DNA Structure

Topic 3.3

3.3.1 & 3.3.2: DNA nucleotide structure

DNA nucleotides are made up of a sugar (deoxyribose), base (adenine, guanine, cytosine, thiamine) and phosphate.

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DNA nucleotide structure

3.3.3: How are DNA nucleotide joined together?

DNA nucleotides are joined together in a condensation reaction which produces water and a covalent bond between the two nucleotides. The figure below illustrates a condensation reaction between two DNA nucleotides. These reactions are continued until a single-strand of DNA is composed.

Nucleotide Condensation
Structure of a DNA strand

3.3.4 & 3.3.5: How is a DNA double helix formed?

The DNA double helix is formed by using complementary base pairing (i.e., adenine bonds thymine and cytosine bonds guanine). In the figure below key points include complementary base pairing held together by hydrogen bonding in the sugar-phosphate backbone.

DNA structure
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