Translation Flashcards
Info encoded in DNA is transferred to ________________ and then decoded by the _______________ to produce proteins
mRNA
ribosome
What are the major molecules involved in translation?
messenger RNA
transfer RNA
ribosomes
enzymes, other factors, energy sources
mRNA transcript carries a series of codons that interact with the anticodons of ____________________ so that a corresponding series of amino acids is incorporated into a polypeptide chain.
aminoacyl-tRNA
What structure provides the environment for controlling he interaction between mRNA and aminoacyl-tRNA and the full range of activities for all translation steps?
ribosome
ribosome behaves like a small migrating factory that travels along the mRNA template, engaging in rapid cycles of _______________ to build polypeptide
peptide bond cycles
_______________ shoot into the ribosome at an incredibly fast rate to deposit amino acids, and elongation factor proteins cyclically associate with and dissociate from the ribosome.
Aminoacyl-tRNAs
adapter molecule that translates genetic information into protein sequence by delivering amino acids to the protein synthesis machinery during translation
tRNA
each tRNA is specific to carry what?
one of the 20 amino acids
What is the structure of tRNA?
cloverleaf shape with 4 stem loops
part of the tRNA where the amino acid is attached
acceptor stem
part of the tRNA that contains the anticodon triplet that recognizes the complementary codons on mRNA during protein synthesis
anticodon loop
deoxyuridine stem loop
d-arm
TYC stem loop
t-arm
variable loop
v-loop
made up of 2 subunits that lock around the mRNA and travel along the length of the mRNA molecule reading each 3-letter codon
ribosomes
serves as a docking station for the tRNA that matches the sequence of bases on the mRNA
ribosomes
A site
binding site for the first amino acid
P site
binding site for the peptidyl tRNA
E site
binding site for the uncharged tRNA; exit site
Svedburg units for prokaryotic ribosomes
70S
50S - 30S
Svedburg units for eukaryotic ribosomes
80S
60S - 40S
a slow step that determines the rate at which an mRNA is translated
initiation
the most rapid step in translation
elongation
protein synthesis begins the the formation of an __________________
initiation complex
what are the components involved in the initiation complex in E.coli?
30S ribosome
mRNA template
3 initiation factors
special initiator tRNA (tRNAmetf)
The 30S subunit binds to the mRNA template at a purine-rich region called the __________________________ upstream of the AUG initiation codon.
Shine-Dalgarno sequence (AGGAGG)
What codons are recognized by tRNA metf
AUG or GUG
Summarize initiation for bacteria.
The 30S subunit, initiation factors, and initiator fMet-tRNA bind to the mRNA to form the pre-initiation complex, which then recruits the 50S subunit to start translation elongation.
How does bacterial elongation start?
It starts when the fMet-tRNA enters the P site; this causes a conformational change which opens the A site for the new aminoacyl-tRNA to bind
movement of tRNA from A to P to E is induced by ______________ that advance the ribosome by three bases in the 3’ direction
conformational changes
Where does the energy for each step along the ribosome come from?
elongation factors that hydrolyze GTP
required for binding of a new aminoacyl-tRNA to the A site and its translocation to the P site after formation of the peptide bond
GTP energy
What type of bonds form between the amino group of the amino acid attached to the A-site and the carboxyl group of the amino acid attached to the P-site
peptide
RNA-based enzyme that is integrated into the 50 S subunit and catalyzes the formation of each peptide bond
peptidyl transferase
What happens after the peptide bond forms?
the A-site moves to the P-site and the P-site is empty and moves to the E-site and is expelled from the ribosome
What are the nonsense codons that signal termination?
UAA
UAG
UGA
What codons do the bacterial RF1 recognize?
UAA and UAG
What codons do the bacterial RF2 recognize?
UAA and UGA
During termination, the release factors instruct peptidyl transferase to add _____________ to the carboxyl end of the P-site amino acid, causing the amino acid to detach and the new protein released
a water molecule
What happens first in eukaryotic initiation?
the small subunits recognize the 5’cap at the end of the mRNA and then move to the initiation site
what sequence in eukaryotes allows for the proteins to bind the small unit and hold the mRNA in place?
Kozak sequence (ACCCAUGG)
Do prokaryotes or eukaryotes have more initiation factors?
eukaryotes
associated with 40S subunit and plays a role in keeping the large 60S subunit from prematurely binding
eIF3
together with met-tRNA, eIF3, eIF1, and eIF1A binds to the 40S to form the 43S preinitiation complex
eIF2
eIF4A, EIF4B, eIF4E, and eIF4G bind to the 5’ end of the mRNA to form the _____________________________
cap-binding complex
What does the cap-binding complex do?
it associates with 3’ end of mRNA via eIF4G which interacts with PolyA binding protein (PABP)
what does the 43S complex do?
It binds the initiation factors at the ‘ end of the mRNA and scans for initiation codon
Which initiation factor brings Met-tRNAi ti the P-site of the small ribosomal subunit?
eIF2
What hydrolyzes GTP and signals for the dissociation of several factors from the small subunit leading to association of the large subunit?
Met-charged initiator tRNA
What two elongation factors does eukaryotic elongation depend on?
EF-1 and EF-2
During eukaryotic elongation, each amino acid is added to the polypeptide chain in what 3 steps?
1) positioning the correct aminoacyl-tRNA
2)forming the peptide bond
3) shifting the mRNA by one codon relative to the ribosome
what is different about eukaryotic termination?
a universal release factor (eRF1) recognizes all 3 stop codons
