Chapter 6 - Transformation

Chapter 6 - Transformation - Transformation

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Transformation Transformation  is the process by which  cells take up DNA  directly from their environment . Terms similar to those used to describe conjugation are used  in discussions of  transformation. DNA derived from a  donor  cell, which may or may not be a bacterium, is taken  up by a  recipient , which then is called a  TRANSFORMANT . Bacterial cells that are in a state where they can take up DNA  are described as being  COMPETENT .
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The Griffith experiments Heat-killed pathogenic  encapsulated bacteria  can convert  nonpathogenic  noncapsulated  bacteria to the  pathogenic capsulated  form. R  indicates  rough- colony  formers. S  indicates  smooth- colony  formers. Roman numerals   indicate  serotype  of  the capsid  polysaccharide,  genetically determined  trait. A B C D Bacterial type        Effect on mouse Bacteria  recovered None Type IIIS None Type IIIS Fig 6.1 Live type IIR Live type IIIS Heat-killed  type IIIS Mixture of live type IIR and heat-killed type IIIS Nonpathogenic Nonpathogenic Pathogenic Pathogenic
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Extract macromolecular components  TRANSFORM LIVE TYPE IIR CELLS IIR IIR IIR IIR IIR +  IIIS The transforming principle is DNA, not polysaccharide Avery, McLeod and McCarthy experiment I Type IIR Type IIIS From P. Russell, iGenetics Type IIIS Heat kill
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1. Cells are given a  fixed amount of  radioactive DNA. 2. The cells are then   treated with Dnase  and collected on a  microfilter (or by  centrifugation). 3. DNA in the cells is  insensitive to DNase.   Degraded DNA will  pass through a filter  (or remain in the  supernatant). The asterisks refer to  radioactively labeled  DNA. Measuring the efficiency DNA uptake by cells Fig 6.4
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 Some bacteria are  naturally competent  and take up naked  DNA at some phase of their life cycle, most commonly in  the late log phase when cell density is high and nutrients  become scarce. EXAMPLES:   Bacillus subtilis  (Gram positive, late log phase) Neisseria gonorrhoeae  (Gram negative, possibly  competent at all stages of growth). 2.  Many bacteria DO NOT take up DNA unless a temporary  state of competence is induced either by a  chemical  treatment , for example, exposure of the cells to  0.1 M  CaCl , or an  electrical shock  ( electroporation ). Natural and induced competence
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Chapter 6 - Transformation - Transformation

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