Microbiology Chapter 8 PDF

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Microbiology Chapter 8: Microbial Genetics Terms to Remember: 

Genes: determine functioning at cellular level; area of chromosome that translates into specific peptic acids that turn into a trait/characteristic

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Chromosome: strands of DNA – phosphates and sugars form backbone; carries genes; crux of gene structure

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Genome: complete set of genes or genetic material present in a cell

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DNA: carrier of genetic information

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mRNA: messenger RNA; created during transcription; carries portion of DNA code to other parts of the cell for processing

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Ribsomes: found in cytoplasm; consist of RNA and associated proteins; bind mRNA + transfer RNA to synthesize polypeptides and proteins

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tRNA: transfer RNA; carry amino acids to ribosomes to be synthesized into proteins (amino acids)

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Purines (adenine, guanine)  A-T, A-U (RNA), G-C

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Pyrimidines (thymine, cytosine, uracil—in place of thymine in RNA)

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Genotype: the genes you have

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Phenotype: that traits that you have due to the genes (genotype) you have o EX: red stained bacteria; phenotype is redness; sequence of bases in bacteria is the genotype

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Codon: sequence of 3 nucleotides that form a unit of genetic code in DNA or RNA

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Anticodon: sequence of 3 nucleotides forming a unit of genetic code in a tRNA molecule, corresponding to a complementary codon in mRNA

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Haploid: one set of chromosomes; any change in genetic structure will be displayed and expressed quickly; easy to study; disadvantage = changes can affect cells tremendously (could be an advantage, or could kill the cell)

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Diploid: 2 sets of chromosomes; can be advantageous or disadvantageous

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Mutation: permanent change in genetic code/structure

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Vertical gene transfer: from parent to offspring

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Horizontal gene transfer: from cell to cell

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Spontaneous mutation: naturally arising mutation, not because of exposure to a mutagen

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Silent mutation: changes that occur but rarely impact functioning of the cell or cause any visible change

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Point mutation: a mutation affecting only one or very few nucleotides in a gene sequence

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Missense: point mutation in which a single nucleotide change results in a codon that codes for a different amino acid

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Nonsense mutation: mutation in which a sense codon that corresponds to one of the twenty amino acids specified by the genetic code is changed to a chainterminating codon (?)

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Frameshift mutation: caused by insertion or deletions of nucleotides in DNA sequence that changes the entire sequence

Transcription + Translation (Protein Synthesis) 

Transcription: basis of producing functional products, generation/production of mRNA; process by which information in a strand of DNA is copied into a new molecule of mRNA

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Translation: cell begins to read the sequence of bases on the mRNA; mRNA is decoded to produce specific sequence of amino acids in a polypeptide chain

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Transcription generates 3 kinds of RNA: mRNA, tRNA, rRNA o tRNA carries amino acids during protein synthesis o rRNA = ribosomal RNA: molecular component of ribosomes; makes polypeptides that go on to make amino acids that then create proteins

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Protein synthesis o Prokaryotes: no nucleus (*basis of difference b/w pro + eukaryotes*), no processing (splicing), transcription and translation occur quickly and simultaneously, takes place in the cytoplasm

o Eukaryotes: nucleus, transcription takes place in the nucleus, processing/splicing occurs; exons = coding, introns = non-coding; splicing removes the non-coding introns Mutations 

Caused by: change on cellular level or gene structure that causes a genetic mutation o Chemical 

Nitrous acid acts by chemically modifying the bases of DNA; wrong base pairings; faulty pairings can impact the body on a cellular level

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Nucleoside analog: base substitution, some inhibit DNA replication; used in therapeutic drugs to treat HIV; prevents spread of disease; disadvantage = effects human cells

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Benzopyrene: found in charbroiled food and cigarette smoke; carcinogenic; inhaling this can cause cancer + a mutation in the lungs resulting in abnormal or cancerous cells

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Aflatoxin: poisonous carcinogens produced by certain molds; found in soil; peanuts

o Radiation 

X-rays

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UV light + gamma rays – antimicrobial agent, causes errors in DNA

and replication 

UV light – must be careful how much you expose your skin to; can cause mutations that lead to skin cancer 

Exposure to UV causes adjacent (right next to each other) thymines to become cross-linked, forming a thymine dimer and disrupting their normal base pairing

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Enzymes will see this faulty pairing and insert a new, correct pair

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Endonuclease cuts the DNA, an exonuclease removes damaged DNA

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DNA polymerase fills the gap by synthesizing new DNA, using the intact strand as a template

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DNA ligase seals the remaining gap by joining the old + new DNA

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If you subject skin to constant UV exposure, the cells eventually give up

Repair mechanisms 

DNA polymerase: enzyme that forms new copies of DNA in the form of nucleic acid molecules

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Mismatch repair: system for recognizing and repairing mutations of bases during DNA replication and recombination

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Light repair: repair that happens in the presence of light

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Dark repair: repair that happens in the presence of darkness

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Excision repair: repairs damaged DNA throughout the cell cycle

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SOS repair: if a cell is exposed to mutagens and very damaged, will go into an SOS repair mechanism; replicate despite mutations

Ames Test 

Tests chemical (mutagens) on mutant bacteria that lack repair mechanisms (Salmonella), often carcinogenic; a test to determine the mutagenic activity of chemicals by observing whether they cause mutations in sample bacteria

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Bacteria that lack repair mechanisms cannot repair itself, so it will express the mutation immediately

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99% of the time are carcinogen  cause cancer

Gene transfer 

How bacteria pass on new genes/mutation...