Here's a breakdown:

* DNA: The genetic blueprint containing the instructions for building proteins.

* Transcription: The process of copying a segment of DNA (a gene) into mRNA.

* mRNA: A temporary copy of a gene that carries the instructions for building a protein to the ribosome.

Therefore, the main product of transcription is mRNA. However, other molecules involved in the process include:

* RNA polymerase: The enzyme that catalyzes the synthesis of mRNA from DNA.

* Ribonucleotides: The building blocks of RNA (adenine, guanine, cytosine, and uracil).

* Transcription factors: Proteins that help RNA polymerase bind to DNA and initiate transcription.

While the primary product of transcription is mRNA, other RNA molecules are also produced, such as:

* Transfer RNA (tRNA): Carries amino acids to the ribosome for protein synthesis.

* Ribosomal RNA (rRNA): Forms part of the ribosome, the site of protein synthesis.

However, the primary focus of transcription is to create mRNA to carry genetic information to the ribosome for protein synthesis.