On the right is the Recombinant DNA tab. At the top is the source DNA carrying the wanted gene (e.g. the insulin gene); below it a circular bacterial plasmid. A restriction enzyme recognises one specific sequence and cuts both of them at the same site, leaving short single-stranded sticky ends. ▶ Play to watch the scissors snip the gene free and open the plasmid.
Because the same enzyme cut both, the gene and the opened plasmid have matching sticky ends. ⏭ Step on and watch the gene drift into the gap — its overhang base-pairs with the plasmid's. Then the enzyme DNA ligase acts as glue, sealing the sugar–phosphate backbones into one continuous ring: a recombinant plasmid.
↻ Reset, then ▶ Play to the end. The recombinant plasmid is taken up by a host bacterium — it is now transformed. Watch the bacterium divide again and again: each daughter cell carries a copy of the plasmid and the gene. This is gene cloning, and every cell now reads the gene and makes the human protein, ready to harvest.
Switch to the PCR tab. PCR makes millions of copies of a DNA piece. Watch the thermometer: first it climbs to about 95 °C — denaturation. The intense heat breaks the hydrogen bonds and unzips the double helix into two single strands. ▶ Play to start the cycle and follow the temperature.
The temperature now falls to about 55 °C — annealing — and short primers bind to each separated strand. Then it rises to about 72 °C — extension — where heat-stable Taq polymerase builds a new complementary strand. The count tile shows the result: each full cycle doubles the DNA — 1 → 2 → 4 → 8. ⏭ Step through the cycles and watch the copies multiply.
Open the Applications tab. ▶ Play and the panel builds up the great uses of this technology one card at a time: insulin & human proteins, GM crops (pest-resistant Bt cotton, vitamin-A Golden Rice), gene therapy to fix faulty genes, and DNA fingerprinting for forensics. The same toolkit — cut, paste, copy — powers them all. Revisit the full detail in the Lecture.