JAMES M. HOGLE, HARVARD MEDICAL SCHOOL / SCIENCE PHOTO LIBRARY JAMES M. HOGLE, HARVARD MEDICAL SCHOOL / SCIENCE PHOTO LIBRARY
Polio virus. Molecular graphic of a polio virus. The outer protein coat (capsid) of the polio virus is roughly spherical and measures 25-30 nanometres in diameter. It consists of 12 repeated pentagonal units, each of which consists of four different proteins (red, blue, green and yellow). The blue protein marks the centre of each pentagon. The tiny spheres represent individual amino acids. The capsid is highly resistant to heat and acid, making the virus stable in such harsh environments as sewage systems and the human gut. Infection is by the faecal-oral route, and may lead to the paralysing disease poliomyelitis.
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