DNA

• DNA is made of two polynucleotide chains in a double helix structure
• two DNA polynucleotide strands join together by hydrogen bonding between complementary bases
• adenine always pairs with thymine
• cytosine always pairs with guanine
• the sugar-phosphate backbone holds the base pairings together, forming the double helix shape.
• there are always equal amounts adenine and thymine and equal amounts cytosine and guanine
• two hydrogen bonds form between A and T
• three hydrogen bonds form between C and G
• two antiparallel polynucleotide strands twist to form the DNA double helix shape