Cytosine and guanine are destined base pairs in DNA. So, how do the base pairs know who goes together? The answer lies in the hydrogen bonds that they share. Adenine and thymine are held together by two hydrogen bonds, but cytosine and guanine are held together by three bonds. Scientists have observed that DNA with more guanine and cytosine pairs is more stable; however, it’s not because of these triple hydrogen bonds that hold DNA together, it’s that GC pairs tend to have better stacking interaction. This term describes the weak bonds or Van der Waal forces that stabilize a molecule. More stability means that the molecule will stay intact longer when heated.
GC content in the Genome
Throughout an organism’s genome, scientists can see patches of high GC content. Usually, this means that these regions include some sort of protein-making sequence. It makes sense, evolutionarily, that the stablest gene will be the one that has a better chance of surviving. Ignoring the obvious – your organism not being able to reproduce – an unstable gene sequence could quickly mutate to code for a useless protein. Or a protein that could kill the organism. Yikes!
All Organisms have GC Pairs
Since both cytosine and guanine are needed in order to code for many amino acids, it’s impossible to have organisms that have 0% or 100% GC content. Plasmodium falciparum is a unicellular parasite (the one that causes malaria) has the lowest GC content at about 20%. The human genome by contrast has about 40% GC content. By looking at how and when organisms acquired more GC content into their genome, scientists can use this as yet another way to see the evolutionary relationship between species.
What Exactly is G and C?
G stands for guanine and C stands for cytosine. You know guanine as the white material found in the droppings of birds and bats. In fact, the word guano is Spanish for “droppings”. Guanine is also responsible for the reflective property in the eyes of certain animals, such as alligators. Cytosine also has an interesting story in that this nucleotide can spontaneously change to uracil. We have evolved uracil glycosylase which cuts out uracil in DNA. Cytosine is also the only nucleotide that scientists have NOT found in meteorites, leading many to see this as a piece of evidence for the RNA world theory.
Get G and C
If you love the pairing of guanine and cytosine, then you’ll probably also love to wear the pair. At our store, you’ll find CG mix and match earrings, CG pair necklace, or wear the nucleotide necklace all by itself. You can also choose to match your GC piece with any of the pieces in our DNA and RNA collection or adenine-thymine collection. Buy these pieces for yourself or for a friend. They also make great gifts for biochemists, bacteriologists, geneticists, and starry eyed research students.
written by Science with Evie