DNA, or deoxyribonucleic acid, serves a variety of purposes, including data storage and replication, in the human cell and in the cells of many other organisms. DNA in a human cell is primarily responsible for storing genetic information that is used to control almost every aspect of cellular expression. This genetic information is passed down from parents to offspring, resulting in offspring with some genetic traits of each parent. DNA in a human cell is also replicated whenever the cell divides; this ensures that each cell in the body has and expresses the same genetic information. DNA is also the first element in the synthesis of proteins, which are responsible for most cellular activity.

DNA in a human cell serves an essential role in biological inheritance, through which a child possesses some genetic traits of each of his parents. Humans reproduce through sexual reproduction. Most human cells contain two copies of the human genome so that, after cell division, both daughter cells will contain the same genetic information. Reproductive cells, one of which comes from each parent, contain only one copy. Two reproductive cells—one egg and one sperm—combine to form a human embryo containing a random assortment of genetic information from each parent.

Data storage and replication is one of the major roles of DNA in a human cell. Accurate copies of the human genome must be stored within each cell so genes can be expressed correctly. Mutations in DNA can cause the stored genetic information to be altered; this can cause altered gene expression that may lead to cancer or other diseases. DNA replication, then, needs to be a high-fidelity process; it happens countless times over the course of a human life and even minor errors in replication can cause harmful mutations. There are, accordingly, a variety of error-checking mechanisms in the DNA replication process that prevent nearly all possible replication errors.

Much of the genetic information contained in DNA in a human cell exists to be expressed as RNA or protein. In a process called transcription, double stranded DNA is converted to single-stranded RNA, or ribonucleic acid. Some forms of RNA can serve various cellular functions based on their molecular configurations, but most are translated into proteins. Proteins serve a tremendous variety of cellular functions, ranging from signaling to cellular regulation to the catalysis of biochemical reactions. DNA in a human cell, then, is responsible for the inheritance, replication, and expression of genetic information.