基因的组织结构

Along with the complex arrangement of genetic material in a cell's nucleus, human genes also demonstrate their own unique organization.

Dispersed between the chromosomes are over 20,000 genes, sometimes separated by vast stretches of non-coding DNA, or that which does not encode proteins. Key to the organization of an individual gene is its promoter, to which machinery, especially RNA polymerase, can attach.

When this enzyme recognizes a nearby transcription initiation site, it begins to generate a strand of RNA, using DNA as a template. The polymerase then traverses the genetic material, and continues to yield RNA until it identifies a gene's transcription termination sequence, stopping the process.

Importantly, between these beginning and end points lie areas called introns and exons, both of which are reflected in the RNA product. However, subsequent processes remove introns from this transcript.

Since this RNA will be used to generate proteins, exons are denoted as coding regions, whereas introns are another example of non-coding material.

Interestingly, other types of non-coding DNA like silencers also associate with genes. Proteins called repressors bind to these regions, preventing polymerase-promoter association, inhibiting transcription. As a result, silencers help to regulate gene expression.

Thus, a gene consists of various components. Among them a promoter, exons, introns, and regulatory elements, which together help to determine protein expression in a cell.