L10 - Protein Synthesis II

L10 – Protein Synthesis II: Translation and Antibiotics


Slide 3 - The central dogma of molecular biology




Slide 4-5 - Coding properties of nucleic acids

• Three key sets of experiments defined relationship between nuclear DNA and protein
expression
- A messenger exists that transmits information from the nucleus to the cytoplasm
(Brenner, 1960)
- The genetic code is read in triplets (Crick 1961, Nirenberg 1961, Khorana 1960s)
- The amino acid sequence is linearly related to the DNA sequence (Yanofsky, 1967)


Slide 6-9 – The genetic code

• The amino acid sequence of a protein is determined by the sequence of bases on the
DNA strand
• Pairs of bases not enough (only 16 possibilities)
• Triplets of bases more than enough (degenerate code)
• Phenylalanine is the only amino acid incorporated into protein using a cell-free system

, • Genetic code read in triplets
• Code degenerate
- 64 codons for 20 amino acids
- Three special termination codons
- All proteins start with the initiation codon AUG (methionine)


Slide 13-16 – Genetic code: reading frames




Slide 16-18 – Small changes can lead to severe consequences

• Point mutations
- Nonsense mutations: code for a stop, which can truncate the protein