These are the chemical structures of the nucleotides that are the building blocks of the most important molecule on earth: DNA/RNA. But, they look more fun as Tetris bricks.
Cytosine and thymine are molecules in the ‘pyrimidine’ class, and adenine and guanine are ‘purines’. DNA is made up of A, T, C, and G’s with the A’s pairing with the T’s and the C’s pairing with the G’s. RNA is made up of A, C, G, and U’s (uracil is used instead of thymine), it is structured exactly like DNA (the only difference is A’s with U’s), but this small difference gives the two molecules vastly different structures and functions.
DNA can only take the shape of a double helix or briefly as an unstable single strand. Though it’s boring, the DNA molecule is much more stable, less reactive, and more compactable than RNA so it makes it more suitable for storing our precious genetic information.
RNA can take on some pretty awesome shapes, it can be folded in a million+ combinations. In fact, some people make their careers out of finding new possible structures of RNA. There’s even a game you can play to help researchers discover new shapes.
So, some of you may be asking: ‘why can’t C pair up with G? What happens if they don’t pair correctly?’. Well, without going into too much detail about all the different types of mutations (we’ll save that for another day) the mispairing of bases is called a ‘point’ mutation. Point mutations are usually fixed by molecular machinery and even if they remain ‘unedited’ they don’t often cause too many problems for the organism. Point mutations come in two different flavors: tranversions and transitions. Transition mutations are when a purine molecule is converted to another purine, so when a A changes to a G, these are usually less of a big deal as a purine and pyrimidine are still matched together, even if they don’t fit perfectly. A transversion mutation causes more issues as purines are converted to pyrimidine and vice versa, thus an A changes to a T. It’s easy to see how these simple mutations (which may have been due to a missing oxygen molecule) could lead to a big change in the DNA sequence. It’s like playing molecular telephone.