Translation Elongation and Termination Flashcards
What are the first two steps for the starting condition in elongation?
The small and large subunits come together to form a ribosome
The mRNA is bound to the small subunit and the start codon is positioned next to the P site
What are the 3rd and 4th steps for the starting of elongation?
The initiator tRNA is located in the P site and is paired with the start codon. The first amino acid in the polypeptide is the amino acid at the N terminus.
The second codon is positioned next to the A site, and the A site is empty
What are the steps in each cycle for elongation?
- Entry of an aminoacyl-tRNA into the A site
- Peptide bond formation
- Translocation
What are the three different proteins required for elongation?
eEF1 Alpha
eEF1 Beta Gamma
eEf2
What is the 1st step of an elongation cycle?
The attachment of an aminoacyl-tRNA to the A site of the ribosome
What is the attachment of an aminoacyl-tRNA to the A site of the ribosome aided by?
eEF1 Alpha and eEf1 Beta Gamma
How does aminoacyl-tRNA enter the A site?
It enters in such as way that allows pairing between its anticodon and the second codon
What will the amino acid attached to the aminoacyl-tRNA become?
It will become the second amino acid in the polypeptide
What is the 2nd step in the elongation cycle?
A peptide bond is formed between the methionine in the P site and the amino acid in the A site
What occurs simultaneously as a peptide bond is formed between the P and A site?
The covalent bond linking the methionine to the tRNA in the P site is broken
The tRNA in the P site is now empty
When the P site is empty, what happens to the aminoacyl-tRNA in the A site?
It is now linked to two amino acids
The tRNA is attached to the polypeptide and is now called the peptidyl-tRNA
What enzyme catalyzes the peptide bond formation and transfer of amino acids to the peptidyl-tRNA?
Peptidyl transferase
Where is peptidyl transferase located?
In the large subunit
It is the 28S rRNA
What is the 3rd step in elongation?
Translocation
What eEF is required for translocation?
eEF2
What happens to the ribosome during translocation?
The ribosome shifts its position slightly in relation to the mRNA
The star codon, which was next to the P site, is now next to the E site, and codon 2, which was next to the A site, is now next to the P site, and codon 3 is now positioned next to the A site
(BASICALLY EVERYTHING MOVES ONE SPACE)
What happens to tRNAs during translocation?
The empty tRNA is shifted from the P site to the E site, the peptidyl-tRNA is shifted from the A site to the P site, and the A site is now open for another aminoacyl-tRNA to enter.
The cycle can then repeat itself.
(once again, everything moves one)
In termination, what are the stop codons?
Stop codons are translation termination signals
The codons are UGA, UAA, or UAG
When does termination begin?
When one of the three stop codons is positioned adjacent to the A site of the ribosome
True/False, there is only one stop codon present in mRNA.
True
It is the first UGA, UAA, or UAG encountered by the ribosome as it moves along the mRNA
What base sequence lies beyond the stop codon?
3’ UTR
What protein does termination of translation require? What does it do?
eRF1
eRF1 can attach to any one of the three stop codons
What happens when a stop codon is positioned next to the A site?
The stop codon is recognized by eRF1, attaching to the stop codon
What does eRF1 interact with? What does it cause?
eRF1 interacts with the peptidyl transferase of the ribosome, causing the peptidyl transferase to cleave the bond between the peptidyl tRNA and the polypeptide
What is the result of the cleaved bond between the peptidyl tRNA and the polypeptide?
It results in the release of the polypeptide from the tRNA and detachment of the polypeptide and the empty tRNA from the ribosome
What happens at the end of the translation process?
eRF1, the small and large subunits, and the mRNA all detach from one another
