Microbial Genetics

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  1. Genetics
    The study of genes: What they are, How they carry information, How information is expressed, How genes are replicated and passed on
  2. What is a Gene?
    • Segment of DNA for a functional product
    • Usually 1 gene code for 1 protein
  3. How many genes does E. Coli have?
    4600 genes
  4. How many genes does H. sapiens have?
    • (Humans)
    • 20,000-25,000 genes
  5. What is a chromosome?
    • Structure made of DNA that contains the genes
    • They carry hereditary information
  6. Genome
    All genetic information in a cell
  7. What are the components of the genome?
    Chromosomes and plasmids
  8. Genomics
    The molecular study of genomes
  9. Genotype
    • The genes of an organism
    • An organisms genetic makeup 
    • Represents the potential properties
  10. Phenotype
    • Expression of the genes 
    • Expressed traits of the genotype 
    • Such as its abilities to perform particular chemical reactions and structure
  11. E. coli chromosome
    • DNA contain about 4.6 million base pairs
    • The chromosome is about 1mm long which is 1000 time longer then the cell
  12. The E. coli chromosome so long, how does it fit in the cell?
    • DNA is twisted/Supercoiled 
    • Only take about 10% of cell volume
  13. What is a short tandem repeat (STR)
    • Non coding regions in the Genetic map
    • Repeating sequences of 2- base sequences 
    • Used in DNA fingerprinting
  14. How is the double helix formed?
    2 polynucleotide strands joined by H-bonds forming
  15. How does the bases of the DNA pair?
    Complementary base pairing of purines and Pyrimidines
  16. Purines
    • A and G
    • Adenine and Guanine
  17. Pyrimidines
    • T and C
    • Thymine and Cytosine
  18. On average how many gene bases  are in DNA?
    • about 1000 bases
    • Makes up about 41000 combinations
  19. DNA difference in bacteria and eukaryotes
    • Bacteria DNA is circular 
    • Bacteria in eukaryotes are linear
  20. Where does DNA replication take place in eukaryotes?
    In the nucleus
  21. Where does DNA replication take place in prokaryotes(bacteria)?
  22. Nucleoid
    Irregularly shaped region in prokaryotes that contains most genetic material
  23. What is the first step of DNA synthesis/replication?
    Breaking the H-bonds to seperate the helicase
  24. Replication Fork
    The site at which replication occurs
  25. DNA polymerase
  26. During DNA replication one parental double stranded DNA is converted into what?
    Two identical daughter molecules
  27. DNA Gyrase
    Relaxes the supercoiling of the DNA
  28. Helicase
    Enzyme that unwinds the DNA
  29. What is matched to the exposed bases once the DNA segments are separated?
    • Free nucleotides that are present in the cytoplasm 
    • Where thymine is present on the original strand only adenine can into place on the new strand 
  30. What happens if a free nucleotide are improperly paired?
    It is removed and replaced by replication enzymes
  31. Once the correct nucleotide is in place, what joins it to the new DNA strand?
    DNA Polymerase
  32. DNA ligase
    Makes covalent bonds to join DNA strands
  33. Semiconservative replication
    • DNA replication 
    • Uses 1 original"conserved" strand and 1 new strand.
  34. Why do DNA strands grow in different directions?
    Because DNA ploymerases can only add new nucleotides to the 3' end only.

    • 3' ---> 5'
    • 5' <--- 3'
  35. The energy used for DNA replication comes from where?
    Supplied from nucleotides, which are actually nucleoside triphosphates
  36. Bidirectionally DNA replication
    • Found in some bacteria 
    • 2 replication forks move in different directions away from the origin of rep. 
    • Rep forks usually meet when rep is finished
  37. When the two loops of bidirectional DNA replication meet, how are they separated?
    DNA topoisomerase
  38. Transcription
    Genetic information in DNA is copied, or transcribed, into a complementary base sequence of RNA
  39. Translation
    When the cell uses RNA to synthesize specific proteins
  40. rRNA
    • Ribosomal RNA
    • Forms an integral part of ribosomes
    • The cellular machinery for protein synthesis
  41. mRNA
    • Messenger RNA
    • Carries coded information for making specific proteins from DNA to ribosomes, where proteins are synthesized
  42. Base pairs for RNA
    A, C, G, U
  43. RNA Polymerase
    Synthesizes a strand of RNA (mRNA, tRNA, rRNA) from 1 strand of DNA
  44. Promoter site
    • Starting point of transcription 
    • Proceeds in the 5' --> 3' direction
  45. Terminator Site
    Ending point of transcription
  46. 5 Steps of Transcription
    • 1. RNA polymerase binds to the promoter site, and DNA unwinds at the beginning of the gene
    • 2. RNA is synthesized by complementary base paring of free nucleotides with bases of DNA strand.
