Lecture 2 Flashcards
(13 cards)
What joins the amino acid to its corresponding tRNA?
Aminoacyl-tRNA synthetase
Structure of tRNA?
Clover leaf secondary structure
75-80 nucleotides
Conformation, 3D shape -held together by complementary base pairing within own sequence
3’ end is amino acid attachment site -binds covalently
Mid point -anticodon loop -group of 3 bases called the anticodon -is the site of complementary base pairing with mRNA
How does the enzyme aminoacyl-tRNA synthesise reaction take place?
Each enzyme is specific from one amino acid and its corresponding tRNA
Enzyme has a 3 part active site -recognises three smaller molecules, a specific amino acid, ATP and a specific tRNA.
ATP hydrolysed to AMP -considerable energy to make the bond.
A site of a ribosome?
Where the charged tRNA anticodon binds to the mRNA codon -thus lining up the correct amino acid to be added to the growing polypeptide chain.
What is the recognition sequence on mRNA called?
Shine-Dalgarno sequence -upstream (towards 5’ end) of the start codon that starts translation
Initiation
Small subunit binds to methionyl charged tRNA.
Small subunit binds to mRNA at recognition sequence -Shine-Dalgarno upstream.
Travels along the 5’ untranslated end of mRNA until it reaches AUG codon -scanning.
Start codon (AUG) binds to tRNA anticodon.
Large subunit of ribosome binds -the first amino acid is sitting in the P site.
Elongation
Charge tRNA with anticodon complementary to second codon of mRNA enters A site
Large subunit catalyses 2 reaction: breaks bond between tRNA in the P site and its amino acid
Catalyses the formation of a peptide bond between that amino acid and the one attached to tRNA in the A site
Ribosome moves one codon along the RNA in the 5’ to 3’ direction
First tRNA now in the E site -dissociates from the ribosome
Second tRNA now bearing the dipeptide is in the P site
What is the road of elongation factors?
Puts energy into the system by hydrolysing GTP
Role of EF1/ EF-Tu?
Carries aminoacyl-tRNA to the ribosome and also binds GTP.
Base pairing correct -hydrolyses GTP to GDP and phosphate and releases the aminoacyl-tRNA
What is the role of EF2?/ EF-G
Has GTP bound binds to the A site
Hydrolyses GTP and helps reset the ribosome ready for the next aminoacyl-tRNA -slides and resets.
What are the 3 stop codons?
UAA, UAG and UGA
What do the stop codons bind?
Bind a protein release factor.
What happens when a stop codon enters the A site?
Release factor binds to A site.
With the help of the release factor peptidyl-tRNA bond is hydrolysed
This breaks the bond between tRNA and the last amino acid in the protein.
Releases the new protein which separates from the ribosome.
Ribosome dissociates into large and small subunits.
