1. Microbial Genetics

2. What is the genetic material?  DNA Nucleotide base pairs  A-T, C-G Chromosomes  Bacteria: circular  Chromatin  Genetics Genes Genome Genetic code

3. What is the purpose of DNA?  Recipe for making _____________  Genotype vs phenotype

4. What’s special about bacterial DNA?  Circular  Attached to PM at various pts

5. How is DNA copied for replication?  Recall DNA structure  Replication Overview DNA helicase unwinds double helix DNA polymerase III copies at replication fork  Replication is 5’ to 3’ Ligase “glues” nucleotides Animation

6. What is semiconservative replication?

7. What are the specifics of DNA replication?  DNA strands are antiparallel  Bidirectional replication animation Bidirectional replication animation  Rolling circle animation Rolling circle animation  Replication always starts at new 5’ end Leading strand Lagging strand  Okazaki fragments (started with an RNA primer) Okazaki fragments  Error rate: 1 in 10 10

8. Protein Synthesis

9. How does DNA direct protein synthesis?  Via RNA Three types of RNA  tRNA, rRNA, mRNA  Overview: mRNA is copy of DNA gene  Created by transcription Protein made during translation  Ribosome “reads” triplet genetic code  tRNA delivers appropriate amino acid

10. What happens in transcription?  mRNA created Often translation occurs while transcription happens Base pairing  No T in RNA, instead U Begins with RNA polymerase attaching to promoter region of coding strand Stops when reaches terminator region transcription process transcription process

11. What happens in translation?  Ribosome attaches to mRNA Reads codons  Code is redundant (degenerate)  20 aas, but 61 codons  3 stop codons (nonsense codes)  Start codon (______) in bacteria codes for formylmethione tRNA brings in appropriate aa  Matches to tRNA anticodon

12. How does the ribosome “read” the mRNA?  Ribosome finds start codon 30S attaches, then 50S First tRNA to P site  Second to A site First tRNA transfers aa to aa on A site tRNA  Ribosome shifts Moves 5’  3’ New tRNA into now open A site Process repeats translation

13. How many ribosomes can work at once?

14. Is it the same process in eukaryotes?  Pretty much  Exception: DNA is inside nucleus Post- transcriptional modifications  5’ cap  3’ poly-A tail  Introns removed

15. Control of Genes, Mutations and DNA Recombination

16. What controls gene expression?  Majority of genes are constitutive Protein produced at constant rate  Repression Inhibit gene expression Repressors: proteins that repress  Induction Turning on transcription Inducer: substance that induces  Lac operon model demonstrates these two processes

17. What is induction?  Induction Turning on transcription Inducer: substance that induces  Lac operon model demonstrates these two processes

18. What is repression?  Repression Inhibit gene expression Repressors: proteins that repress

19. What is the lac operon model?  Study of E. coli Inducible system when lactose is present  Three genes for lactose consumption next to each other on chromosome These are structural genes  DNA nearby is control region Includes promoter and operator Together these are the operon Lac operon = 3 lac genes + operon region General regulation animation General regulation animation Animation

20. Regulation of Gene Expression Figure 8.13

21. What happens if the DNA code is wrong?  Called a mutation Causes change to mRNA sequence which can affect translation and thus ___________  Spontaneous  Induced  Excision repair

22.  Nonsense mutation Mutation  Results in a nonsense codon Figure 8.16a, c

23. Mutation  Frameshift mutation  Insertion or deletion of one or more nucleotide pairs Figure 8.16a, d

24. What types of mutation are there?  Original: THE BIG FLY HAD ONE RED EYE.  Point mutation: THE BIT FLY HAD ONE RED EYE.  Frame shift mutation:  Addition:  THE BIT GFL YHA DON ERE DEY E.  Deletion of G in BIG:  THE BIF LYH ADO NER EDE YE.  Which is more dangerous? mutations movie  Spontaneous mutations  Mutagens Can affect pathogeneticity

25. What can be a mutagen?  Chemicals Nitrous acid Nucleoside analog  Similar to normal nitrogenous base  Causes mismatching of base pairs AZT (azidothymidine) does this  Radiation Formation of thymine dimers  Light-repair enzymes (photolyases)  animation animation

26. Mutagens vs Carcinogens: what the difference?  Mutagens  Carcinogens  Ames test Identifies possible carcinogens by identifying mutagens Looks to see how many mutate Salmonella cells revert to a nonmutant form

27. How can bacteria pass DNA?  Genetic recombination Exchange of genes between chromosomes Gives new combinations  Vertical gene transfer Parent to offspring  Horizontal transfer 3 types…

28. What is conjugation?  Horizontal gene transfer (1% of population) Donor bacterial cell gives DNA to recipient cell  Recipient now has recombinant DNA  Conjugation  Process in E. coli Donor is F+, recipient F- F= fertility factor Hfr cell (high frequency of recombination  When F factors integrate into chromosome  Conjugation-plasmid Conjugation-plasmid  Conjugation-chromosome Conjugation-chromosome

29. What is transduction?  Virus transfer DNA  general vs. specialized  animation animation

30. What is transformation?  Gene transferred to recipient bacterium  Griffith (1928) Studied Streptococcus pneumoniae  Two strains: one virulent, one not  Transformation animation Transformation How could this happen???!!

31. What are transposons?  Jumping genes  Can be transferred to other cells