Studying Protein Function
Because proteins control almost every function of the cell, if we change one protein, look at the resulting physical effects on the cell, and compare them to normal cell functions, then we can determine the normal function of the changed protein.
To change a protein, you must first change the elements that make up the protein. Proteins are made of amino acids, which are molecules that are present in the cell but just sort of "float" around until called upon. DNA serves as the overall instruction manual to determine which amino acids will come together to form a protein. If you change an individual's DNA, you change the amino acid and thus the protein that is produced. Of course, the process of DNA to a protein is not so simple, but for our purposes, knowing the big picture is important.
Imagine DNA as the recipe for a protein. Just like if you were baking a cake, if you change the recipe, the finished cake will change, too! For example, if the recipe calls for 3 cups of sugar and you add 3 cups of salt instead, your "mutated" recipe will now produce a totally different concoction that will not be very sweet!
Below are examples of a normal amino acid sequence and the resulting protein, as well as what could happen to a protein if the amino acids are changed:
Now, let's see what happens to our sample protein when the Amino Acid Sequence changes!
We can see that mutating (e.g. changing) an organism's DNA produces different arrangements of amino acids, and therefore changes the overall proteins produced, including its shape, function, and how it interacts with other proteins! By manipulating cells, scientists can target and change specific proteins and observe the cells' physical response when the targeted proteins' normal functions are absent.
Of course, there are many ways to change a cell's DNA and affect the overall function of a cell. One of many methods for manipulating a cell and studying specific proteins is through cloning.