The Genetic Code and Translation Flashcards
Lectures 8 & 9
does mRNA last longer in eukaryotes or prokaryotes?
eukaryotes, since transcription and translation occur simultaneously in prokaryotes
which researchers did work on the collinearity hypothesis?
Beadle and Tatum: one gene encoded one discrete polypeptide
Yanofsky: nucleotide triplets correspond to sequence of AAs
what joins amino acids?
peptide bonds (dehydration reaction)
carboxyl group joins amino group
what are the four structures of proteins
primary: linear sequence of AAs
secondary structure: spacial organization, by H-bonds
tertiary structure: interactions between R groups, folded around secondary structure
quaternary structure: interactions between polypeptides
why is the genetic code degenerate?
flexibility in 3rd codon position (1st anticodon)
WOBBLE –> two codes can designate the same AA
what is inosine?
RARE BASE in tRNA
derivative of adenine/guanine can bind with C, U, or A –> more flexibility
what is the wobble hypothesis?
nonstandard pairings can take place at the 3rd codon position
what macromolecules are involved in translation?
RIBOSOMES –> made up of many proteins and rRNAs
AMINO ACID ACTIVATING ENZYMES –> catalyze reaction
tRNA molecules
SOLUBLE PROTEINS
what is aminoacyl tRNA synthetase?
“charges”/binds tRNA with the amino acid it codes for
AA reacts with ATP
AMP binds to AA, PPi leaves
AMP removed, tRNA added to -OH group of AA
describe initiation in prokaryotes
IF3 binds to small subunit, preventing large subunit from binding
small subunit attaches to mRNA
tRNA charged with f-MET forms a complex with IF2 and GTP
complex binds to initiation codon while F1 joins the small subunit
IFs disassociate, GTP hydrolyzed to GDP
large subunit joins to create 70S complex
how does initiation differ in EUKARYOTES?
MET not f-MET
no shine-dalgarno sequence –> KOZAK sequence instead
ribosome initiation complex scans for the first AUG initiation codon
poly a tail and 5’ cap interact via the CAP BINDING PROTEIN COMPLEX
describe elongation
fMET occupies the P site of tRNA
incoming charged tRNA forms a complex with GTP and Tu (an elongation factor)
tRNA complex enters the A site
complex moves to the P site when another complex comes in
what direction does the polypeptide grow in
N-terminal to C-termina;
what direction does the ribosome move down the mRNA
5’ to 3’
describe the process of termination
stop codon enters the A-site
no tRNAs bind to the stop codon
release factor binds to A-site
cleave polypeptide chain from tRNA, releasing the chain
