The Mechanism of Translation Flashcards
what does the initiation of translation require?
initiating factors, ribosomal subunits, mRNA, and initiator tRNA
Euk, Initiation:
- AUG start codon specifies?
- initiation factors are called? how many are there?
- the amino acid methionine
- eIFs; there are about a dozen of them
EUK. initiation:
what happens at the beginning of euk. initiation?..
-initiating factor____________ binds to the…?
-the ____ then binds to the…..? along with the _____, including ____?
-resulting complex then binds to the _____ of an ___, recognizing the ________ with the aid of a _______________?
- initiating factor eIF2 (with GTP attached) binds to the initiator methionyl tRNA^Met
- the tRNA then binds to the small ribosomal subunit along with other initiation factors, including eIF1A
- resulting complex then binds to the 5’ end of an mRNA, recognizing the 5’ end cap with the aid of a cap-binding initiating factor; eIF4E
After binding the mRNA:
- ______, along with the _______ in tow, does what?
- the _____ on either side of the ____________ appear to be??
- small ribosomal subunit, along with the initiator tRNA in tow, scans along the mRNA and begins translation at the first AUG triplet it encounters
- the nucleotides on either side of the euk. start codon appear to be involved in its recognition (ex: common start sequence ACCAUGGG
what happens after the tRNA has become base paired with the start codon?
the large ribosomal subunit joins the complex in a rxn facilitated by the hydrolysis of GTP
what does chain elongation involve?
sequential cycles of aminoacyl-tRNA binding, peptide bond formation, and translocation
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: what happens once the initiaion complex has been completed?
-so what is elongation?
a polypeptide chain is synthesized by the successive addition of amino acids in a sequence specified by codons in mRNA
-amino acids are added in sequence to the growing chain (elongation)
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongation stage of polypeptide synthesis involves a repetitive 3 step cycle in which…(3)
- binding of an aminoacyl-tRNA to the ribosome brings a new amino acid into position to be joined to the polypeptide chain
- peptide bond formation links this amino acid to the growing polypeptide, and
- the mRNA is advanced a distance of three nucleotides by the process of tranlocation to bring the next codon into positon for translation
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Binding of Aminoacyl tRNA
-where is the AUG start codon located at the onset of elongation stage? the second codon?
-located at the ribosomal P site and the second codon is located at the A site
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Binding of Aminoacyl tRNA:
when does elongation begin? what does it require to begin?
what happens from now on?
- begins when a tRNA with a anticodon complementary to the second codon binds the A site (1)
- -> this requires two protein elongation factors, EF-Tu and EF-Ts, and is driven by the hydrolysis of GTP
- from now on, every incoming aminoacyl tRNA will bind first to the A site
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Binding of Aminoacyl tRNA
what is the functon of EF-Tu? (along with its bound GTP)
what does the EF-Tu complex promote?
- is to convey the aminoacyl tRNA to the A site of the ribosome
- the binding of all aminoacyl tRNAs to the ribosome except the initiator tRNA, thus ensure that AUG codons located downstream from the start codon do not mistakenly recruit an initiator tRNA to the ribosome
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Binding of Aminoacyl tRNA
-what happens as aminoacyl tRNA is transferred to the ribosome?
- the GTP is hydrolyzed and the EF-Tu-GDP compex is released
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Binding of Aminoacyl tRNA
-what is the role of EF-Ts?
-to regenerate EF-TU-GTP from EF-TU-GDP for the next round of the elongation cycle
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Binding of Aminoacyl tRNA
-what happens if the anticodon for the incoming aminoacyl tRNA is not complementary to the mRNA codon exposed to the A site?
- the aminoacyl tRNA does not bind to the ribosome long enough for GTP hydrolysis to take place
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Peptide Bond Formation:
-what happens once the aminoacyl tRNA is bound to the A site?
peptide bonds form between the amino group of the amino acid at the A site and the carboxyl group of the amino acid at the P site
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Peptide Bond Formation:
- what does the formation of the peptide bond cause?
- is any energy involved?
- causes the growing polypeptide chain to be transferred from the tRNA located at the P site to the tRNA located at the A site
- no ATP or GTP hydrolysis is required for this step
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Translocation:
- After a peptide bond has been formed..
P site contains?
A site contains?
mRNA then?
- P site contains an empty tRNA
- A site contain a peptidyl tRNA (tRNA to which the growing polypeptide is attached)
- mRNA advances to bring the next codon into proper position for translocation
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Translocation:
- during this process of translocation..
- what completes these movements?
the peptidyl tRNA moves from the A site to the P site and the empty tRNA moves from the P site to the E site
-hydrolysis of GTP bound to the EF-G triggers a conformational change that completes these movements
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Translocation:
what happens once the next mRNA codon reaches the A site?
the ribosome is not set to receive the next aminoacyl tRNA
Chain Elongation Involves Sequential Cycles of Aminoacyl-tRNA Binding, Peptide Bond Formation, and Translocation: elongagtion involves 3 repetitive steps: Translocation:
elongation cycle repeats, what happens to the amino terminal of the growing polypeptide?
what assists its foldings?
it passes out of the ribosome thorugh the exit tunnel in the 50S subunit
molecular chaperones assist its folding
Termination of Polypeptide Synthesis is Triggered by?
release factors that recognize stop codons
Termination of Polypeptide Synthesis is Triggered by Release Factors that Recognize Stop Codons :
- how is this done?
- what happens when release factors bind to the stop codons?
- codons are read on the mRNA one after another until a stop codon arrives at the A site
- translating is terminated through release of the completed polypeptide
