Re: What is the scientific definition of a gene in a DNA molecule?

Hello Quan,

Thank you for your question! In general, a gene is defined as the basic unit of heredity. In terms of molecular biology, a gene is a specific sequence of nucleotide bases (Adenine, Cytosine, Guanine, and Thymine are the four nucleotide bases found in DNA) which encodes a "recipe" for making a molecule (usually a protein) necessary for cell/organismal function. When a cell needs this particular molecule to be produced, the encoded genetic message is TRANSCRIBED from DNA into RNA, and then, usually, the RNA serves as a template for protein synthesis, a process also known as translation.

Genes are arranged end to end on chromosomes. Each human chromosome contains anywhere from several hundred to over a thousand genes. Because genes are transcribed selectively, as the need for them within the cell arises, the gene must encode not only the protein "recipe", but must also include information to help the molecules involved in transcription find and transcribe gene when needed. If you imagine a piece of DNA being "read" like words on a page, from left to right, your average gene is arranged as follows:

At the beginning of the gene sequence (far left) is a region called a promoter. This part of the code tells the transcriptional machinery of the cell where to begin making the RNA. To the right of the promoter is the region which will be transcribed. This region is made up of protein coding sequences called exons interspersed with non-coding sequences called introns. At the end of (to the right of) this code is a termination sequence that marks the end of the gene, and lets the transcriptional machinery know where to stop.

The process of transcription and translation is quite complicated, and is much easier to understand if you can look at pictures of this process. At the bottom of this message is the web address for a "Primer on Molecular Genetics" put out by the Department of Energy, which you might find helpful for starters. I would also recommend that you find an introductory text on molecular biology or genetics to help you begin to learn more about this topic. The scientist in charge of your project may be able to recommend one, or you could see what text the introductory Molecular Bio or Genetics course at your University is using. Good luck, and please feel free to write back if you have any more questions. I hope this will help to get you started.

Warm Regards,

Jen