There’s energy and then there’s "Energy," I guess. There is no additional external energy required for the binding of a virus to its receptor. It’s a spontaneous process in the thermodynamic sense. You could argue that the virus acquired energy from its prior host, but the virion itself carries nothing with it that generates or manipulates energy the way a cell or mitochondria does.

What sort of simple machine do you envision? The assembly of virions does require energy. That’s why viruses have to use a host to replicate; viruses lack metabolic/energetic machinery so they usurp their host’s. But this is not the same energetic question as binding to a receptor.

the mechanism of the binding is a spontaneous process so probably the binding uses the heat of the environment. Perhaps you could run an experiment and see if the virus binds in cold temperatures?

The virus functions much like any other receptor-binding molecule: it takes advantage of molecular forces, such a van der Vaal’s interactions, hydrophobic interactions, hydrogen bonding etc. So, the initial recognition of the target uses some of those forces (possibly other similar forces as well). However, the entry to the cells is often phagocytotic, or with enveloped viruses, fusion of the lipid membranes. These mechanisms use the host cell’s energy sources – the virus kind of "fools" the host cell to think it is a useful particle or something, and the cell (again) does the work for the virus. And from there, all the energy required is stolen from the unfortunate host cell 🙂

EDIT: Oh, and what comes to the ability of viruses to bind their target in cold – I think the same rules apply than with many other molecular reactions, they get slower when it gets colder – naturyally when water freezes the activity pretty much stops. So I think viruses are capable of binding in cold, but far less efficiently. That in turn means, that the energy required in viral functions ultimately comes from thermodynamics. No heat = no energy, or so.

I think it is useful to contemplate the impossible. Every once in a while the impossible turns out not to be so impossible after all. Perhaps someday there will be a physics beyond “mere” thermodynamics, but so far there is no known process that violates the rule that it is impossible to create a heat engine with 100% efficiency, which is what you would have to do to create a car that runs without fuel. Doesn’t matter if you’re talking about mechanical systems or heat engines, the principles are the same. There is also the problem of mechanically connecting forces measured in the range of pN on the microscopic level of the individual molecule, to forces required to, say, throw a baseball. Tropomyosin/actin molecules in muscle do this all the time, of course, but this process requires ATP.

You may be interested in looking at things like DNA and/or quantum computers—which compute efficiently, but don’t in themselves move macroscopic objects around in space. A DNA computer has already been built (not that HP or Dell plans on selling one anytime soon), and they are working on prototype quantum dot computers. You might also be interested to read some papers on how people measure the properties of individual molecules of DNA or proteins. It’s not so straightforward and it’s taken over a decade to be able to do it reliably, but it can be done.

I just read an article on the thermodynamics of cellular systems (can’t remember where) – at the moment, the mechanisms of classic thermodynamics can’t be translated to cells, so at the moment we can’t be completely sure that big machines are analogous to little biological ones.

Darby if you recall that article, please post it. This is a topic I have been pondering for quite sometime.

BTW, if thermodynamics cant be applied to the cell…..GOD anyone?

GOD or insufficient knowledge. Take your pick

Obviously they’re not saying themodynamics can’t be applied to the cell, but rather a classical approach would neglect quantum effects.