Matthias Schleiden (left) and Theodor Schwann (right) separately proposed that plants and animals were composed of individual units called cells, and that these cells were combined to form tissues, organs,
and organ systems.
Virchow would further cement the concept of the cell theory by proposing
that all cells arise from other cells. This would eventually link
the concept of biogenesis with heredity, since the living cell must, if
it is to give rise to others like it, carry some immutable substance which
guarantees its ability to do so.
the 1930s, Linus Pauling demonstrated the physical laws which govern the
arrangement of atoms within molecules when he proposed the structure of
the protein molecule. At the same time, J. Desmond Bernal began the
use of X-ray crystallography to examine protein structure. Later,
Pauling, Rosalind Franklin and others would utilize this technique in their
studies which attempted to describe the shape of the DNA molecule.