26 - Transfer RNA Flashcards
585-590
What is Crick’s adaptor hypothesis? How many adaptors are needed for this hypothesis? What is the adaptor in protein synthesis?
An amino acid is carried to the template by an adaptor molecule, and that the adaptor is the part which actually fits onto the RNA.
20 twenty adaptors for this hypothesis, one for each amino acid.
tRNA (transfer RNA) is the adaptor in protein synthesis
What is the amino acid attachment site on tRNA?
3’ terminal A residue
What is the template recognition site called on tRNA?
The anticodon
What proved the adaptor hypothesis?
- A Cysteine tRNA was attached to cysteine
- Raney nickel was used to convert cysteine to alanine
- When this complex was treated with a protein synthesizing system, alanine residues were incorporated into positions normally occupied by Cys residues
This proved that tRNAs are adapted to each amino acids
Where are invariant and highly conserved regions on tRNA? (4)
- Surrounding anticodon loop
- In D loop
- In ΤΨC loop
- In acceptor stem
Where are variable regions in tRNA? (2)
- D loop
- Variable loop
What is type of uracil is found in the ΤΨC loop of tRNA?
Ψ (pseudouridine, aka 5-ribosyluracil)
What type of uracil is found in the D loop of tRNA?
dihydrouridine
What are two types of unusual base pairings in tRNA?
- Non-standard base pair matches (eg. G=C)
- Base triple interactions (eg. pyridine bound to pyrimidine bound to pyrimidine)
What do numbers following bases show in yeast tRNA (eg. A9)?
The position in the sequence of the yeast tRNA
A9: Adenosine at position 9
Which type of tRNA structure is variable and which is highly similar?
Variable: secondary structure
Conserved: tertiary structure (L-shaped tertiary structure)
What is the critical distance in tertiary tRNA structure?
The distance between the anticodon at one end of the L and the amino acid attached to the 3’ terminus at the other end of the L
What is the structure of the amino acid site of tRNA?
An 7 base long acceptor stem followed by:
CCA-OH-3’
The amino acid binds to the 3’ adenine residue
Is peptide bond formation thermodynamically favourable or unfavourable? Why?
Thermodynamically unfavourable because it involves the elimination of a water molecule
How is the carboxyl (-COOH) group of the precursor amino acid activated? Are there intermediates?
Conversion to an acid anhydride by aminoacyl-tRNA synthetase (ARS)
There is a aminoacyl-adenylate (aminoacyl-AMP) intermediate (mixed anhydride)