PROF. W. VILLIGER / SCIENCE PHOTO LIBRARY PROF. W. VILLIGER / SCIENCE PHOTO LIBRARY
False-colour transmission electron micrograph of the human serum protein molecule C1q, part of the body's immune system. When an antibody combines with its antigen, it can trigger the destruction of the cell to which the antigen belongs, such as a bacterium - by using C1q. An antibody attached to a target cell binds to one of C1q's 6 "heads". This triggers a cascade of the 9 "complement" proteins, designated C1 to C9, which circulate in blood plasma. These proteins punch holes in the membrane of the target cell & destroy it. C1q consists of six identical subunits, each containing 3 polypeptide chains & a globular head. Magnification: x440,000 at 35mm size. Green tint. Original is tiny BW print P266/002 Ref: MICROCOSMOS, fig.
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