1. Lecture 7 Microbial Genetics: Genetic Mutations Gene Transfer

2. Genetic Mutations

3. Mutations: Changes in DNA Why are mutations in DNA important to humans? 2 types of mutations: Spontaneous Mutations: –occur in the natural environment without the addition of mutagens (agents that cause mutations) –Occur randomly and spontaneously Induced Mutations: –Mutations that are created by the addition of mutagens

4. Spontaneous Mutations Two types: 1. Base substitutions 2. Frameshift mutations

5. Spontaneous Mutations: Base substitutions Most common type of substitution Mistake during DNA replication, incorrect base incorporated into DNA Three types: 1. Silent mutation: no effect on protein (remember- several codons code for the same amino acid) 2. Missense mutation: codon has changed and different amino acid is incorporated 3. Nonsense mutation: codon has changed to a stop codon

6. Figure 8.15 - Overview

7. Spontaneous Mutation: Base-pair deletion or insertion Insert or delete a nucleotide- very disastrous Shifts codons of DNA when transcribed into RNA (also called frameshift mutation) All nucleotides downstream of mutation will be grouped into improper codons, and wrong amino acids will be added Protein will be non-functional

8. Figure 8.16a

9. Figure 8.16b

10. Figure 8.16c

11. Figure 8.16d

12. Induced Mutation Mutations are induced by either certain chemical mutagens or physical mutagens Sometimes scientists intentionally mutate DNA to study it

13. Chemical Mutagens- Chemical Modification Example: nitrous acid Converts adenine so it no longer pairs with thymine Instead pairs with cytosine

14. Figure 8.17 - Overview (1 of 3)

15. Chemical Mutagens- Nucleoside Analogs Compounds that resemble bases closely

16. Physical Mutagens: Radiation

17. Repair of thymine dimers

18. Gene Transfer

19. Gene Transfer= Vertical Gene Transfer= When genes are passed from an organism to it’s offspring Horizontal Gene Transfer= Occurs between bacteria

21. Horizontal Gene Transfer Two types of cells: 1.Donor: transfers DNA to recipient 2.Recipient: receives the DNA

22. Gene Transfer Three methods of horizontal gene transfer: 1.Transformation 2.Transduction 3.Conjugation

23. Transformation Donor cell wall can rupture, and DNA that is normally tightly packed can break up into pieces and explode through cell wall Naked DNA= These pieces can then pass through cell walls and cytoplasmic membranes of recipient cells and get integrated into their chromosomes

24. Figure 8.15

25. Transduction DNA is transferred from one bacteria to another by virus that infects bacteria (bacteriophage)

27. Conjugation Transfer of DNA by contact of two bacterial cells Can transfer plasmid or chromosome

28. Conjugation Two types of cells: 1.Donor cell- contains fertility plasmid and is designated F + 2.Recipient cell- does not contain fertility plasmid and is designated F - DNA transferred from F + to F -

30. Conjugation In some cells carrying F factors, the F factor integrates into the host chromosome Now called Hfr cell Conjugation between Hfr and F - –Chromosome replicates –Transferred to F - cell –Usually chromosome breaks off before completely transferred –Generally remains F - because does not receive F factor

32. R plasmid Resistance plasmid- confer antibiotic resistance Two parts: 1.Resistance genes (R genes) 2.Resistance transfer factor (RTF)

33. Figure 8.22