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Nucleotides v(sound)

Nucleotides are the result of the connection through covalent bonding of three different molecules.One of pentose (a five carbon atom saccharide), one of phosphate acid and one of an organic nitrogen containing basis.


DNA nucleotides contain the pentose deoxyribose and they are called deoxyribonucleotides.

On the other hand RNA nucleotides contain the pentose ribose and they are called ribonucleotides .


The nitrogen containning nouclotide-bases are adenine (Α) , thymine (T) , guanine (G) , cytosine (C) and uracil (U).

adenine
thymine
guanine
cytosine
uracil

Adenine , guanine and cytosine exist in DNA and RNA as well.On the contrary thymine exists only in DNA , while uracil only in RNA.

Two monophosphate nucleotides are bonded through covalent bond to form a dinucleotide. If another nucleotide bonds to the dinucleotide, a trinucleotide will be formed.The addition of a new nucleotide creates a tetranucleotide. When this procedure is repeated thousands times a polynucleotide is formed.In the DNA figure ,on the left, every nucleotide has been coloured differently.

 

Structure of DNA v(sound)

Polynucleotides and proteins, besides their primary structure, have also a specific configuration in space (3D-configuration). In 1953 J. Watson και F. Crick presented a model of DNA structure, which was named double helix model. Acccording to this model, which has been accepted from the entire scientific community, the molecule of DNA has the following basic characteristics :

It consists of two polynucleotides chains, the strands, which forme the double helix.

The nitrogen containning bases in each strand are vertical to the main molecule axe and extend towards its interior.

The two strands are being hold to each ather through hydrogen-bonds, which occur between their bases. Base pairs, between whom hydrogen-bonds can be formed, are defined as follows : adenine pairs to thymine and guanine to cytosine. Basis adenine /thymine and guanine/cytosine, are characterized as complementary. Between bases G και C three hydrogen -bonds occur, and between bases Α and Τ just two.

 

Biological role of DNA v(sound)

In a few words the DNA molecule is capable of:

  • Carrying the genetic information.
  • Controling through this information every cell activity.
  • Passing the genetic information unchangedfrom one generation to the next one.
  • Allowing the creation of genetic diversity.