the role of dna - chains of information

         The astounding and compelling neatness of the structure of DNA is that it contains a built-in mechanism for information transfer. DNA strands are capable of self-recognition and self-replication. Duplication of the genetic information takes place every time a cell divides. This means that information encoded in the structure can be passed from one generation to another. Parent DNA molecules can replicate to produce identical daughter copies.

         The structure of DNA is also used in nature to store the blueprint for the synthesis of proteins. Broadly speaking, the amino acis sequence of each polypeptide chain is encoded on a specific stretch of DNA (a gene). The code in a gene is used to make copies of a particular polypeptide chain through a two-stage process.

• Transcription: the DNA template is first copied (transcibed) into an intermediate nucleic acid molecule, messenger ribonucleic acid (mRNA).

• Translation: mRNA molecules programme the assembly of the polypeptide chain, involving ribosomes attaching to, and moving alone.

          Thus DNA, by the processes of transcription and translation, is ultimately responsible for the structure of all the proteins synthesised by cells. So, to reiterate, DNA both preserves the genetic information (replication), and directs the sysnthesis of proteins (transcription and translation). This is sometimes referred to as the «central dogma of molecular biology».

         DNA molecules are enormous macromolecules. They need to be, as the DNA contains the essential genetic information that defines the organism concerned.

        The folding of such lengths of DNA into the compact chromosomes that become visible under a light microscope at cell division represents an amazing feat of packaging. It also emphasises the enormity of the problem tackled by the Human Genome Project in mapping human DNA. Another point to note is that only a small proportion of all of this DNA codes for proteins. The remainder is a mixture of «junk» and sections that regulate the decoding itself. The fuctional regions of DNA are known as genes.