* Genetic blueprint: DNA contains the genetic instructions for building and maintaining an organism. It acts as a blueprint for the cell, dictating everything from protein production to cellular processes.

* Heredity: DNA carries the genetic information that is passed down from one generation to the next. This ensures that offspring inherit traits from their parents.

* Cellular function: DNA is the basis for the production of proteins, which are the building blocks and workhorses of the cell. It directs the synthesis of proteins that are necessary for a vast array of cellular functions, including metabolism, growth, and repair.

Exceptions:

* Mature red blood cells: These cells in mammals lose their nucleus during development, and thus lose their DNA. However, they are not considered "true" cells, as they are unable to reproduce or carry out many essential cellular functions.

* Viruses: While viruses do contain genetic material, they are not technically considered cells. They lack many essential cellular components and rely on host cells to reproduce.

In essence, DNA is the fundamental molecule of life, and its presence is crucial for the existence and functioning of all cells.