Translation the basics

1
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

2
Ingredients for translation

• mRNA provides the sequence of codons that
  determines protein sequence
• Ribosomes are complex proteinRNA 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
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

4
The genetic code

• Codons with 3 bases are enough to code for all 20
  amino acids (43 64 but 42 only 16)
• Code has no punctuation so its 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)