Download 10. Genetic engineering and bacteria

23 May 2017
Today’s Title: CW: Genetic engineering and bacteria
Learning Question: how can bacteria take up genetic
information from other organisms?
Aims from specification
(l) describe the advantage to
microorganisms of the capacity to take up
plasmid DNA from the environment
Why do we want to genetically engineer
organisms?
• Improving a feature of the recipient organism
– Inserting a gene into a crop plant to give herbicide resistance – increase crop yield while
controlling weeds
– Inserting growth-controlling gene into cattle e.g. myostatin to promote muscle growth
• Engineering organism that can synthesise useful products
– Inserting the gene for a human hormone e.g. insulin or somatotrophin into a bacteria
and growing the bacteria produces large quantities of the hormone for human use
– Inserting gene for pharmaceutical chemical into female sheep so that it is produced in
milk and easily collected
– Inserting gene for beta-carotene production into rice so that the molecule is present in
the edible part of the rice plant. Beta-carotene can be converted into vitamin A in people
who eat it.
Bacterial cells and plasmids are often
used in genetic engineering
• Identified gene can be cut using restriction enzymes and then placed in a
vector.
• Bacterial plasmids are often used as vectors – plasmids are small, circular
pieces of DNA found in many bacteria types.
• Plasmids are separate from main chromosomes and often carry genes for
antibiotic resistance.
• Plasmids cut with same restriction enzyme used to cut out gene,
complementary sticky ends form.
• In the presence of the enzyme ligase, they will reseal to reform the
original plasmid
Transformed and transgenic bacteria
• Large quantities of plasmids and bacterial cells are mixed with calcium
salts and “heat shocked” to stimulate uptake of plasmid by bacterial host.
• Heat shocking – culture temperature is lowered to freezing then quickly
increased to 40oC to increase their ate at which plasmids are taken up
• Inefficient process – about 0.25% of plasmids are taken up
• Bacteria that do take up altered plasmids are described as transformed
• Transformation results in bacteria containing new DNA – they are now
transgenic bacteria
Bacterial conjugation and the advantages
of taking up new DNA
Bacterial conjugation and the advantages
of taking up new DNA
• Swapping copies of plasmid DNA between bacteria.
• Can occur between different species of bacteria
• Significant as plasmids carry genes for antibiotic
resistance
– Serious health risks to humans (MRSA)
Bacterial transformation and
pneumonia in mice
Questions
1. Suggest how the DNA content from the Sstrain differs from that in the R-strain
Pneumococcus
2. Apart from DNA take-up as described above,
what other genetic process could give rise to
genetic variation in bacterial cells?
Answers
1. The S-strain bacteria and the R-strain
bacteria both contain the bacterial
chromosome; however, the S-strain bacteria
also contain a plasmid. The gene for
production of pneumococcal toxin is present
on the plasmid
2. Mutation