Proteins are the workhorses of a cell; they catalyse biochemical reactions and maintain cell structure. They are synthesized from genes in our DNA, where each gene codes for a unique protein. So, how do we determine what role a protein plays in a cell?
There are a few different techniques we can use to establish this: siRNA gene silencing, gene knockout and gene mutation. Before making a protein, cells make a copy of the gene that codes for that protein, this copy is known as the mRNA. The mRNA then gets translated into the respective protein.
In siRNA gene silencing, a specially prepared RNA, the siRNA, is introduced into the cell. The siRNA is similar in sequence to the mRNA and with the help of a protein complex, RISC, it binds to its target mRNA. The siRNA/mRNA complex is a signal for degradation; hence it is subsequently broken down by the cell’s degradative enzymes. As a result, the protein of interest is not made. Another method used to prevent protein synthesis is gene knockout. It is a technique in which the gene itself is made inoperative. This is done by introducing an artificial gene, similar to the gene of interest, into the cell. Once in the cell, the cell’s own DNA repair machinery swaps out the gene of interest with the artificial gene. The artificial gene contains an altered sequence, so it makes an inactive form of the protein or none at all.
Yet another way of studying protein function is by introducing mutations. Mutations are small changes in a gene, made using drugs or UV light. Altering the gene alters the mRNA, which subsequently alters the protein’s function or synthesis. In all these cases, by preventing protein synthesis or disrupting its function we can observe its subsequent effect on the cell and thereby determine the protein’s role. For example, if cell shape is altered upon a protein’s deletion, it suggests that this protein is involved in maintaining cell structure.