Structure and function of deoxyribonucleic acid (DNA)

Deoxyribonucleic acid (DNA) is the information-carrying molecule found in all living organisms. In most animal, plant and fungal cells DNA is stored in the nucleus coiled up in thread-like structures called chromosomes.

The nucleus of one of your skin cells contains about two metres of DNA, so a chromosome is a very large molecule compacted into a very small space.

The structure and function of DNA: a human with a magnifying glass showing a cell.  The cell is then magnified to show a chromosome, which is magnified to show the DNA strand.

The information DNA contains is the instructions that the cell uses to make proteins. Proteins play a big part in determining the characteristics of specialised cells and whole organisms.

Your eye colour, muscle mass, height and even your ability to learn new skills all result from the activity of specific proteins. The building blocks of DNA are called nucleotides.

There are four different types of nucleotide. The part of a nucleotide that can make it different from others is called the base.

Nucleotide base: four ribose, stacked vertically.  To the left these inter-connect with proteins.  To the right of the bottom ribose is a box saying "G", to the left of the next ribose is a box saying "C", next is "U" and finally "A" at the top right.

The four DNA bases are adenine, thymine, cytosine and guanine. These base names are abbreviated to A, T, C and G.

Nucleotides with different DNA bases. Adenine has a triangle cut out of its rhs, thymine has a triangle added to its lhs.  Guanine has crescent removed from lhs and cystosine has one added.

Nucleotides are linked together to form strands. DNA consists of two strands of nucleotides twisted around each other to form a shape called a double helix.

Nucleotides join together to form twisted strands around each other to form a double helix

The two strands are held together by weak bonds between pairs of bases. Only certain pairs of bases have complementary shapes that let them form bonds with each other to make the double helix.

Base A bonds with base T and base G bonds with base C. These are complementary.

Certain pairs of bases have complementary shapes that form bonds to make the double helix. Adenine and thymine bond as do cytstosine and guanine.