The aim of gene therapy is to replace faulty genes with fully functional copies, and thus correct the problems caused by mutations.  Similarly, the aim of genetic engineering is to insert useful/beneficial genes into cells that do not already have those genes.

In both cases, the focus is on DNA because it’s a much more stable molecule.  RNA and proteins are degraded over time, thus giving the target cell either of these molecules would not produce a lasting effect.

 

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There are two major challenges that both fields have to overcome:

The first challenge involves just getting that new DNA molecule into a target cell.  Cells are very selective in the types of molecules they allow to enter, and they do not take up large molecules (like DNA) into their interior.

Research into methods used by viruses and other biological entities, which are known to be very efficient at inserting DNA into cells, is helping us address this challenge.

Once that first challenge is overcome, the second challenge involves inserting the foreign DNA molecule (provided by the scientist) into the cell’s genome.  If the new gene is not integrated into the genome, then it will be lost when the cell divides.

One of the major problems with this, is that in most species, it is very difficult to insert the foreign DNA into a specific location in the genome.  As a result, in most such attempts, the new DNA is inserted fairly randomly into the target genome.  This random insertion has the potential to disrupt/mutate other genes in that cell.

Engineering a cell that contains the desired DNA sequence, in a location that does not disrupt any known genes or other important sequences, is therefore extremely time-consuming and expensive.

The discovery of the CRISPR/Cas9 system in bacteria has the potential to help science overcome this limitation.  In order to gain an understanding of how this system works and its potential, we will first need to learn a little about viruses and bacteria.

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Comprehension Question