Page 140 - Engineering in Nature

Engineering in Nature

they'll still fall apart. It calls for planning to arrange them in the right
way.
Of course, one tubulin molecule is attached to the next in a far
more complex way. There are thousands of different proteins in a cell,
and it is essential that the tubulin molecules attach themselves to the
right molecules. Were the tubulin molecules to join to just any nearby
protein, then the micro-hairs could never come into being.
The more we examine the design of the tubulin molecules, the
more complex its structure appears.
In this molecule, there are ten short, needle-like protrusions. At the
bottom are ten depressions in which these protrusions sit. A differ-
ence in just one of the protrusions would prevent the necessary tubu-
lin connection being made, which definitely proves that each tubulin
molecule is created to be compatible with another one.

The Connections That Enable the Hairs to Move
Examination of the cell reveals that like the tubulin molecules, the
micro-tubules are attached to one another. However, the connections
between the micro-hairs are not in the form of attachments, as is the
case with tubulin molecules. Micro-tubules can cling together only
with the help of other proteins, and there is an important reason for
this.

The movement of the micro-
tube is established by the con-
Nexin necting proteins among the
molecules comprising the
micro-tube. The main element
Dynein permitting movement is the
flexible nexin protein. When it
slides over the protein dynein,
Nexin this will transform into a bend-
ing movement.
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