DNA:  Detailed View

DNA is composed of a sugar-phosphate backbone and nitrogenous bases:

• sides of ladder are made of a deoxyribose sugar and phosphate backbone
• rungs of ladder are made of pairs of nitrogenous bases
• there are only four bases:
  • A = adenine
  • C = cytosine
  • T = thymine (in RNA, the base U = uracil is used instead of T)
  • G = guanine

A nucleotide is one of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of a base (one of four chemicals: adenine, thymine, guanine, and cytosine) plus a molecule of sugar and one of phosphoric acid.

The two strands of DNA are antiparallel; they are parallel to each other but are oriented in opposite directions.

Each strand of DNA is read in a specific direction, from its 5' (five prime) end, to its 3' (three prime) end. How can you figure out which end is which? See the next slide...

Source:  image from the National Human Genome Research Institute (NHGRI) Genetic Illustrations; definition of nucleotide from the National Human Genome Research Institute (NHGRI) Glossary of Genetic Terms