genetic code

Genetic code

Links the sequence of nucleic acids to a protein sequence.

tRNA structural features

73-93 ribonucleotides, L shaped 3D structure, phosphorylated 5’ end, 3’ CCA component, anti codon loop

CCA terminus

Where the amino acid is attached

Anticodon loop

Base pairs to the mRNA codon

Inosine (nucleoside)

Formed by deamination of adenosine

Wobble base pairing

Some tRNAs recognize more than one codon. Yeast alanyl-tRNA anticodon IGC, binds to three codons: GCC, GCU, GCA

tRNA charging

Formation of a peptide bond between free amino acids is thermodynamically unfavourable. Activate intermediates for protein synthesis are amino acid esters called amino acyl tRNAs (charged tRNA)

How are amino acids activated

By adenylation. The amino acyl AMP is transferred to tRNA. Ventilation and transfer is catalyzes by a specific amino acyl tRNA synthatase

tRNA charging 1

Activation by adenylation

Amino acids + ATP → aminoacyl-AMO + PPi

tRNA charging 2

Ester linkage to 3’OH of 3’ adenosine of the tRNA CCA arm

Aminoacyl-AMP + tRNA → aminoacyl-tRNA + AMP

How do amino acyl tRNA synthatase confer specificity

Ex) threonyl tRNA synthatase

Valine can’t interact with the Zn due to its methyl group in place of an OH that Thr has. Ser interacts with Zn due to its OH but is removed at editing site

Why isn’t Thr removed at the editing site in Threonyl tRNA synthatase

Thr can’t fit into the editing site bc it has a methyl group whereas serine has an extra H