translation Flashcards
the process of protein synthesis is called ____________, and it occurs on an enzyme complex called the ___________.
translation; ribosome
codon
series of three bases specifying one amino acid in a protein; code read 5’->3’ and protein is synthesized from amino- (N-) to the carboxyl- (C-) terminus
open reading frame (ORF)
encodes the primary sequence of only one protein
- begins with start codon (AUG) and ends at a stop codon
- ORF is continuous series of codons
- genetic code is non-overlapping
the code is degenerate which means
most amino acids are encoded by more than one codon
- leu, arg, ser have 6 codons each
- met and trp only have 1
mutation
accidental change in a DNA sequence. it may affect the sequence of a protein encoded in an mRNA
nonsense mutation
introduces a stop codon; normally results in a nonfunctional protein
missense mutation
replaces one amino acid codon with another; protein effects depend on many things
silent mutation
changes the DNA sequence without altering the encoded protein
frameshift mutations
caused by an insertion or a deletion within a coding sequence, but the change is not a multiple of 3 bases
- often leads to an early stop codon truncating a protein
- mutations that affect RNA splicing often generate frameshifts
what is the most frequent mutation associated with cystic fibrosis?
an in-frame deletion of UUC (phe) codon in CFTR
_______ deliver aminos acids to the ribosome
- cloverleaf secondary structure
- many modified bases
- have AAs bound at 3’ end
tRNAs
the primary determinants for amino acid selection are _______________________________.
- a tRNA _______ base pairs to a mRNA codon in an antiparallel orientation.
bases #1 and #2 of the mRNA codon; anticodon
the third base of many codons pairs loosely, or wobbles, with the corresponding base of its anticodon. this base is known as the ______________
wobble base
tRNAs can bind to multiple different codons that encode an amino acid because…
of the leniency at the wobble position
- 32 tRNAs needed to translate all codons
non canonical base pairs are allowed at wobble bases (codon #3 to anticodon #1)
anticodon U=A or U=G
anticodon G-=C or G=U
anticodon inosinate (I) I=A or I=U or I=C
___________________ read variant sequence elements to select the correct tRNA to be charged with a particular amino acid
aminoacyl-tRNA synthetases
the _____________ dictate 3D structure of tRNAs
invariant
each amino acid requires its own ___________________
aminoacyl-tRNA synthetase
ribosomes are __________ and only ___________ by wieight
65% rRNA; 35% protein
prokaryotes have one ribosome, ______________
the 70S ribosome
eukaryotic cells have at least two:
80S ribosomes in the cytoplasm and endoplasmic reticulum
mitochondria have a 55S ribosome
ribosomes have 3 tRNA binding sites:
A site for aminoacyl tRNA ( where charged tRNA enters)
P site for peptidyl tRNA (attached to growing peptide)
E site for empty (where uncharged tRNA goes to exit)
polysomes
multiple ribosomes bound to a single mRNA
______________ act on the _____________.
- _______ blocks premature tRNA binding at the A site
-_______ blocks premature binding of the 50S subunit
-mRNA binds to the 30S subunit by base pairing between the 16S rRNA and the Shine-Dalgarno sequence. (as a result, the AUG start codon is arranged into the P-site)
initiation factors; 30S ribosomal unit; IF-1; IF-3
the shine-dalgarno or ribosome binding sequence (RBS) is …
8-13 nt purine-rich element in mRNA where ribosomes bind to initiate translation
although _____ is always the first amino acid in a prokaryotic protein, the second and each subsequent amino acids can be any one of the 20
fMet
_______ binds charged initiator fMet-tRNA and escorts it into the P site
IF-2-GTP
IF-2 hydrolyzes the GTP, resulting in ….
dissociation of all IFs
the __________ binds forming the complete ___________.
- the complex is now complete
- ____________________:
- A site is vacant
- P site has fMet-tRNA
- E site is vacant
50S subunit; 70S ribosome; translation initiaton complex
_________________ act on the 70S ribosome
elongation factors (EFs)
___________ binds an __________ in the cytoplasm and delivers this charged tRNA to the ribosomal A site.
- base pairing occurs between the aminoacyl-tRNA anticodon and the second codon in the mRNA.
- tetracyclines bind to the 30S subunit blocking aminoacyl-tRNA entry into the A site
EF-Tu-GTP; amino acyl-tRNA
____________ hydrolyzes GTP-> GDP + Pi and exits
- A site has an aminoacyl-tRNA
- P site contains fMet-tRNA
- E site remains vacant
EF-Tu-GTP
EF-Tu-GDP is recycled to EF-Tu-GTP by _________
EF-Ts
the ribosome is a ___________.
- the free amino group on the acyl-tRNA in the A site attacks fMet-tRNA in the P site
- fMet is transferred to nascent chain in the A site forming the first peptide bond
peptidyl transferase
_____________ binds 50S subunit blocking peptidyl transferase activity
chloramphenicol
the ________________ moves the mRNA through the cleft in the ribosome
EF-G GTP translocase
___________ binds near the A site
- GTP-> GDP shifts ribosome down one codon on the mRNA
- A site is again vacant
- P site contains dipeptidyl-tRNA
- E site has an uncharged tRNA that quickly dissociates
- _____________ binds to the 50S ribosomal subunit rRNA and blocks the binding site for EF-G
EF-G GTP; erythromycin
___________ changes shape of rRNA in 30S subunit, causing ribosome to misread mRNA
streptomycin
at a stop codon, the ribosome …
pauses and waits for a new charged tRNA
a ___________ recognizes the stop codon and binds to the A site (essentially tricks ribosome into thinking its a charged tRNA)
- ____________ activate peptidyl-transferase hydrolyzing the peptidyl-tRNA bond terminating translation
release factor (RF)
_____________ and ______ dissociate the complex
______ rebinds to 30S subunit
ribosome recycling factor (RRF) and EF-G; IF-3
how is eukaryotic translation different from prokaryotic translation?
mRNAs are synthesized and RNA processed in the nucleus
- mRNA is transferred to the cytoplasm where it may be intercepted by miRNA-RISC
the __________ carries out translation. (eukaryotes)
80S ribosome
eurkaryotic translation initiation complex
- ____ brings charged Met-tRNA to the _____________ before the mRNA
- ____ complex binds to the mRNA 5’ cap and brings it to the 40S
- the ribosome scans the mRNA 5’->3’ to locate the AUG within a ______________
- ___________ binds to complete the _____________
eIF2; 40S subunit; eIF4; Kozak sequence; 60S subunit; 80S ribosome
