Chemistry Reference
In-Depth Information
a
b
d
c
e
f
g
h
Fig. 3 Examples of mechanical bonds in nature. (a) X-ray image of human vertebrae, which
protect the spinal cord with mechanical bonds. (b) A turtle's shell has a similar function to the
spine, but protects more organs. (c) Electron micrograph of a DNA catenane [
29
]; scale bar: 1
m
m.
(d) The crystal structure of
-exonuclease, paired with a model depicting how it encircles DNA
while catalyzing its hydrolysis [
30
]. (e) “Protein chainmail”: the crystal structure of the bacterio-
phage HK97 capsid, highlighting catenated protein macrocycles [
31
]. (f) Cartoon and model of
nanotubes that participate in mitochondrial scission [
32
]. TEM images show mitochondria before
(g) and after (h) constriction of the mechanically bound protein nanotubes; scale bars: 50 nm.
Reproduced with permission from [
29
] (copyright 1980 Elsevier), [
30
] (copyright 2003 Oxford
Univesity Press), [
31
] (copyright 2000 AAAS), [
32
] (copyright 2011 Nature Publishing Group)
l
structures in basic biological processes such as DNA recombination and replication
as mediated by various enzymes [
36
]. Many topological DNA structures have now
been imaged [
29
] quite beautifully by electron microscopy (Fig.
3c
).
