Biotechnology: Process and Application
Easy Overview
Imagine being able to cut, paste, and copy genes like you edit a Word document. That's biotechnology. This chapter shows you the tools and tricks scientists use to hack DNA — restriction enzymes (molecular scissors), vectors (gene taxis), and PCR (a photocopier for DNA).
Restriction enzymes — molecular scissors
Bacteria have these enzymes to chop up invading virus DNA. Scientists stole the idea. Each restriction enzyme cuts DNA at a specific sequence (recognition site). Some cut straight through (blunt ends), some leave sticky overhangs. Sticky ends are great because they can stick to complementary cuts from other DNA.
Vectors — the delivery guys
You can't just inject a gene into a cell and hope for the best. You need a vehicle — a vector. Plasmids (small circular DNA in bacteria) are the most common. You cut the plasmid and the gene you want with the same enzyme, mix them, and DNA ligase glues them together. Now you've got recombinant DNA.
PCR — making millions of copies
PCR is a DNA photocopier. Take a tiny bit of DNA, add primers (short starting sequences), nucleotides, and a heat-tolerant DNA polymerase (Taq polymerase). Then cycle through heat (denature), cool (anneal primers), and warm (extend). Every cycle doubles the DNA. In an hour you can make a billion copies from one strand.
Gel electrophoresis — separating DNA by size
After you cut DNA with restriction enzymes, how do you see the pieces? Run them through a gel. DNA is negative, so it moves toward the positive end. Small pieces run fast, big pieces lag behind. You get a ladder of bands. It's like a race where the smallest runners finish first.
DNA fingerprinting — who left this DNA?
Everyone's DNA is unique (except identical twins). DNA fingerprinting uses restriction enzymes to cut DNA at specific spots, then compares the band patterns. Used in crime scenes, paternity tests, and identifying disaster victims. It's like a barcode for your genetic identity.
Gene therapy — fixing broken genes
Some diseases happen because a gene is defective. Gene therapy tries to fix it by inserting a working copy. The healthy gene is delivered via a vector (usually a modified virus) into the patient's cells. It sounds sci-fi, and it's still experimental, but it's already been used for SCID (bubble boy disease).
Key Points
- •Restriction enzymes cut DNA at specific palindromic sequences
- •Sticky ends help in joining DNA from different sources
- •Plasmids are common vectors — cut, insert gene, ligate, transform into host
- •PCR: denaturation (94°C), annealing (50-65°C), extension (72°C) — 25-35 cycles
- •Taq polymerase is heat-stable, from Thermus aquaticus bacteria
- •Gel electrophoresis separates DNA fragments by size; smaller = faster
- •DNA fingerprinting uses VNTRs (variable number tandem repeats) for identification
- •Gene therapy delivers functional genes to correct genetic disorders
Practice Questions
- Describe the steps involved in making recombinant DNA using a plasmid vector.
- Explain the three steps of PCR and why Taq polymerase is essential.
- How does gel electrophoresis separate DNA fragments? Why does DNA move toward the positive electrode?
- What are restriction enzymes? How do sticky ends and blunt ends differ?
- List two applications of DNA fingerprinting and explain the principle behind it.