It is important to note that unlike DNA, mRNA and proteins are short-lived molecules – they are degraded by the cell over time. In this way, a cell can express particular genes only when they are required.
The proteins and enzymes that are produced by translating the RNA message are the molecules responsible for actually carrying out the functions encoded by the genes.
Enzymes are proteins that participate in various biochemical reactions. For example, a variety of enzymes are involved in extracting energy from food, or synthesizing RNA or DNA. The remaining proteins tend to be molecules that are more structural in nature (ie. proteins that give the cell its shape).
Both types of proteins are composed of subunits called amino acids, and it is the sequence of these subunits that determines the function of the protein/enzyme. More specifically, the chemical properties (ie. charge, polarity, affinity for lipids) of the amino acids and the order in which they are attached to each other, give each type of protein/enzyme a specific 3D shape which is essential to its function.
In essence it is the sequence of the A,T, C and G-s in the DNA that determines the shape and therefore the function of a protein.
Mutations are changes in DNA sequence, and such changes can cause serious health problems. Sometimes those changes occur within the sequence of a particular gene. In these cases, a change in the DNA sequence will result in changes in the mRNA sequence, which could result in changes to the amino acid sequence of the resulting protein.
Since the amino acid sequence affects the 3D shape and function of a protein, a change in the protein sequence could easily affect the ability of the protein/enzyme to function properly.
Here are just a few examples of diseases where a simple change in the DNA sequence has a significant impact on the ability of the encoded protein to function properly:
Comprehension Question