Genetics: Gene Expression

Genes are transcribed into RNA by the process of transcription. Some RNA molecules are functional in and of themselves. Examples include the RNA components of certain enzymes (e.g., telomerase); transfer RNA (tRNA), which delivers amino acids to the ribosome for protein synthesis; and ribosomal RNA (rRNA), a structural component of the ribosome. Other RNA Figure 1 SOURCE: Author molecules are intermediaries in protein synthesis. Such RNAs are processed in the nucleus into messenger RNA (mRNA) molecules. mRNAs are then exported to the cytoplasm, where they bind ribosomes and direct synthesis of the encoded protein by the process of translation.

Genes are expressed when their ultimate products (RNAs or proteins) are produced. Sometimes, genes encoding proteins are considered expressed when they are simply transcribed, but it should be remembered that the proteins, not the transcripts, are the functional products.