NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,846 terms related to cancer and medicine.

Browse the dictionary by selecting a letter of the alphabet or by entering a cancer-related word or phrase in the search box.

The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein.

EnlargeStructure of DNA; drawing shows a chromosome, nucleosome, histone, gene, and nucleotide base pairs: guanine, cytosine, adenine, and thymine. Also shown is a cell and its nucleus.

Structure of DNA. Most DNA is found inside the nucleus of a cell, where it forms the chromosomes. Chromosomes have proteins called histones that bind to DNA. DNA has two strands that twist into the shape of a spiral ladder called a helix. DNA is made up of four building blocks called nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C). The nucleotides attach to each other (A with T, and G with C) to form chemical bonds called base pairs, which connect the two DNA strands. Genes are short pieces of DNA that carry specific genetic information.