"Although it may look complicated, the DNA in a cell is really just a pattern made up of four different parts called nucleotides. Imagine a set of blocks that has only four shapes, or an alphabet that has only four letters. DNA is a long string of these blocks or letters. Each nucleotide consists of a sugar (deoxyribose) bound on one side to a phosphate group and bound on the other side to a nitrogenous base.

There are two classes of nitrogen bases called purines (double-ringed structures) and pyrimidines (single-ringed structures). The four bases in DNA's alphabet are:

  • adenine (A) - a purine
  • cytosine(C) - a pyrimidine
  • guanine (G) - a purine
  • thymine (T) - a pyrimidine" (Citation 20)

Adenine pairs with thymine and cytosine pairs with guanine. Anything else and it becomes a mutation. 
DNA comes in a shape known as double helix, which is basically a twisted ladder.

Structure of DNA. (Image 22


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