What Is DNA, and What Is the Genome?

DNA is the chemical that carries genetic information. The genome is all the genetic material of an organism. A gene is a small section of DNA, so a genome contains an organism’s genes as well as the rest of its DNA.

How is DNA organised?

DNA is a polymer: a long molecule made of repeating units. It consists of two strands twisted into a shape called a double helix. In most human cells, DNA is packaged into structures called chromosomes, which are found in the nucleus.

A gene is a section of DNA on a chromosome. It codes for a particular sequence of amino acids, which are joined to make a specific protein. Proteins help determine how cells work and can affect an organism’s characteristics.

For example, one chromosome carries many genes. One gene codes for the amino acid sequence of a particular protein, while another codes for a different protein. Both genes are sections of DNA, but neither is the whole chromosome or the whole genome. That is why gene and DNA do not mean the same thing.

Why does the genome matter?

Studying the human genome can help scientists search for genes linked to diseases and improve their understanding and treatment of inherited disorders. It can also help them trace patterns of human migration in the past.

The genome means the entire genetic material of an organism, not just the DNA linked to one characteristic. Remembering that distinction helps when a question uses several of these terms together.

For an exam answer, keep the scale clear: DNA is the molecule; a gene is a section of that molecule; a chromosome contains DNA; and the genome is the organism’s entire genetic material. The common mistake is to say that the genome is just one gene or one chromosome. It means the whole set, not a single part.

These definitions apply to both Foundation and Higher tier in AQA GCSE Biology.