Gene action. Protein function, and when it all goes wrong!. What do proteins do?. Structural genes: produce proteins that become a part of the structure and functioning of the organism
Protein function, and when it all goes wrong!
NORMAL HBB (thalassaemia) GENE SEQUENCE
ABNORMAL HBB (thalassaemia) GENE SEQUENCE
STOPThalassaemia protein product differences
Total: 17 amino acids
Because of ONE change in the DNA sequence, the polypeptide has been shortened by 130 amino acids!!
Base substitutions are USUALLY not too bad. Why?
Because the code can usually continue after the changed sequence. In this case, just one amino acid has changed. BUT if it changes a stop or start codon… then you’re in trouble (as we saw before)
Tyr – gly – trp – ile - asn …
Base additions (insertions) and base deletions
Base additions and deletions can cause lots of trouble! Why?
Tyr- gly- trp- ile- asn …
These are “frame shift mutations” – they change the reading frame, or the triplets. This means that unless a triplet (or multiple of 3) is inserted or deleted, all amino acids after the mutation will be affected.
Let’s figure out this one… <<
Eg. Fragile-X syndrome:
- INDUCED MUTATION – when a causative agent is identified (eg. Cancer-causing UV). Agent is called a MUTAGEN
The effects of Thalidomide were unpredictable and often devastating. Often offspring of a Thalidomide taking mother were born missing limbs, while others were developmentally impaired or had other physical defects. Previous animal tests had not shown these effects, as the drug is not a mutagen to all species.
Recently, Australian families have launched a class action against the inventor of the drug, a German man. The children who were affected are now in their 50s and 60s. The photo is of a patient born with no arms or legs, but is not mentally impaired