Dna & gene therapy
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Dna & gene therapy

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Dna & gene therapy Dna & gene therapy Presentation Transcript

  • PowerPoint to accompanyFoundations in Microbiology Fifth Edition Talaro Chapter 9 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • Microbial Genetics Chapter 9 2
  • Genetics – the study of heredity1. transmission of biological traits from parent to offspring2. expression & variation of those traits3. structure & function of genetic material4. how this material changes 3
  • Levels of genetic study 4
  • Levels of structure & function of the genome• genome – sum total of genetic material of an organism (chromosomes + mitochondria/chloroplasts and/or plasmids) – genome of cells – DNA – genome of viruses – DNA or RNA• chromosome – length of DNA containing genes• gene-fundamental unit of heredity responsible for a given trait – site on the chromosome that provides information for a certain cell function – segment of DNA that contains the necessary code to make a protein or RNA molecule 5
  • Genomes vary in size• smallest virus – 4-5 genes• E. coli – single chromosome containing 4,288 genes; 1 mm; 1,000X longer than cell• Human cell – 46 chromosomes containing 31,000 genes; 6 feet; 180,000X longer than cell 6
  • 7
  • • Nucleic acids are made of nucleotides similar to how proteins are made of amino acids• each nucleotide consists of 3 parts – a 5 carbon sugar (deoxyribose or ribose) – a phosphate group – a nitrogenous base (adenine, thymine, cytosine, guanine, and uracil) 8
  • DNA structure• 2 strands twisted into a helix• sugar -phosphate backbone• nitrogenous bases form steps in ladder – constancy of base pairing – A binds to T with 2 hydrogen bonds – G binds to C with 3 hydrogen bonds• antiparallel strands 3’to 5’ and 5’to 3’• each strand provides a template for the exact copying of a new strand• order of bases constitutes the DNA code 9
  • 10
  • Significance of DNA structure1. Maintenance of code during reproduction. Constancy of base pairing guarantees that the code will be retained.2. Providing variety. Order of bases responsible for unique qualities of each organism. 11
  • DNA replication issemiconservative because each chromosome ends up with onenew strand of DNA and one old strand.
  • Semi-conservative replication of DNA 13
  • DNA replication• Begins at an origin of replication• Helicase unwinds and unzips the DNA double helix• An RNA primer is synthesized• DNA polymerase III adds nucleotides in a 5’ to 3’ direction• Leading strand – synthesized continuously in 5’ to 3’ direction• Lagging strand – synthesized 5’ to 3’ in short segments; overall direction is 3’ to 5’ 14
  • Bacterial replicon 15
  • Flow of genetic information 16
  • • What are the products that genes encode? – RNAs and proteins• How are genes expressed? – transcription and translation 17
  • Gene expression• Transcription – DNA is used to synthesize RNA – RNA polymerase is the enzyme responsible• Translation –making a protein using the information provided by messenger RNA – occurs on ribosomes 18
  • • Genotype - genes encoding all the potential characteristics of an individual• Phenotype -actual expressed genes of an individual (its collection of proteins) 19
  • DNA-protein relationship1. Each triplet of nucleotides (codon) specifies a particular amino acid.2. A protein’s primary structure determines its shape & function.3. Proteins determine phenotype. Living things are what their proteins make them.4. DNA is mainly a blueprint that tells the cell which kinds of proteins to make and how to make them. 20
  • DNA-protein relationship 21
  • 3 types of RNA• messenger RNA (mRNA)• transfer RNA (tRNA)• ribosomal RNA (rRNA) 22
  • 23
  • DNA Transcription RNA polymerase RNA Translation ribosomesPROTEINS 24
  • Transcription1. RNA polymerase binds to promoter region upstream of the gene2. RNA polymerase adds nucleotides complementary to the template strand of a segment of DNA in the 5’ to 3’ direction3. Uracil is placed as adenine’s complement4. At termination, RNA polymerase recognizes signals and releases the transcript• 100-1,200 bases long 25
