Biotechnology and Its Applications
Scope
The exam tests recombinant DNA tools, cloning vectors, PCR, gene cloning, transgenic organisms, biopharmaceuticals, gene therapy, RNA interference and biosafety.
Core rules
- Restriction endonucleases cut at palindromic recognition sites; sticky ends allow complementary base pairing.
- DNA ligase seals nicks between sugar and phosphate backbones.
- A vector needs an origin of replication, selectable marker and recognition sites; plasmids and bacteriophages are common.
- PCR uses denaturation, primer annealing and extension; Taq polymerase survives high temperatures.
- Bt cotton carries cry genes; the toxin is inactive in the bacterium and becomes active in the alkaline insect midgut.
- Gene therapy delivers a functional gene; ex vivo cells are modified outside the body and returned.
Worked example
One double-stranded DNA molecule is amplified by PCR for 5 complete cycles. How many copies are present? Reasoning: each cycle doubles the number of target molecules, so after n cycles there are 2^n copies. For n = 5, 2^5 = 32. This assumes 100% efficiency; real PCR is less efficient and plateau effects occur.
Traps
- Restriction enzymes do not cut randomly; they recognise specific sequences.
- Taq polymerase lacks proofreading, so PCR products can carry errors.
- Bt toxin does not kill the bacterium itself because it is produced as an inactive protoxin.
- Insulin produced by rDNA technology is human insulin, not extracted pig insulin.