How can cells with similar DNA do such different jobs?

A nerve cell has long extensions for communication, while a muscle cell contains structures that produce force. Most cells in a person's body began with essentially the same inherited DNA. Their different jobs arise largely because they use that information differently.

A gene is a stretch of DNA whose information can contribute to a functional RNA or protein. Gene expression is the process of using that information. A cell does not use every gene equally all the time. Regulatory molecules affect which genes are active and how strongly they are expressed, changing the kinds and quantities of proteins the cell produces.

Proteins help build cellular structures, carry out reactions and receive signals. If a developing cell produces particular sets of proteins, its shape and capabilities change. Some sets support contraction, others communication, secretion or protection. Becoming a more specialized kind of cell is called differentiation. It is a gradual sequence of chemical and structural changes, not a cell deciding on a career.

Signals from nearby cells and the wider body help guide this process. A cell's position and its earlier history affect which signals it receives and how it responds. Regulatory patterns can also be maintained as cells divide, allowing descendants to continue performing a similar role. This stability helps tissues keep their organization while individual cells are replaced.

The same-DNA explanation needs qualifications. Cells can acquire mutations, and some specialized cells lose their nuclei; mature human red blood cells are an important example. Immune cells can also make specific DNA rearrangements associated with their functions. These exceptions do not change the broad principle that differences in gene use account for much cellular specialization. The amount of a protein matters as well as its presence, so gene activity is often adjustable rather than simply on or off.

The illustration uses colored bars to represent different amounts of gene activity, not different genes owned by each cell. Both example cells need many shared housekeeping functions as well as their specialized ones. A body can therefore build a remarkable variety of working parts without handing each part an entirely separate instruction collection. What matters is which information is used, when it is used and how the cell's surroundings help regulate that use.