AAs?
tRNA requires ATP to be charged with proper AAs by aminoacyl tRNA synthase
Bacterial Initiation
IF-1, IF-2 bind 30S (small) ribosomal subunit.
N-formylmethionyl tRNA joins
IF-2 bound to GTP
50S subunit binds
70S complex formed
NO Poly A Tail
Eukaryotic Initiation
Small ribosomal subunit + initiation tRNA bind initiation codon
Complex associates with large ribosomal subunit
= functional
What is eukaryotic initiation aided by?
Initiation Factors
43S Preinitiation Complex:
IF1, IF1A, IF3 bind 40S
Initiator methionyl-tRNA, IF2 bound to GTP, and IF5 bind to ribosome complex
How is mRNA prepared during eukaryotic initiation?
PABP
IF4F
IF4E
IF4G
IF4B
PABP bind 3’ poly-A tail
IF4F complex bind mRNA
IF4E binds methylguanine 5’ cap
IF4G keeps it all together
IF4B unwinds mRNA
What does the ribosomal scanning of mRNA to find AUG start codon require?
What aids it?
ATP
Kozac sequence
What triggers GTP hydrolysis once start codon is found?
IF5 triggers GTP hydrolysis by IF2
How is eukaryotic initiation regulated?
GTP dependent steps
Two MET codes:
- Initiator (AUG)
Internal sequence MET
What organelle catalyzes peptide bond formation in growing polypeptide chains?
Ribosome
What are the three tRNA binding sites in the ribosome, and what does each do?
A (acceptor) - Holds incoming tRNA
P (peptidyl) - Carries growing peptide chain
E (exit) - Empty tRNA exits
What brings charged tRNA to the ribosome?
EF1alpha (elongation factor)
What induces hydrolysis of ER1alpha/GTP?
Conformational change of ribosome
What enzyme catalyzes the peptide bond formation occuring in the ribosome?
Peptidyltransferas3
What two toxins can inhibit the elongation process?
Diptheria Toxin - inactivates EF-2
Ricin - cleaves adenine residue from 60S subunit and EF-2 can’t bind
How is elongation regulated?
EF-1alpha must be recharged, promoted by EF1BravoGamma
What signals termination? Specific codons:
UAA
UAG
UGA
What aids the breaking of the ribosomal units during termination?
Release Factors (RFs)
What recognizes the stop codon, and what occurs next?
RF-1 recognizes codon, binds RF-3/GTP, and enters the A-site.
Dissociation follows
