Describe the structure of DNA

Firstly, when answering an IB essay question, remember that you are noted through key words or concepts. I will put these in italics and then explain them. DNA is composed of nucleotides, each nucleotide contains one deoxyribose (pentose sugar backbone), a phosphate, and one of four nucleotide bases (draw diagram to explain structure). The pentose backbone is composed of five carbon atoms, which are noted from 1 to 5 in the following way: C1, C2, C3... (show order in diagram). The phosphate is attached to the C5 carbon, while the base is attached to the C1 carbon. A nucleotide bonds to another by bonding its phosphate to the C3 atom of another pentose sugar in a covalent bond. This is why the direction of the strands are noted as 5' or 3': the 5' end is the end of the strand attached to a phospahte, while the 3' end is the end of the strand which is not attached to another phosphate, leaving the C3 carbon exposed (although it does bond to an OH). There are 4 types of nucleotide bases that can be attached to the C1 carbon: adenine (A), thymine (T), cytosine (C), and guanine (G). These base pairs are complementary, which means that they can bond with one another in the following way: A with T, C with G. The bases form hydrogen bonds between one another, AT forms 2 hydrogen bonds, while CG forms 3 hydrogen bond (show all of this through diagram). This is why we can say that DNA is a double helix composed of two complementary antiprarallel strands: As we can see in diagrams, DNA is composed of two strands, which are twisted in a helix due to the charges of it's components, and these strands are antiparallel as their bases are complementary and allow the two strands to bond through hydrogen bonding.