A virus efficiently packs its DNA into its capsule with a powerful molecular motor working against repulsive forces.
Many biologists do not consider viruses to be “alive” since they require a host to replicate their DNA. But what are we to make of a packing motor so good, nanotechnologists want to copy it?
The picture in a press release from UC San Diego is stunning. It looks like a spaceship on a stand. At the bottom of that capsule, though, is a motor that packs DNA into the capsule with amazing efficiency. The powerful motor has to work against atomic repulsive forces as the DNA strands start to repel each other in close packing. Occasionally, the motor pauses, as if to allow the strands to fall into place.
DNA is a long, unwieldy molecule that tends to repel itself because it is negatively charged, yet it can spool tightly. Within the heads of viruses, DNA can be packed to near crystalline densities, crammed in by a molecular motor.
“These are among the most powerful molecular motors we know of,” says Douglas Smith, a professor of physics whose group studies them.
Within an infected cell, it only takes minutes for a virus to replicate itself. Once inside the capsule (called a head or capsid) the DNA takes about 10 minutes to relax into position, even though there is practically no wiggle room. “How fast this virus packages DNA is determined by physics more than chemistry,” says Douglas Smith, a UC physics professor. Like an automatic hose reel, the motor is able to pack it in such a way that the DNA does not kink or tangle.
“We tend to think of DNA for its information content, but living systems must also accommodate the physical properties of such a long molecule,” Berndsen said. “Viruses and cells have to deal with the forces involved.”
Yet the DNA contains the information to construct this motor inside the host cell. It’s both informational and mechanical.
Why study virus motors? One obvious motivation is to understand them for health reasons. Another reason, though, is to imitate them:
Beyond a clearer understanding of how viruses operate, the approach offers a natural system that is a model for understanding and studying the physics of long polymers like DNA in confined spaces. The insights could also inform biotechnologies that enclose long polymers within minuscule channels and spheres in nanscale devices.
Studying biological motors is of great interest for nanotechnology, a huge emerging field in engineering. An article in Nanotechnology Now says that nanoengineers want to learn from biology how to make tiny things move:
Nano– and micromotors are ultra-small devices designed to perform selected mechanical movements in response to specific stimuli. These movements include rotation, rolling, shuttling, delivery, contraction or collective behaviour, depending on the design of the motor and its biologically or chemically functionalized components.
PhysOrg’s copy of the article includes a short video clip of nanomotors at work. “Nano– and micromotors are often mimics of natural biological motors,” the article says. Nanomotors “offer extraordinary potential for future biochemical and biomedical applications,” the article says. Given the source of inspiration, it may be difficult in the future to tell the biological from the artificial.
Are viruses designed? Those motors sure look designed. That’s all intelligent design theory (ID) can decide: designed or not designed? Using certain criteria, ID can determine if an object shows sufficient evidence of an intelligent cause, instead of an unguided cause like natural selection It cannot identify the intelligence. It cannot say whether the cause is good or evil. Addressing those questions requires more information, such as that found in the Bible. Genesis teaches that suffering and death had its origin in the Fall (Genesis 3). That information, while foundational, is not exhaustive: nothing is said about viruses.
Reasoning from the nature of God and the evidence of this motor’s design, we might conclude that viruses originally had a good function. Many of them, in fact, still do today; only a small fraction cause disease. We don’t have enough information to know whether God changed some viruses as part of the curse, or allowed Satan to manipulate them for evil, or if some viruses mutated naturally and started wreaking havoc like a robot going berserk in a factory. What seems clear, though, combining ID and theology, is that viruses show complex design that defies evolution, and must have been originally designed for good. With those inferences, we can respect their design while trying to control the ill effects of those that cause us harm.