Translation - the basics Synthesis of protein on an mRNA template Sequence of amino-acids in protein (primary structure) determined by sequence of bases in mRNA Uses a triplet code: 3 bases (a codon) code for 1 amino acid Requires a complex assembly of proteins and rRNAs (the ribosome) plus many other factors

Ingredients for translation mRNA provides the sequence of codons that determines protein sequence Ribosomes are complex protein+RNA structures which catalyse protein synthesis tRNA - small RNA molecules that bring together codons on the mRNA and corresponding amino acids Aminoacyl tRNA synthetase enzymes join tRNA and amino acid Protein factors for initiation, elongation, and termination of protein synthesis

3 stages of the translation process Initiation - mRNA, small subunit of ribosome and tRNA charged with 1st amino-acid (methionine) come together, then joined by ribosome large subunit and tRNA with 2nd amino acid Elongation - next aminoacylated tRNA brought into sequence; peptide bond formed to previous amino-acid; move ribosome along mRNA to next position Termination - when a stop-codon is reached, there is no corresponding tRNA; release factors cut protein from last tRNA and ribosome is recycled for translation of another mRNA

The genetic code Codons with 3 bases are enough to code for all 20 amino acids (4 3 = 64 but 4 2 = only 16) Code has no “punctuation” so it’s vital to start “reading” at exactly correct place Code is universal - same in all organisms (with very minor exceptions) Code is degenerate - more than 1 codon for most amino acids (“synonymous” codons) 3rd base in codon can often mutate without changing the amino acid (“silent” mutation)