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See especially the section on Education Resources.
BioChemWeb
http://biochemweb.net/
A virtual library of Biochemistry, Molecular Biology and Cell Biology with detailed subject pages and extensive general resources.
The Cell: An Image Library
http://www.cellimagelibrary.org/
Peer-reviewed database of images, videos and animations showcasing cell architecture, intracellular functionalities, and both normal and abnormal processes.
The Protein Data Bank archive is the single worldwide repository of information about the 3D structures of large biological molecules, including proteins and nucleic acids.