    • 3. The site of synthesis moves along the DNA; and transcribed DNA REWINDS
    • 4. Transcription reaches the terminator site
    • 5. RNA and RNA polymerase are released and the DNA helix re-forms
  47. Translation in Eukaryotic cells
    • The process of protein synthesis from mRNA
    • Can only begin once transcription has completed
  48. Codon
    3 base mRNA segments that specifies the amino acid (AA)
  49. In eukaryotic protein synthesis, spliceosomes serve what function?
    Cut out introns from DNA strand leaving only exons for mRNA
  50. Where does transcription and translation occur in eukaryotes? In prokaryotes?
    Eukaryotes carry out transcription in the nucleus and translation in the cytoplasm.

    Prokaryotes perform both processes at the same time in the cytoplasm
  51. Codon Degeneracy
    • Most codon are coded for by >1 codon.
    • Some codons make for the same amino acid such as GAG and GAA.
  52. snRNPs
    • Small nuclear ribonucleoproteins 
    • Remove introns and splice together exons
  53. Start codon
    • AUG 
    • Codes for methionine
    • TAC in DNA
  54. Stop Codons
    • UAG
    • UAA
    • UGA
  55. The site of translation
  56. Sequence of mRNA determines what?
    The sequence of tRNA
  57. Steps of translation
    • -Ribosome binds to the 5' end of mRNA
    • 1st tRNA enters site P, binds to the start codon
    • 2nd tRNA anters site A, where a peptide bonds forms between two AAs
    • Continues down the line until stop codon
  58. Constitutive Genes
    • Their products are constantly produced at a fixed rate.
    • Usually the genes which are turned on all the time code for enzymes that the cell needs in fairly large amounts
    • (Glycolysis)
  59. Adaptive genes
    Genes that are only expressed when needed.
  60. Induction
    The process that turns on the transcription of a gene or genes.
  61. Inducer
    A substance that acts to induce transcription of a gene
  62. Inducible enzymes
    Enzymes that are made in the presence of inducers
  63. Structures of an operon
    • An operon is a segment on the DNA
    • Consists of:
    • Operator- Traffic light. Stop or go for transcription of structural genes 
    • The promoter site- Initiation of transcription
    • The structural genes
  64. A regulatory gene
    • The part of DNA that encodes a repressor protein
    • Switches on/off inducible and repressible operons
  65. Repressible operon
    Structural genes are transcribed until they are turned off or represssed.
  66. Feed back Repression
    • Excess endproduct results in supression of genetic apparatus involed in enzyme production 
    • ONLY alters production, not activity
    • Slow, long-term effects
    • Such as the effects of [tryptophan] and tryptophan production
  67. How does tryptophan operon work?
    • Repressor protein cant bind to operator -> transcription occurs
    • With high [tryptophan], tryptophan binds to repressor protein to form a complex that binds to operator
    • Transcription is blocked
  68. Operon
    Regulatory sequence of DNA that consists of promoter, operator, and structural gene
  69. Feedback inhibition vs Repression
    • Inhibition: Affects enzyme activity, fast acting, short lived effects 
    • Repression: Affects enzyme production, slow acting, longer lived
  70. What is a mutation?
    • A change in the genetic material
    • Mutations may be neutral, beneficial or harmful
  71. Mutagen
    Agent that causes mutations
  72. Spontaneous mutations
    Occur in the absence of a mutagen
  73. Base substitution is also called
    Point mutation
  74. Base substitution and its two subdivisions
    • A single base at one point in the DNA sequence is replaced with a different base
    • a) Missense mutations 
    • b) Nonsense mutations
  75. Missense Mutations
    • When a base substitution takes place in the gene it gives the wrong translation of mRNA.
