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Microbial Genetics

Microbial Genetics. What is genetics?. Study of inheritance and traits expressed in the genetic material of the organism. GENOTYPE: genetic “ make-up ” of the organism PHENOTYPE: expression of the genotype - the organism and its traits. Genome. Entire genetic compliment of the organism.

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Microbial Genetics

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  1. Microbial Genetics

  2. What is genetics? • Study of inheritance and traits expressed in the genetic material of the organism. • GENOTYPE: genetic “make-up” of the organism • PHENOTYPE: expression of the genotype - the organism and its traits.

  3. Genome • Entire genetic compliment of the organism. • DNA - all prokaryotes and eukaryotes • DNA or RNA - viruses

  4. Structure of DNA • Until 1953 the exact structure of DNA was unknown. • James Watson and Francis Crick discovered the structure of DNA. • In 1962, Crick, Watson, and another researcher named Wilkins were awarded the Nobel prize of this work.

  5. Watson and Crick with the model of DNA

  6. The Watson-Crick model • The model proposes the following: • DNA molecule is a double helix • The “backbone” of the helix is composed of the sugar, deoxyribose, alternating with a phosphate group • Four nitrogenous bases form the interior “ladder” of the molecule and carry the genetic code for life

  7. Nitrogen Bases in DNA • Adenine, thymine, guanine, cytosine • The bases ALWAYS pairs as follows: • Adenine-Thymine • Guanine-Cytosine • Base pairs are held together by hydrogen bonds

  8. Base Pairing

  9. Key Terminology • 1. REPLICATION – new copy of DNA being made • 2. TRANSCRIPTION – gene being copied from DNA sequence into messenger RNA • 3. TRANSLATION – mRNA read and protein produced

  10. Central Dogma of Molecular Biology

  11. DNA Replication(the secret is in the base pairing) • 3’ A-T-G-G-C-T-G-T-C-G-G-C-T 5’ • 5’ T-A-C-C-G-A-C-A-G-C-C-G-A 3’ • The strands run ANTI-PARALLEL • DNA Replication is said to be SEMI-CONSERVATIVE • http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/bio22.swf::Meselson and Stahl Experiment

  12. Semi-conservative replication

  13. DNA Replication

  14. Structure of deoxyribose • The carbons are numbered 1’ to 5’ • The phosphate is linked to the sugar between the 3’ and 5’ carbons • Sugar – phosphate backbone

  15. 5’ and 3’ ends of DNA • The 5’ end has the free phosphate (P) • The 3’ end is the free OH end • The strands are anti-parallel

  16. Direction of replication • DNA replication proceeds 5’→ 3’ • A free 3’ end is needed to add another nucleotide

  17. DNA Replication • 1. The molecule “unzips” to expose free ends. One is the 3’ end the other is the 5’ end • 2. DNA synthesis can now begin • 3. Synthesis on the free 3’ end is CONTINUOUS, this is called the LEADING STRAND • 4. Synthesis on the free 5’ end is DISCONTINUOUS, this is the LAGGING STRAND • 5. The enzyme that is responsible for DNA synthesis on BOTH strands is DNA polymerase BUT this enzyme requires a free 3’ end at which it can add new bases!

  18. DNA Replication(continued) • 6. Synthesis of the lagging strand is in short segments of DNA, about 1000 bases • 7. These short segments are called OKAZAKI FRAGMENTS • 8. The enzyme DNA ligase seals the gaps between these fragments to produce a gaps free discontinuous strand

  19. Directions of replication

  20. RNA compared to DNA

  21. Types of RNA • 1. Messenger RNA (mRNA) • 2. Ribosomal RNA (rRNA) • 3. Transfer RNA (tRNA)

  22. Transcription • 1. This is the process of making a copy of a gene (sequence of DNA that codes for a protein or functional product) • 2. The enzyme responsible for this process is RNA POLYMERASE • 3. Copies the gene is a 5’→ 3’ direction • 4. Gene transcription begins at a site called the PROMOTER and ends at another site called the TERMINATOR

  23. Transcription(making mRNA)

  24. Example of transcription and translation • 3’ TACAGAGTACGAACT 5’ (antisense) this is copied • 5’ ATGTCTCATGCTTGA 3’ (sense)    • 5’ AUG|UCU|CAU|GCU|UGA 3’ mRNA (gene copy) • 3 bases = codon = amino acid • Met-ser-his-ala-stop Protein • 3’strand of DNA is the TEMPLATE or ANTISENSE strand THE STRAND THAT IS COPIED! • 5’ strand of DNA is the INFORMATIONAL or SENSE strand

  25. Transcription (s

  26. Another example of transcription • 3’ GGGGGGGGGGGGGGG 5’ anti-sense • 5’ CCCCCCCCCCCCCCC 3’ sense Transcription (anti-sense) 5’ CCCCCCCCCCCCCCC 3’ Translation Pro-pro-pro-pro-pro-pro- Remember-copy the 3’ strand and by the rules of base paring you get the sense strand sequence!

  27. Genetic code

  28. Protein Synthesis(Translation)

  29. Translation

  30. Translation

  31. Translation

  32. Translation

  33. Transfer RNA

  34. Exons and Introns • 1. These are terms unique to eukaryotic cells • 2. EXONS are information regions in DNA that must be expressed • 3. INTRONS are non-coding regions in DNA that are not expressed

  35. RNA processing in eukaryotic cells

  36. Control of Gene Expression • 1. Control is at the level of TRANSCRIPTION • 2. Genes that are NOT needed are NOT expressed, i.e., the gene is not transcribed • 3. Many genes are always expressed because the cell always needs the gene product • 4. Such genes are CONSTITUTIVE

  37. Genetic Control • 1. REPRESSION – inhibition of gene expression • 2. INDUCTION – switching on gene expression

  38. Model of Inducible Gene System • Lactose operon • OPERON is defined as a set of operator and promoter sites and the genes that they control • Described in E. coli by Francois Jacob and Jacques Monod • Genetic ON/OFF switch

  39. Operon

  40. Off and On of the lac operon

  41. Tryptophan operon(repressible operon)

  42. Mutations • Change in the base sequence of DNA • May or may not have an effect on the organism • The potential magnitude of the change depends on the gene affected

  43. TACTTCAAACCGATT AUGAAGUUUGGCUAA Met-lys-phe-gly-stop TACTTCAAATCGATT AUGAAGUUUAGCUAA Met-lys-phe-ser-stop MISSENSE MUTATION BASE SUBSTITUTION

  44. TACTTCAAACCGATT AUGAAGUUUGGCUAA Met-lys-phe-gly-stop TACATCAAACCGATT AUGUAGUUUGGCUAA Met-STOP NONSENSE MUTATION BASE SUBSTITUTION

  45. TACTTCAAACCGATT AUGAAGUUUGGCUAA Met-lys-phe-gly-stop TACTTCAACCGATT AUGAAGUUGGCUAA…. Met-lys-leu-ala…. FRAMESHIFT MUTATION BASE DELETION

  46. Bacterial SEX!!! • 1. Transformation • 2. Conjugation • 3. Transduction

  47. Transformation(Griffith 1928)

  48. Transformation

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