Biological Nanomachines Inspire Nanotechnology
Nano, nano; we’re hearing that morkish prefix a lot these days. It means 10-9 of something: most often, of meters (see powers of ten). A nanometer is a billionth of a meter. This gets down into the range of protein molecules and small cellular components. A DNA molecule, for instance, is about 20 nanometers across; an ATP synthase rotary motor is about 8 x 12 nanometers, and a bacterial flagellum about 10 times larger. Now that imaging technology is reaching into realms of just a few nanometers, scientists are keen to understand nature’s engineering in hopes of doing their own.
The premiere issue of Nature Nanotechnology made its debut this month.1 It contains a centerpiece review article by Wesley R. Browne and Ben L. Feringa entitled, “Making molecular machines work.”2 Though the article focuses on human progress and potential in the world of nanotechnology, it contains numerous ecstasies about biological machines unmade by human hands:
- Consider a world composed of nanometre-sized factories and self-repairing molecular machines where complex and responsive processes operate under exquisite control; where translational and rotational movement is directed with precision; a nano-world fuelled by chemical and light energy. What images come to mind? The fantastical universes described in the science fiction of Asimov and his contemporaries? To a scientist, perhaps the ‘simple’ cell springs more easily to mind with its intricate arrangement of organelles and enzymatic systems fuelled by solar energy (as in photosynthetic systems) or by the chemical energy stored in the molecular bonds of nucleotide triphosphates (for example, ATP).
- Biological motors convert chemical energy to effect stepwise linear or rotary motion, and are essential in controlling and performing a wide variety of biological functions. Linear motor proteins are central to many biological processes including muscle contraction, intracellular transport and signal transduction, and ATP synthase, a genuine molecular rotary motor, is involved in the synthesis and hydrolysis of ATP. Other fascinating examples include membrane translocation proteins, the flagella motor that enables bacterial movement and proteins that can entrap and release guests through chemomechanical motion.
- Whereas nature is capable of maintaining and repairing damaged molecular systems, such complex repair mechanisms are beyond the capabilities of current nanotechnology.
- In designing motors at the molecular level, random thermal brownian motion must therefore be taken into consideration. Indeed, nature uses the concept of the brownian ratchet to excellent effect in the action of linear and rotary protein motors. In contrast to ordinary motors, in which energy input induces motion, biological motors use energy to restrain brownian motion selectively. In a brownian ratchet system the random-molecular-level motion is harnessed to achieve net directional movement, and crucially the resulting biased change in the system is not reversed but progresses in a linear or rotary fashion.
- Biosystems frequently rely on ATP as their energy source, however very few examples of artificial motors that use exothermic chemical reactions to power unidirectional rotary motion have been reported to date.
- That biological motors perform work and are engaged in well-defined mechanical tasks such as muscle contraction or the transport of objects is apparent in all living systems.
It is clear that the biological machines are inspiring the human drive toward exploiting the possibilities of mimicking, if not duplicating, what already exists in nature. They say in conclusion,
The exquisite solutions nature has found to control molecular motion, evident in the fascinating biological linear and rotary motors, has served as a major source of inspiration for scientists to conceptualize, design and build – using a bottom-up approach – entirely synthetic molecular machines. The desire, ultimately, to construct and control molecular machines, fuels one of the great endeavours of contemporary science….
….As complexity increases in these dynamic nanosystems, mastery of structure, function and communication across the traditional scientific boundaries will prove essential and indeed will serve to stimulate many areas of the synthetic, analytical and physical sciences. In view of the wide range of functions that biological motors play in nature and the role that macroscopic motors and machines play in daily life, the current limitation to the development and application of synthetic molecular machines and motors is perhaps only the imagination of the nanomotorists themselves.
These superlatives call for an explanation: how did nature achieve this level of technology, a level our best scientists can only view with awe as they attempt to catch up, using their brightest intelligence applied to design? Here is the simplistic, hand-waving explanation. In what should have been a paper permeated with unadulterated intelligent design, both human and biological, they slipped into the old Darwinian bad habit. Get ready with your baloney breathalyzer.
Understanding and harnessing such phenomenal biological systems provides a strong incentive to design active nanostructures that can operate as molecular machines, and although our current efforts to control motion at the molecular level may appear awkward compared with these natural systems, it should not be forgotten that nature has had a 4.5 billion year head start.
This is bad breath caused by Dar-wine. No matter the object under consideration, from a nanoscopic rotary motor with near perfect efficiency to a narwhal’s antenna or a butterfly’s photonic crystals, Darwin-drunk researchers continue to ascribe these wonders to blind, aimless, materialistic processes. If nature’s advantage were merely a head start, then Nature Nanotechnology would do better to tell its researchers to close their labs, put on blindfolds, and wander aimlessly about, bumping into each other, till something interesting happens.
As we wag our heads at the inebriation of scientists believing such things, let’s not forget what they said about biological machines. Those machines really do exist. They’re keeping you functioning. They’re enabling your brain to think. So think. Don’t try to drink and think, lest your breath stink and your common sense shrink.