    • This base substitution results in an A.A. substitution in the synthesized protein

    Ex: Sickle cell disease 
  76. Nonsense Mutation
    • When a base substitution results in a nonsense(stop) codon in the middle of a mRNA molecule. 
    • Only a fragment of a protein is synthesized.
  77. Frameshift mutation
    • One or few nucleotides are inserted or deleted in DNA
    • Causes change in many amino acids
  78. Two types of radiation mutagens
    • Ionizing radiation 
    • Non-ionizing (UV Light) radiation
  79. Examples of Ionizing Radiation
    • X rays
    • Gamma rays
    • Cause formation of ions that react with DNA 
    • May break the sugar phosphate backbone of DNA, which causes  physical breaks in chromosomes
  80. Examples Non-Ionizing(UV Light) radiation
    Cause thymine dimers
  81. How is UV Light mutations fixed?
    • Photolyase enzyme repairs thymine dimers 
    • Nucleotide excision (Dark repair)
  82. Chemical known to cause chemical mutations
    Nitrous Acid
  83. Two types of chemical mutagens
    • Nucleoside Analogs 
    • Nucleotide-altering chemicals
  84. Explain Nucleotide-altering chemicals
    • Nitrous Acid (HNO2)
    • Causes base pair substitution
    • Changed A so that it binds with C vs T
  85. Framshift Chemical Mutagens
    • Benzopyrene 
    • Aflatoxin
  86. Benzopyrene
    • Found in smoke and soot
    • Its an effective framshift mutagen
  87. Aflatoxin
    • Produced by Apergillus flavus
    • Mold that grows on peanuts and grains
  88. Vertical gene transfer
    • Occurs during reproduction between generations of cells
    • (Mother to daughter cells)
  89. Genetic recombination
    The exchange between genes between two DNA molecules to form new combinations of genes on a chromosome
  90. Horizontal gene transfer
    • The transfer of cells between the same generation 
    • The cell that receives the doners DNA is known as the recombinant
  91. Three types of gene transfer
    • Transformation
    • Conjugation
    • Transduction
  92. How Transformation works
    • Naked DNA transferred from dead donor into competent recipient 
    • Donor DNA recombines with recipient 
    • Can confer virulence factors and antibiotic resistant
  93. In transformation the Donor DNA and the recipient DNA are....
    Closely related
  94. Bacterial Conjugation
    • Mating 
    • Involves a plasmid (a circular piece of DNA the replicates independently from cells chromosomes) AKA F factor 
    • Requires direct cell to cell contact between
  95. What does the plasmid in conjugation do?
    • In gram (-) it carries the code for the synthesis of sex pilli
    • In gram (+) cells produce a sticky surface that cause cells to come into direct contact
  96. F Factor
    • The fertility factor
    • Cells with are F+; cell without are F-
  97. Hfr
    High frequency recombination
  98. Transduction
    • Virus(Bacteriophage) acts as a genetic vector, passing DNA from donor to recipient
    • Two types: Generalized and specialized
  99. Generalized transduction
    • Random transfer of any genes
    • Donor infected with bacteriophage 
    • Donor DNA fragments surrounded by capsids
    • Donor lyses, viral vector released and infects recipient 
    • Donor DNA combines with recipients DNA
    • Abortive if it fails to recombine 
    • Can confer virulence factors and antibiotic resistance
  100. Specialized transduction
    • Only certain genes are transferred 
    • Donor has viral DNA integrated into own DNA(Prophage)
    • Viral DNA pops out of donor DNA with same DOnor DNA attached
    • (HIV cells becomes apart of DNA)
  101. What are plasmids?
    • Additional genetic material 
    • Found in Prokaryotes and Eukaryotes 
    • Circular DNA
    • Self-replicating 
    • Non-esential
    • Many types (R-Factor)
  102. R Factor
    Resistance Factor
  103. What are transposons
    • Small DNA segments that are capable of moving 
    • AKA Jumping genes
    • Can move on same chromosome or to different chromosomes or plasmids
  104. DNA segments that are able to jump between unrelated species (via plasmids or viruses)
Card Set:
Microbial Genetics
2014-05-08 07:55:46
Microbial Genetics
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