Lecture 4: Translation Flashcards
(42 cards)
in translation of prokaryotic DNA, mRNA is read _____- and protein amino-terminus to carboxy
terminus by convention and physically,
5’ to 3’
what do we need for the initiation of prokaryotic translation?
the two ribosomal subunits (50S and 30S subunits); the
mature mRNA to be translated; the tRNA charged with N-formylmethionine (the
first amino acid in the nascent peptide); guanosine triphosphate (GTP) as a source
of energy, and the three prokaryotic initiation factors IF1, IF2and IF3, which help the
assembly of the initiation complex
The 30S subunit binds to the mRNA template at a purine-rich region (_______) upstream of the AUG initiation codon. The _______ is complementary to a pyrimidine rich region on the 16S rRNA component
of the 30S subunit
the Shine-Dalgarno sequence
what three sites do ribosomes contain?
A (aminoacyl), P,
(pepidyl), and E (exit) sites
Ribosome binds to S-D site (bacteria) in the
________ via complementary
binding on 30S subunit (16s rRNA) and
aligns itself with initiating tRNA in the P site
using the initiation factors to assist in
loading/assembly (IF1 and 2) and
positioning (IF3)
5’ untranslated region
T/F: On rare occasions the ribosome may recognize mRNA without using a
Shine-Dalgarno region (leaderless translation)
true!! but the emchanism is not well understood
explain the elongation process in prokaryotes
new tRNA enters A site, elongation factors (EF-Ts, EF-Tu) react with GTP to cause transpeptidation from polypeptide chain in Psite to Asite, then EF-G translocates polypeptide in A site to P site, tRNA in P site to E site
E site tRNA exits the ribosome and we’re reset!
prokaryotes can transcribe and translate the same gene simultaneously, so they are….
coupled
______ occur when multiple ribosomes translate the same piece of mRNA
polysomes
in _____, transcription is separated by the nuclear envelope
eukaryotes
can we use coupling as a regulatory mechanism?
yes! the trp operon!!
Biosynthetic genes to
make _______
transcribed on an mRNA
that contains two
terminators, one a stem
loop/intrinsic ter near 5’
end of transcript, with
an adjacent leader ORF
containing a lot of trp
codons
tryptophan
Position of ribosome determines whether ________ is used
via “attenuation” mechanism
intrinsic terminator
Low [Trp] slows the ribosome down = _________ = trp genes
transcribed
early ter not used
how do we terminate polypeptide synthesis?
when we reach a stop codon, release factors (which look like tRNA) bind to the A site, peptide is cleaved by peptidyl transferase at the P site
compare and contrast prokaryotic vs eukaryotic translation
70S ribosome vs 80S ribosome
continuouse vs discontinuous
polycistrionic mRNA vs monocistrionic
fMet vs Met
fast vs slower
3 IF’s vs 9 IF’s
formyl group removed after, methionine retained vs. methionine is fully removed
3 RF’s vs single RF (eRF1)
_____ genetic code:
groups of three
consecutive mRNA
nucleotides form
codons that each
correspond to one
amino acid (plus stop
codons)
triplet
how many codons code for amino acids?
61
why do we not have 61 different tRNAs?
genetic code is redundant, codon can determine amino acid but amino acid can NOT determine codon
T/F: most genomes have 30 to 50 different tRNA genes
true
_____ of the codon = wobble position
third base
_______ is the nucelotide of the base hypoxanthine, a deaminated adenine
inosine (I)
inosine found in some tRNAs in the ______
anticodon loop (5’ end)
inosine can base pair with…
C, U, A
