DNA's Structure
Introduction - MAIN
DNA's are polymers made up of monomers known as nucleotide. DNA has double helix structure since there are two strands of nucleotide.
Nucleotide
The 5 major nucleotide - Cytosine, Thymine, Uracil, Adenine, and Guanine - are categorised into 2 major categories, the purines [9 carbon] - Adenine and Guanine - and pyrimidines [5 carbon] - Cytosine, Thymine, and Uracil. Cytosine bond only with Guanine (Car on the Garage) and Adenine only bond with Thymine (Apple on the Tree) - In RNA, Adenine bonds only with Uracil. Since Thymine is energetically expensive to create (because of the methyl group), Uracil is used in RNA.
3 Major Parts of Nucleotide
The Nucleotide have 3 major parts - The Phosphate Group, The Pentose Sugar, and the nitrogenous base. The phosphate group is the backbone of the DNA, along with pentose sugar which helps as a bridge between phosphate group and the nitrogenous base. Since Phosphate group wants a hydroxyl group to bond to and nitrogenous base needs carbon to bond to, Sugar is the best option found by nature and mankind.
Mnemonics (I made it)
There is an easier way to remember such parts. DNA's full form is Deoxyribonucleic acid. Deoxyribo- part mentions about sugar (The sugar in DNA is deoxyribose), -nucleic part mentions about the nitrogenous part, and acid part mentions phosphate group (The phosphate group make the DNA acidic).