Transcript Plate 27 - Bacterial Transformation

Plate 27
Bacterial Transformation
Genetic Change
• Bacterial DNA can undergo changes in
several ways:
– Transformation
– Conjugation
– Transduction
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
Griffith’s Experiment
1. Injected mice with the “S” strain of
bacteria
•
Result: dead mice
2. Injected mice with the “R” strain of
bacteria
•
Result: no sickness or death
3. Injected mice with heat-killed “S” strain of
bacteria
•
Result: no sickness or death
Griffith’s Experiment
1.
2.
3.
Griffith’s Experiment
4. Injected mice with a mixture
of harmless “R” strain
bacteria and heat-killed “S”
strain bacteria
•
Result: dead mice
4.
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
Bacterial Transformation
• In Griffith’s experiment, segments of the
genetic information from the “S” strain
bacteria became “naked” when the cells
were heat-ruptured
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, heatshocking, and electro-shocking
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
Transformation
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?