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Bacterial Transformation

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1 Bacterial Transformation
Plate 27 Bacterial Transformation

2 Genetic Change Bacterial DNA can undergo changes in several ways:
Transformation Conjugation Transduction

3 Transformation History
1928, a British bacteriologist and medical officer named Frederick Griffith first demonstrated bacterial transformation Streptococcus pneumoniae (AKA “pneumococcus”) can exist in several strains: “S” strain – smooth, encapsulated, deadly “R” strain – rough, unencapsulated, harmless


5 Griffith’s Experiment
Injected mice with the “S” strain of bacteria Result: dead mice Injected mice with the “R” strain of bacteria Result: no sickness or death Injected mice with heat-killed “S” strain of bacteria

6 Griffith’s Experiment
1. 2. 3.

7 Griffith’s Experiment
4. Injected mice with a mixture of harmless “R” strain bacteria and heat-killed “S” strain bacteria Result: dead mice

8 Bacterial Transformation
In order for bacterial transformation to occur, there needs to be: “naked DNA”: DNA not found in a cell (“extracellular” DNA) “competent” bacterial cells: ability to take up extracellular DNA

9 Bacterial Transformation
In Griffith’s experiment, segments of the genetic information from the “S” strain bacteria became “naked” when the cells were heat-ruptured

10 Bacterial Transformation
“Competent” bacteria cells take up DNA segments through their cell membranes Some bacteria cells are naturally “competent” Some bacteria cells can become artificially “competent” through chemicals, heat-shocking, and electro-shocking

11 Bacterial Transformation
Enzymes within the cell cut a segment from the newly acquired DNA The segment gets inserted into the cell’s own DNA In Griffith’s experiment, genes from the “S” strain were transferred to the “R” strain, making it harmful


13 Transformation


15 What do you think? What kinds of applications can bacterial transformation have? In other words, how can people benefit from the use of this technology?

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