Transcript Plasmids
Ecoli Bacteria… remember that 25% of your feces is E coli bacteria…. Plasmids A circular piece of DNA that is not a part of the bacteria’s genome. It is ‘extra-chromosomal.’ Analogy: The Plasmid is the little dog, and the Chromosomal DNA is the big dog. (The cell cannot live without the big dog however…) Typical Prokaryotic Plasmid: Circular, small, and code for things that are useful to the prokaryote, but not necessary. Plasmids give the bacteria extra properties • They can code for toxins – – – Anthrax toxin is caused by a plasmid Botulism is caused by a plasmid. tetanus is caused by a plasmid. Plasmid’s other properties • They can perform nitrogen-fixation (take nitrogen from the air, and use it.) – Klebsiella pneumoniae • Some plasmids make plants grow tumors – This plasmid is known as a Ti (tumour inducing) plasmid Antibiotic resistance Plasmids can code for antibiotics 1. Some bacteria become immune to antibiotics because they have plasmids that make them immune. They can also give their plasmids to other bacteria through transformation. a. b. c. d. e. ampicillin resistance kanamyicin resistance chloramphenicol resistance B-galactosidase resistance Gentamycin resistance Another example antibiotic resistance • Note Gonorrhea – 1989 Resistance went from <0.2% to almost 9% in 10 years! – 1999, resistance is reported to be widespread in the US. – 2000 The Centers for Disease Control found resistance to Cipro – our ‘big gun’ and recommended a whole regimen of treatments: 9 8 7 6 5 4 % Resistant 3 2 1 0 1980 1983 1986 1989 500mg single-dose ciprofloxacin and 400mg ofloxacin as broad-spectrum fluoroquinolones and cephalosporins, respectively, to treat uncomplicated gonorrhea (CDC, 2000). How resistance gets transferred. Plasmids get passed through transformation. Why plasmids are used in genetic engineering • They are easy to put new genes onto: cut the plasmid and the gene you want with the same restriction enzyme…they will ‘match’ and line up… sew them together with ligase enzyme. • Plasmids and bacteria replicate quickly… You get lots of product.. For example: 1. 2. 3. 4. Cut out a gene like insulin with Ecor I Cut open pieces of E. coli plasmid with Ecor I. Mix the new genes and the plasmids together. The new genes will combine with the plasmids because their ends match. 5. Add ligase to sew the parts together 6. Grow a bacterial culture. The bacterial culture will now produce insulin.