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Lecture 7

Lecture 7. Microbial Genetics: Genetic Mutations Gene Transfer. Genetic Mutations. Mutations: Changes in DNA. Why are mutations in DNA important to humans? 2 types of mutations: Spontaneous Mutations :

beverly-leblanc
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Lecture 7

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

  20. Horizontal Gene Transfer • Two types of cells: • Donor: transfers DNA to recipient • Recipient: receives the DNA

  21. Gene Transfer • Three methods of horizontal gene transfer: • Transformation • Transduction • Conjugation

  22. 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

  23. Figure 8.15

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

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

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

  27. 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

  28. R plasmid • Resistance plasmid- confer antibiotic resistance • Two parts: • Resistance genes (R genes) • Resistance transfer factor (RTF)

  29. Figure 8.22

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