Final answer:
Side groups on a nucleotide are capped when building probes on a microarray to protect the nucleotide from degradation and ensure probe accuracy and stability.
Step-by-step explanation:
The side groups on a nucleotide are capped when building probes on a microarray in order to protect the nucleotide from degradation and to ensure the accuracy and stability of the probe. The caps added to the nucleotide prevent the ends of the RNA strand from degrading during the microarray experiment. They also help in the recognition of the probes by factors involved in protein synthesis, which is essential for the proper functioning of the microarray.