BGM1002/L18 Translation I Flashcards
Give the 4 main features of the genetic code?
Triplet
Non-overlapping
Degenerate/redundant
Universal
How many combinations does a triplet code allow?
4^3
64
How many stop codons are there?
3
How many codons specify amino acids?
61
How many start codons are there?
1 (MET)
In what organism is the CUG codon reassigned from Leu to Ser?
Candida albicans (yeast)
How many species of tRNA exist in E. coli?
46
Describe the primary structure of tRNA. (3)
Small - 70-90 nucleotides
Have 5’ monophosphate (rather than 5’ triphosphate)
Contain modified bases
Name the 4 modified bases that exist in tRNA.
Ribothymidine
Pseudouridine
Dihydrouridine
Inosine
Describe the secondary structure of tRNA. (5)
D-loop (contains dihydrouridine)
T-loop (contains pseudouridine)
Variable arm
Anti-codon loop
Amino acid acceptor site
What is the 3’ terminal nucleotide sequence in tRNA?
-CCA
What are tRNAs joined to amino acids called?
Aminoacyl tRNA
Charged tRNA
What type of enzymes catalyse aminoacylation of tRNAs?
tRNA synthetases
Describe aminoacylation of tRNA. (3)
AMP added to carboxyl group of amino acid
High energy intermediate formed - aminoacyl adenylate
Aminoacyl adenylate reacts with appropriate uncharged tRNA
Which hydroxyl are amino acids joined to on tRNA?
2’ or 3’
Once joined, two species can interconvert
Name the 2 classes of tRNA synthetases.
Class I
Class II
Name the differences between each class of tRNA synthetases. (2)
Each contains enzymes specific for 10/20 amino acids
Bind different faces of tRNA molecule
How do tRNA synthetases differentiate between similar tRNA molecules?
Identity elements on tRNA molecules
What are identity elements?
Single nonstandard base pairs
What mutation prevents aminoacylation of alanine in tRNA^ala?
G3 or U70
How can aminoacyl tRNA synthetases differentiate very similar amino acids?
Proofreading function
What allows some aminoacyl tRNA synthetases to differentiate between similar amino acids?
Editing site
Aminoacylation/activation site
What is the function of the acylation site of aminoacyl tRNA synthetases?
Rejects amino acids larger than the correct one
What is the function of the editing site of aminoacyl tRNA synthetases?
Hydrolytic cleaves amino acids smaller than the correct one
What is the nomenclature of cognate tRNAs? Using Leu as an example.
tRNA^Leu
What is the nomenclature of cognate tRNA synthetases? Using Leu as an example.
Leucyl-tRNA synthetase
What is the nomenclature of aminoacyl-tRNAs? Using Leu as an example.
Leucyl-tRNA^Leu OR
Leu-tRNA^Leu
Why must some tRNAs recognise more than one codon?
Number of distinct tRNAs is less than number of codons
Describe the Wobble Hypothesis.
First two bases of the codon base pair with the anticodon according to normal rules
Base at 5’ end of anticodon can form non-standard H-bonds with 3’ end of codon
Describe the Wobble prediction of 5’ anticodon A and 3’ codon U.
A converted to I by anticodon deaminase
Describe the Wobble predictions of 5’ anticodon C and 3’ codon G.
No Wobble
Describe the Wobble predictions of 5’ anticodon U and 3’ codon A or G.
U not found as 5’-anticodon base
Describe the Wobble predictions of 5’ anticodon G and 3’ codon C or U.
As predicted
Describe the Wobble predictions of 5’ anticodon I and 3’ codon A or C or U.
As predicted
Give the 4 Wobble base pairs.
I=C
I=U
I=A
G=U
