DNA structure*

• DNA has a double helix structure, consisting of 2 strands of polynucleotides(DNA strands)
• the monomer of nucleic acid is a nucleotide.
• the monomer of DNA is deoxyribonucleotide
• the monomer of RNA is ribonucleotide
• DNA is deoxyribonucleic acid
• RNA is ribonucleic acid
• a nucleotide consists of a pentose sugar(deoxyribose/ribose sugar), a phosphate group, and a nitrogenous base
• RNA can have adenine, uracil, guanine, cytosine as nitrogenous bases
• DNA can have adenine, thymine, guanine, cytosine as nitrogenous bases
• the rule of complementary base pairing is that adenine bonds with thymine to form 2 hydrogen bonds, and guanine bonds with cytosine to form 3 hydrogen bonds
• pyrimidines consist of cytosine, uracil and thymine
• purines consist of adenine and guanine
• the pentose group in a nucleotide is bonded to 5C
• nucleotides are bonded to each other by phosphodiester bonds, between the 3C of a pentose sugar and a phosphate group
• a phosphodiester bond is a strong covalent bond formed between the 5' phosphate group of one nucleotide and the 3' OH group of another nucelotide. it is formed by a condensation reaction
• condensation reactions result in the loss of a water molecule
• the 5' end is the end with a phosphate group, and the 3' end has an OH group
• DNA has an anti-parallel structure, where DNA strands are arranged anti-parallel. One DNA strand runs from the 5' end to the 3' end while the other strand runs from the 3' end to the 5' end
• in double helix DNA, there are two antiparallel chains held together by hydrogen bonds between complementary base pairs (A-T & C-G)
• A bonds to T, forming 2 hydrogen bonds, while G bonds to C and forms 3 hydrogen bonds
• DNA is a polar molecule that deionizes in water to form a molecule with an overall negative charge. the phosphate group at the 5' ionizes to form PO4 2- ion and the 3' end OH group ionizes to form OH-, resulting in an overall negative charge
• nucleotides can only be added in the 5' to 3' direction. hence they can only be added to the 3' OH end
• DNA stability is conferred by, 1. the presence of strong covalent phosphodiester bonds between the nucleotides, which forms the strong sugar-phosphate backbone and ensures the stability of DNA and 2. the numerous hydrogen bonds between complementary base pairs. the presence of the multiple hydrogen bonds also helps confer DNA stability
• the existence of 4 varying nitrogenous bases allows DNA/RNA to represent a unique sequence that carries coded information held by the nucleic acid. Hence this diversity in base pairing allows DNA to store unique genetic information and hence, makes it suitable for storing information
• nitrogenous bases are bonded to the 1C of the pentose sugar
• the polymer of nucleic acid is polynucleotide