Origins of biotechnology was to solve/cure diseases. Rna polymerase moves only in the 5 prime to 3 prime direction. Reverse transcriptase moves the opposite way from 3 prime to 5 prime (mrna back to dna) This helped engineering to solve diseases cdna: single stranded dna going in the opposite direction (3"-5") made from reverse transcriptase. Plasmid: small, circular dna in bacteria that replicate independently of the chromosome. Can be served as a vector to transfer recombinant genes to new host. Restriction endonucleases: enzyme that has short template of nucleic acids built in that can go find dna with complementary base sequence. It moves down the dna to find its palindrome, bind, cut dna around complementary sequence giving the bacteria two open sticky ends. This base sequence they cut is called a recognition site. Take the restriction enzyme to cleave our own dna to make a short complementary base sequence to enter into the open ends of the plasmid.