Biotechnology
Biotechnology tests the tools of recombinant DNA technology and their applications in medicine, agriculture, and industry. Expect questions on enzymes, vectors, PCR, selection, and the difference between producing a product and proving it works.
Core rules and concepts
- Restriction endonucleases cut DNA at specific palindromic sequences and often leave sticky ends. DNA ligase joins compatible ends. A vector needs an origin of replication, a selectable marker, and a cloning site.
- PCR uses denaturation, primer annealing, and extension. Taq polymerase is thermostable, so it survives the high-temperature denaturation step.
- Gel electrophoresis separates DNA by size; smaller fragments move farther. Bioreactors scale up cultures, and downstream processing purifies the product.
- Applications include human insulin produced from A and B chains, ADA gene therapy, Bt crops, RNA interference against nematodes, and transgenic animals.
Worked example
One DNA molecule is amplified by PCR for five complete cycles. Each cycle doubles the target, so the number of copies is 2⁵ = 32. If 10 molecules start, the total is 10 x 32 = 320 copies. The reasoning uses exponential amplification, not linear addition of five copies.
Traps that cost marks
Restriction enzymes cut DNA; ligase joins it. Taq polymerase is not destroyed at denaturation temperature. A selectable marker identifies transformed cells but does not by itself guarantee gene expression. Ti plasmid is a natural vector from Agrobacterium, not a restriction enzyme.