There are some tools which may only do one thing, but they do it really good. Like how there is a screwdriver available for every screw, and a wrench for every bolt. Now if you want to copy DNA, because every new cell needs it’s own copy of the instruction manual, you need a tool for that. The trick here is that DNA is itself the perfect tool for the job of copying itself. The very structure of DNA, the double helix, is what allows it to copy itself.

We’ve already discussed that DNA is a string of nucleotides, called A, G, C, and T. Here is where the double helix comes in, that’s how DNA actually looks like. The key word here is double. DNA is always found as a pair of two strands, because they naturally pair together. Those loose bases don’t remain loose for very long, A’s and T’s like to pair up, and G’s and C’s like to pair up. So imagine you have two strings, if their sequences are perfectly complimentary, they will naturally stick together. This is called doubled-stranded DNA, and it automatically results in the double helix formation.

But what does that have to do with copying itself? Well, when a cell divides, both of the new cells must have all the DNA, the instructions, which tell it how to behave. To make this new copy, the two strands of DNA split, and from each single strand, the compliment is created, because A’s and T’s always pair and G’s and C’s always pair. In the end you have two complete double helices, each containing one old strand and one new strand.

The very nature of DNA as two fully complimentary strings allows itself to be so easily copied. DNA really is the perfect tool for copying the instructions of life.