ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
DNA molecule and red blood cells. Computer artwork of a molecule of deoxyribonucleic acid (DNA, blue) and red blood cells (erythrocytes). DNA is composed of two strands twisted into a double helix. Each strand consists of an outer sugar- phosphate backbone (thick blue line) with nucleotide bases attached (lines inside helix). There are four different bases: guanine, cytosine, thymine and adenine. Guanine always pairs with cytosine and adenine always pairs with thymine. DNA contains sections, called genes, which encode the body's genetic information. Genes determine each cell's structure, function and behaviour. Mature red blood cells are the only cells not to contain DNA.
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