Eli5 how a polymerase chain reaction works.
In: Other
First of all – this is how DNA is replicated in a lab.
To understand this, you have to know a little about DNA. If you know about DNA already, feel free to skip this paragraph. DNA is composed to two strands. Each strand is made of 1 of 4 compounds. We call these by letters: A, T, G, and C. Other letters exist, but these are the main ones for human DNA. The important thing is that each compound is paired to another one almost like connecting puzzle pieces – A to T and G to C. If one stand of DNA has an A, the other strand has a T at that same position. This means that one strand (the “sense” strand) tells the body something useful and the other strand (the “antisense” strand) has the opposite compounds. One way to think of this is that the sense strand is similar to a picture, and the antisense strand is like that same picture, but with the colors inverted.
Background over.
The core of PCR is to pull apart DNA and get it to replicate. This is done in a few (simplified) steps.
1. Heat it up – DNA has to be pulled apart to do anything useful, so the bonds holding the letter components together have to be a little weak. Gently heating everything makes the two strands come apart, but doesn’t completely destroy the DNA.
2. Let it cool a little – We now have two different strands to DNA (rather than one double strand). We want to get two double strands (doubling the amount we started with), but to do this, we have to avoid everything falling apart like in step 1. This means we cool everything down just a bit. Before everything clumps together, we jump to step 3.
3. Match the puzzle pieces – I mentioned A goes with T, and G with C. The body has a very complex system to make sure this is done accurately, but we can do it well enough by just letting the DNA sit in an alphabet soup with an enzyme called Taq polymerase. Think of Taq like a toddler grabbing those puzzle pieces and putting them together. At the end of this step, we now have 2 different pieces of double stranded DNA.
3. Repeat – PCR is usually done ~30+ times to get a lot of DNA
Latest Answers