DNA molecules are large and complex. They carry the genetic code that determines the characteristics of a living organism.

The backbone of the DNA double helix consists of alternating phosphate and deoxyribose sugar molecules.

Interlinking bases hold the two sides together.

DNA structure

Four different bases exist in DNA:

  • A = adenine
  • T = thymine
  • C = cytosine
  • G = guanine

As A is complementary to T and C is complementary to G they pair up.

This is known as the base-pairing rule.

A nucleotide consists of 1 phosphate, 1 sugar and 1 base.

Each individual's DNA is unique.

Apart from identical twins, no one shares the same sequence of bases.

The DNA code

DNA works by providing a code for cells to make a particular protein (for example, an enzyme).

The DNA code (sequence of bases) is found on the coding strand.

Three bases (a base triplet) code for one amino acid.

Amino acids are then joined in this order to make the protein.

It is important that the correct base triplets are arranged in the correct order along the coding strand.

This is known as the base triplet hypothesis.

Genetics base triplets

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