Transcription in cells is the process where genetic information encoded in DNA is copied into messenger RNA (mRNA). This process begins when RNA polymerase binds to a specific region of DNA, unwinding the double helix. The enzyme then synthesizes mRNA by adding complementary RNA nucleotides to the growing strand. Transcription is crucial for gene expression, as the resulting mRNA transports the genetic code from the nucleus to the ribosomes, where it serves as a template for protein synthesis.