 So, nucleic acids. Nucleic acids are macromolecules that are polymers. Polymers means that their components are monomers and they have something in common, right? So, nucleotides are the monomers of the nucleic acids. The name nucleic acid comes from the fact that they were first isolated from the nucleus of the eukaryotic cells. However, nucleic acids are present outside of the nucleus as well. Now, this is the basic structure of the nucleotides. As you can see, what they have in common is a phosphate group, is a pentose sugar, sugar that has five carbon atoms, and that pentose sugar could be deoxyribose, in the case of DNA, or it could be ribose in the case of ribonucleic acid, or RNA. And, nitrogenous base that is either one of these four for DNA or uracil in the case of ribose together with adenine, and guanyin and cytosine for RNA. You have heard about DNA as base of life on Earth, and RNA as well. Let's see what are the differences between them. So, double helix is the feature of the DNA in most of the cases. The exception to the rule are some viruses that may have a single-stranded DNA. Ribonucleic acid in most of the cases are single-stranded. However, some viruses have double-stranded DNA, and sometimes in our own body, like for instance, transfer RNA and have parts that are double-stranded. This is how they're pairing. So, timing and adenine, they are forming two hydrogen bonds between them. Guanyin and cytosine are forming three hydrogen bonds between them. The rest of it is a sugar phosphate backbone. So, how they're paired is that these are the bonds that are making the polymer, and the three are bases that are there to combine with other strands. And we will learn more about it during the translation and transcription process, how it works.