  • Transcription 26
  • Translation• Ribosomes assemble on the 5’ end of a mRNA transcript• Ribosome scans the mRNA until it reaches the start codon, usually AUG• A tRNA molecule with the complementary anticodon and methionine amino acid enters the P site of the ribosome & binds to the mRNA 27
  • Translation 28
  • 29
  • Interpreting the DNA code 30
  • Translation elongation• A second tRNA with the complementary anticodon fills the A site• A peptide bond is formed• The first tRNA is released and the ribosome slides down to the next codon.• Another tRNA fills the A site & a peptide bond is formed.• This process continues until a stop codon is encountered. 31
  • 32
  • Translation termination• Termination codons – UAA, UAG, and UGA – are codons for which there is no corresponding tRNA.• When this codon is reached, the ribosome falls off and the last tRNA is removed from the polypeptide. 33
  • Polyribosomal complex 34
  • Eucaryotic transcription &translation differs from procaryotic1. Do not occur simultaneously. Transcription occurs in the nucleus and translation occurs in the cytoplasm.2. Eucaryotic start codon is AUG, but it does not use formyl-methionine.3. Eucaryotic mRNA encodes a single protein, unlike bacterial mRNA which encodes many.4. Eucaryotic DNA contains introns – intervening sequences of noncoding DNA- which have to be spliced out of the final mRNA transcript. 35
  • Split gene of eucaryotes 36
  • Multiplication of dsDNA viruses 37
  • Multiplication of +ssRNA 38
  • Regulation of protein synthesis & metabolism
  • Operons• a coordinated set of genes, all of which are regulated as a single unit.• 2 types – inducible – operon is turned ON by substrate: catabolic operons- enzymes needed to metabolize a nutrient are produced when needed – repressible – genes in a series are turned OFF by the product synthesized; anabolic operon – enzymes used to synthesize an amino acid stop being produced when they are not needed 40
  • Lactose operon: inducible operonMade of 3 segments:• Regulator- gene that codes for repressor• Control locus- composed of promoter and operator• Structural locus- made of 3 genes each coding for an enzyme needed to catabolize lactose – β-galactosidase – hydolyzes lactose permease - brings lactose across cell membrane β-galactosidase transacetylase – uncertain function 41
  • Lac operon• Normally off – In the absence of lactose the repressor binds with the operator locus and blocks transcription of downstream structural genes• Lactose turns the operon on – Binding of lactose to the repressor protein changes its shape and causes it to fall off the operator. RNA polymerase can bind to the promoter. Structural genes are transcribed. 42
  • Lactose operon 43
  • Arginine operon: repressible• Normally on and will be turned off when nutrient is no longer needed.• When excess arginine is present, it binds to the repressor and changes it. Then the repressor binds to the operator and blocks arginine synthesis. 44
  • Repressible operon 45
  • Antibiotics that affect gene expression• Rifamycin – binds to RNA polymerase• Actinomycin D - binds to DNA & halts mRNA chain elongation• Erythromycin & spectinomycin – interfere with attachment of mRNA to ribosomes• Chloramphenicol, linomycin & tetracycline-bind to ribosome and block elongation• Streptomycin – inhibits peptide initiation & elongation 46
  • Mutations – changes in the DNA• Point mutation – addition, deletion or substitution of a few bases• Missense mutation – causes change in a single amino acid• Nonsense mutation – changes a normal codon into a stop codon• Silent mutation – alters a base but does not change the amino acid 47
  • Excision repair 48
  • Ames Test 49
  • Types of intermicrobial exchangeconjugation requires the attachment of two related species & formation of a bridge that can transport DNAtransformation transfer of naked DNAtransduction DNA transfer mediated by bacterial virus 50
  • conjugation 51
  • transformation 52
  • Generalized transduction 53
  • Specialized transduction 54
  • Transposons –DNA segments that shiftfrom one part of the genome to another 55