Are both sides of DNA used?

Yes, both sides of DNA are used in the process of gene expression. The two strands of the DNA double helix serve different roles: one strand, called the template strand, is used during transcription to synthesize messenger RNA (mRNA), while the other strand, the coding strand, has the same sequence as the mRNA (except for uracil replacing thymine). Additionally, during replication, both strands are unwound and serve as templates to produce two identical DNA molecules.