The DNA of a cell makes up its “genome.” This genome contains a set of instructions describing how the cell can deal with various situations, but the DNA doesn’t actually perform any of the functions of a cell – that is done by proteins and enzymes (a specific category of proteins).
In order to understand gene expression, it may help to think of the genome as a book inside a reference library. In a reference library, you can read and copy parts of books, but you can’t take them out. Similarly, the DNA in a cell is read, and relevant parts of it (the genes) are copied for use.
The copying is accomplished by using the same principles that govern DNA replication. In DNA replication, one DNA strand acts as a template for the formation of a new strand. Similarly, when a cell wants to “express” a particular gene, it opens up the relevant region of the DNA and uses one of the strands to make a copy of it into a related molecule called RNA. This process is referred to as transcription and produces a molecule called messenger RNA (mRNA for short).
This message can then be used to produce many copies of the functional component of a cell – a protein. This process of converting an RNA message into a protein is called translation.
The term “translation” is quite appropriate. The genetic code, composed of combinations of four different nucleotides, has to be converted (or translated) into a sequence of amino acids (the building blocks of a protein).
Comprehension Question