chapter 11 - Chapter 11: Genes- Structure, Replication...

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Unformatted text preview: Chapter 11: Genes- Structure, Replication & Mutation Central Dogma • DNA is the key element – Serves as a code for RNA, and ultimately, all proteins – Information within DNA can be transferred from one cell to another = heredity • Replication is necessary to duplicate chromosome(s) • Gene expression = Protein expression = Transcription & translation – Regulation at both levels DNA: The Inherited Genetic Material • First proof that DNA may be the inheritable genetic material came from Griffith’s experiments with pneumococci and mice • Transformation = free (naked) DNA is taken up by a recipient bacterial cell and incorporated into its genome • Griffith’s pneumococci ( Streptococcus pneumoniae ): – Strain S: virulent strain, produced smooth colonies and possessed a capsule – Strain R: nonvirulent strain, produced rough colonies and had no capsule – Hypothesis: Genetic material can be transferred from one strain to another Griffith’s Experiment • Inject a mouse with live R or S strain (controls) – R: the mouse lives; R is re-isolated – S: the mouse dies; S is re-isolated • Inject a mouse with heat-killed S (control) – Expect mouse to live; no S is re-isolated • Inject a mouse with heat-killed S and live R – DNA from dead virulent cells could be transformed into live nonvirluent strain in some cases and expect some mice to die – Re-isolate both R and S (R = newly transformed) Griffith’s Experiment Narrowing the Search • Griffith’s work didn’t show what the genetic material actually was: DNA, RNA, proteins, polysaccharides in the capsule? • Avery, Macleod, and McCarty took Griffith’s experiments further to define what the genetic material responsible for inheritance • They individually extracted and purified biochemical components of the S strain and examined each independently: Polysaccharide, Protein, RNA, DNA Avery, Macleod & McCarthy’s Experiments • Added each individual component in with the nonvirulent R strain then looked at colonial morphology change to indicate capsule formation – Only observed a transformation to smooth (virulent form) when DNA from strain S was present – If DNA from strain S was treated with a DNase, no transformation occurred – Proves DNA is the genetic material Bacterial Genetic Material: Chromosome • Usually 1 dsDNA circular molecule – Exceptions: • Borrelia burgdorferi has a linear chromosome • Rhodobacter sp. have multiple chromosomes • Length of the chromosome is often more than the length of the cell: requires some packaging – Twisted into a supercoiled form – Histone-like proteins are complexed with DNA for structural support Bacterial Genetic Material: Plasmids • Extrachromosomal DNA; much smaller in size than chromosome • Made of circular dsDNA, supercoiled and has histone-like proteins like the chromosome • Contains non-essential genes but ones that would be advantageous under certain conditions • Often include genes for added virulence, antibiotic resistance and genes for using additional carbon and energy sources DNA Structure...
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This note was uploaded on 03/24/2009 for the course MIBO 3500 taught by Professor Dustman during the Fall '09 term at University of Georgia Athens.

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chapter 11 - Chapter 11: Genes- Structure, Replication...

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