What are nucleic acids?
Nucleic acids store information that provide the directions for building proteins. The reason they are called nucleic acids is that they are situated inside the nuclei of eukaryotic cells. There are two types of nucleic acids: RNA and DNA. Our genetic material comes from DNA. Within DNA are genes, which program the amino acid sequences (primary structure) of proteins. These are encoded in DNA, and those cannot be read by proteins, so they must be translated into "protein language". This is done through RNA molecules translating the sequences.
Structure of nucleic acids
Nucleic acids are actually polymers of nucleotides. Nucleotides are composed of a nitrogenous base, a five-carbon ring, and at least one phosphate group. There are two types of nucleotides.
A pyrimidine is a nitrogenous base with only one ring (made up of Nitrogen and Carbon). These include Cytosine (which pairs with Guanine), Thymine (which pairs with Adenine and is only found in DNA), and Uracil (which pairs with Adenine and is only found in RNA). The name "pyrimidine" is based on "pyridine", which also has a hexagonal shape.
A purine has two rings, and there are only two nitrogenous base that are purines: Adenine, which pairs with Thymine/Uracil, and Guanine, which pairs with Cytosine. They are both found in both DNA and RNA. Purine, originally called "pure urine" has a pyridine along with an imidazole ring.
Structure of a Nucleotide
In the center, there is a five carbon sugar, deoxyribose in DNA and ribose in RNA. Connected to the sugar is a negatively charged phosphate group containing one phosphate and four oxygen atoms.
How are they linked?
Nucleotides are linked into long chains called polynucleotides, or DNA strands. Nucleotides are joined together by covalent bonds between the sugar of one nucleotide and the phosphate of another. This results in a sugar-phosphate backbone, which repeats sugar-phosphate-sugar-phosphate... . Nitrogenous bases (Adenine, Thymine ...) hang off the edge like appendages. Polynucleotides vary in length, from 100s of nucleotides to 1000s of nucleotides.
A molecule of DNA, or deoxyribonucleic acid, is double-stranded, with two polynucleotides wrapped around each other in order to form a double-helix. This looks like a coil, or a winding staircase, with each polynucleotide being a railing. The pairing is specific. In DNA, Adenine pairs with Thymine, and Cytosine pairs with Guanine. In RNA, Adenine pairs with Uracil. In DNA, the sugar is deoxyribose.
A molecule of RNA, or ribonucleic acid, is single-stranded. As stated before, there is an extra -OH in ribose, instead just an -H in deoxyribose. Deoxy ("without an oxygen") just refers to the one oxygen that ribose has that deoxyribose doesn't have. In addition, instead of thymine, RNA has uracil.