DNA: The mystery of simplicity

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DNA is a winning formula for packaging genetic material. DNA in its simplicity is constructed by linking four different building blocks into a chain – a chain of four different nucleotides in different sequences. Two complementary chains combine with hydrogen bonds and form the well known double helix. 

The two strands of the double helix are anti-parallel, which means that they run in opposite directions.

A nucleotide is a combination of deoxyribose sugar, nitrogen base and phosphate. They differ in the nitrogen base present – either a purine (adenine or guanine) or pyrimidine (cytosine or thymine).

Almost all organisms – bacteria, plants, yeast and animals – carry genetic information encapsulated as DNA. One exception is some viruses that use RNA instead.

Exercise for scholars

 This is how a DNA double helix is put together.

 These are symbolic representations of the four nucleotides present in DNA. 

  • Draw these shapes, two of each, on a piece of card or stiff paper.
  • Cut out the 4 shapes with a scissors.
  • Arrange 4 different nucleotides in a chain by stacking the sugars on top of one another.
  • Now arrange a second chain next to the first one so that the hydrogen bonds link up correctly.
     

What you should notice:

  • The 2 chains run in opposite directions - anti-parallel.
  • A pyrimidine pairs only with a purine; A with T and G with C.
  • Only 2 pairs are found in DNA; AT and GC.
  • AT is paired with 2 hydrogen bonds.
  • GC is paired with 3 hydrogen bonds.