KENNETH EWARD / SCIENCE PHOTO LIBRARY KENNETH EWARD / SCIENCE PHOTO LIBRARY
Computer model of a molecular beacon probe (white) in its native state (bottom left) and hybridised (top right) with a strand of DNA (deoxyribonucleic acid, blue). These probes are used to detect specific sequences in a sample of DNA. The probe consists of a length of single stranded DNA that contains a sequence complementary to the target sequence between complementary ends that anneal to one another, forming a loop. On one end of the probe is a fluorophore (fluorescent dye molecule, blue ball), on the other a quencher (green ball). When the complementary ends are in close proximity the quencher prevents the fluorophore from fluorescing. When the probe is hybridised to its target sequence the fluorophore and quencher are separated, allowing the fluorophore to fluoresce and signal that hybridisation has occurred.
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