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Since 1953 (when the helix structure of DNA was discovered) we step by step got to know more and more about DNA. A relatively small part of our DNA contains recipes for proteins, but that doesn't mean a large part of the DNA is 'junk' (discarded left-overs of evolution). More and more functions of this formerly called junk DNA are discovered. And the recipes are used in a creative way....
More on DNA can be found on DNA-2
Above a schematic (simplified) representation of what we call "alternative splicing"
Extra genes and programmes
Sometimes large quantities of certain proteins are needed: the genes involved often have some copies in the DNA to be able to work faster. Mutations in such genes usually don't have any effect: enough working copies remain. This also means natural selaction doesn't work on these genes.
For many important characteristics back-up systems exist in the genome: if one programme gets damaged, another one can take over. Monophylists state that such redundant (superfluous) genes came into being by duplicating genes which could easily mutate to get new characteristic because natural selection doesn't work in it. This theory can be checked by three predictions:
DNA is like a library with basic recipes, with built-in variation options. Think of a birthday cake. The one shown above has three layers, which means three varieties of the recipe.. Ingredients are mixed per recipe, you bake each of the layers and fillings, different icings, cream, cherries and birthday candles complete the cake.
In much the same way a DNA recipe (RNA) first will be edited, subsequently translated into a protein chain, folded into the right shape and put together with other proteins, sugar chains and possibly other chemicals before it's ready to be used in the cell. And we haven't spoken about transport and the like yet ...
How does DNA work?
During metamorfosis from egg to caterpillar to butterfly the Swallowtail (see pictures above) uses different sets of genes. That's easy to understand for butterflies (because they change from leaf eater without sex organs into nectar eater with reproductive urge), but in our bodies it's much the same. There is nog stage in our lives where we use all of our DNA, but every cell contains the whole library.
A relatively small part of the DNA has genes that code for proteins. These genes are regulated by other genes: some of these code for regulating proteins, others for regulating RNA. Another part of the DNA is used to code for transport-RNA and ribosomal RNA (helps to build proteins).
Splicing was discovered in the seventies: each gene in the DNA appears to 'much too long' and after copying pieces of the m-RNA are cut out before the gene is translated into a protein chain. But this cut-and-paste operation happens in different ways in different organs (sometimes eight varieties are possible), so regulatory genes etc. are necessary to do this properly (taking care your brains don't turn into a liver e.g.).
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