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module:DNA: Structure and function

page:How RNA controls cells

DNA is copied only when a cell needs to duplicate itself. RNA is made by copying sections of DNA and occurs throughout the lifetime of a cell. In some cases, such as with human nerve cells, this could be throughout our entire lives.

When DNA replicates, the entire genome is copied. But the 'messenger' molecule does not need all of this information, and only a small part of the DNA information is duplicated. Only one of the strands of DNA contains the genetic code that is the right way round and this is the one that transcribes into RNA.

The other strand of DNA is a mirror image of the gene and 'floats' free while RNA is synthesised; the two strands twist back together into the double helix when the new molecule is complete.

The RNA molecule

RNA is read in groups of three bases, by specialised molecules that assemble amino acids into proteins. RNA is composed of the sugar ribose rather than deoxyribose, and one of the four nucleotide bases is different. The adaptor molecules convert the nucleotide 'language' of RNA into the amino acid 'language' of proteins. The RNA base Uracil functions as if it were the DNA base Thymine. So, as expected, DNA base C pairs with RNA base G and DNA base T pairs with RNA base A, but DNA base A pairs with RNA base U. The 'language conversion' process of protein synthesis is also known as translation.

When complete, RNA molecules move out of the nucleus and into the main body of the cell. Here, the RNA base sequence is 'read' in groups of 3 (eg UUC, ACG) that correspond to bases in the cell, which represent amino acid molecules. When these groups of amino acids connect they become proteins that build, maintain and manage specific cellular activities. This process is called protein synthesis.

Proteins are the most versatile and powerful molecules in the body. These molecules can be enzymes, hormones and antibodies. Your hair, nails and skin are made of protein.

There are many scientific developments that rely on altering a cell's RNA rather than DNA. For example, some new cancer treatments aim to interfere with tumour cell RNA replication. There is also a method of producing decaffeinated coffee by creating genetically modified coffee plants by interfering with the production of RNA which leads to caffeine production!

Try this RNA building activity to see exactly how RNA synthesis takes place.



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