transfer RNAs

what are tRNA molecules

read the genetic code in mRNA and deliver corresponding amino acid to the ribosome to be added to the growing polypeptide chain

what is a tRNA with an amino acid attached called?

amino acyl tRNA

what enzyme links an amino acid added to a tRNA?

aminoacyl-tRNA synthetase

how many synthetases are there?

20 different synthetases, one for each amino acid

how do aminno-acyl tRNA synthetases work?

• link amino acid to free 2’/3’ hydroxyl of the adenosine at the 3’ terminus of the tRNA molecule

• reaction requires ATP

• forms high energy bond which later drives peptide bond formation between amino acids

how many different tRNAs are there in plant and animal cells

50-100 tRNAs

many amino acids have more than one tRNA, tRNAs can pair with more than one codon

amino acids < tRNAs < codons

how are tRNA molecules formed?

tRNA gene template is transcribed and translated

primary structure folds into precise 3-D structure

what is the structure of tRNA

clover leaf structure with anticodon at one end and free 5’ and 3’ at the other end

what is the free 5’ and 3’ end called?

the acceptor stem (accepts a amino acid)

3’ end sequence always ends CCA

what is the wobble effect/non-standard base pairing?

• ability of tRNAs to recognise more than one codon due to non-standard base pairing in the ‘wobble position’

• wobble position = 3rd base in mRNA codon/1st base in tRNA anitcodon

• base 1 and 2 of mRNA always form standard base pair with base 2 and 3 of anticodon

what base can tRNAs contain that neither DNA nor RNA contains

inosine (I) - can pair with C, A, U

is a deaminated product of adenine

what are the different non standard base pairs that can be formed?