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Structure of DNA

A nucleotide is made up of 3 things. A nucleotide is one little "rung" of the ladder that forms a DNA base sequence.

A nucleotide is made of a phosphate group, a sugar (deoxyribose) and an organic base.

Organic bases can be split up into 2 groups -

  • Single-ring bases, they are cytosine and thymine
  • Double-ring bases, they are adenine and guanine

The phosphate, deoxyribose and organic base all forms due to a condensation reaction, which forms one nucleotide (mononucleotide). If a condensation reaction occurs between one mononucleotide and another mononucleotide, this forms a dinucleotide. This can carry on onto a polynucleotide.

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Joining of Bases

Bases are complementory to each other because of the size of the molecule. As the double ringed bases are longer than the single ring bases, the double ringed bases must go with each other. Therefore adenine is complementory with guanine. And cytosine is complementory with thymine.

Double ringed bases always bond with 3 hydrogen bonds, where single ringed bases only bond with 2.

The phosphate group always alternates with the deoxyribose group in the DNA structure.

Deoxyribose sugar's structure is a pentagon, where the phosphate is circular. The base always comes from the top corner of the sugar.

For each turn of a complete double helix, there is 10 bases

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Function of DNA

  • Hereditary Material
  • Passes on genetic information from one cell to the other
  • There is almost an infinate amount of sequences you can have with DNA, explaining the huge genetic diversity within living organisms

How DNA adapted -

  • It is stable, can pass on from generation to generation
  • The 2 strands can be seperated during DNA replication/protein synthesis
  • Large, carrying a large amount of genetic information
  • The bases are protected by the outside chemicals (phosphate, deoxyribose)
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