1. NOTES – CH 17, part 2 DNA & MUTATIONS

2. MUTATIONS
● permanent changes in DNA that can involve large chromosomal regions or a single nucleotide pair

3. ● 3 Types of Point Mutations:
● POINT MUTATION: mutation limited to about one or two nucleotides in a single gene
● 3 Types of Point Mutations:
Base-pair substitution
Base pair insertion
Base pair deletion

4. 1) Base-pair substitution:
● replacement of 1 nucleotide base pair with another resulting in little or no change in the protein encoded by the mutated gene
-redundancy in the genetic code is why some substitutions have no effect; a base pair change may simply transform one codon into another that codes for the same amino acid.

5. -even if the substitution alters an amino acid, the new amino acid may have similar properties to the one it replaces, or it may be in a part of the protein where the exact amino acid sequence is not essential to its activity.

6. -some base pair substitutions result in readily detectable changes in proteins that may significantly alter protein activity
(i.e. sickle cell anemia; 1 amino acid in hemoglobin is altered)

8. 2) Base pair insertion:
● the insertion of 1 or more nucleotide pairs into a gene

9. 3) Base pair deletion:
● the deletion of 1 or more nucleotide pairs from a gene
-because mRNA is read as a series of triplets during translation, insertion or deletion of nucleotides may alter the “reading frame” of the genetic message

10. -this type of FRAMESHIFT MUTATION will occur whenever the number of nucleotides inserted or deleted is not 3 or a multiple of 3.
-this type of mutation usually results in a nonfunctional protein (unless the mutation is very near the end of the gene)

11. FRAMESHIFT MUTATION:

13. Summary

14. MUTAGENS:
● MUTAGENS = physical or chemical agents that interact with DNA to cause mutations

15. MUTAGENS: ● most mutagens are also carcinogens
● CARCINOGEN = an agent that causes cancer

16. PHYSICAL MUTAGENS:
● x-rays
● UV radiation
● radioactivity

17. CHEMICAL MUTAGENS:
● base analogues (similar to normal DNA bases, but pair incorrectly)
● insert into DNA double helix & interfere with correct DNA replication
● cause chemical changes in the bases that change their pairing properties

18. CHEMICAL MUTAGENS: ● benzene (industrial solvent)
● DDT (& other pesticides)
● nitrogen mustard (in mustard gas, a chemical weapon)

19. CHEMICAL MUTAGENS:
● cigarette smoke! (contains 4000 chemicals, at least 43 of which are carcinogens!!!!)
-nicotine, tar, carbon monoxide, formaldehyde, hydrogen cyanide, ammonia, arsenic, DDT