The Second Law and Life

In this weeks blog, I will describe the second law of thermodynamics and how it applies to biochemical mechanisms. There seems to be a lot of confusion, misunderstanding, and downright misrepresentation of this topic, so the intent here is to clarify everything.

The second law of thermodynamics states that the entropy always increases for spontaneous processes. Notice here that the reference frame is not specified. This is because, in most scientific realms, the context is assumed to either be an isolated system or the universe as a whole. Also notice that I said entropy always increases for a spontaneous process. For non-spontaneous processes, the entropy decreases. I will talk about spontaneous thermodynamic processes in this blog. Later today, I will post a an entry in my other blog talking about non-spontaneous thermal processes.

The Second Law of Thermodynamics tells us whether a process is spontaneous or not. This is based on the heat flow of the system (also known as enthalpy), the disorder of the system and its surroundings (referred to as entropy), and the temperature of a system. If a system is spontaneous, then the entropy of the entire universe goes up. This law basically states that, for a spontaneously occurring event (an event that has no intervention from a sentient being), the change in entropy of the system (the thing we are looking at) and the change in entropy of the surroundings (everything in the general vicinity of what we're looking at), when added together, gives us a positive number which is not zero. This means that the entropy of a system can go down can go down even as the total entropy of the universe goes up, provided that the two phenomena are causally related (one causes the other).

The equation for this, in case you're deathly curious, looks like ΔS(system)+ΔS(surroundings)>0. (As a side note here, the Greek capital letter delta is used in science to denote a change in a quantity.)  This holds true for isolated systems (system where no stuff is coming in or going out of it), because at this point, the change in entropy of the surroundings is zero, which means that the entropy of the system has to be positive. But alas, we have nothing which is truly isolated. The closest nature has gotten to a truly isolated system is a black hole, but that isn't truly isolated because stuff still goes into it. So for everything in our realm of existence, the change in entropy in the surroundings is never zero. Neither is the change in entropy in the system.

This is the heart of the Second Law of Thermodynamics.

For the formation of DNA, there is a drop in entropy of the system (the molecules of which make up DNA), but there is a release of heat associated with this formation. Even a rudimentary study of heat should tell you that the more heat something has, the more entropy it has. You put heat from the stove top into a pot of water for pasta, and the water goes chaotic as it boils. This is the nature of entropy. The magnitude of heat released by the formation of the double helix of DNA gives an increase of entropy to the surroundings which is greater then the drop of entropy of the DNA itself. Therefor, the total entropy of the universe goes up. The increase in total entropy tells us that for that this particular formation obeys the Second Law. So yes, it can for in nature.

In case you're interested, the particular equation used for the Second Law is ΔG=ΔH-T ΔS, where the G is Gibbs Free Energy (the measure of energy we can use from a thermal process), H is enthalpy, T is temperature, and S is entropy. It is derived from observation of the change in energy of the system, the transfer of heat, the temperature it is done at, and the order of everything in and near the system. Meticulous experiments have been done on this topic, and the observations of these experiments correspond to consistency with the Second Law of Thermodynamics.

What does this mean for life on Earth? If the energy being released from the creation of the basic building blocks of life is greater then the lowering of entropy, then there is an increase in the total entropy of the universe, and the Second Law of Thermodynamics is not broken.  This means that the creation of the basic building blocks of life at very least can be assembled spontaneously.  This proof of concept has been done in the lab on numerous occasions.

My prompt for you today is more intricately related to the post then usual. Todays prompt for you is to research the direct experimental papers for the change of temperature related to the formation of the basic building blocks of life. Do not use wikipedia, nor any public news sources. These sources are not the best for actual raw data collection. Go to google and type the terms you think will get you to the raw data which biochemists have obtained experimentally, and collect that data. Then run the numbers in the equation above. If the calculations you get turn up a negative value for ΔG, then the Second Law is not broken.

Until next week, have fun. Learn. And don't forget to be awesome.

-K. “Alan” Eister Δαβ

References:

The following concepts come from the General Chemistry text book Chemistry: The Central Science; by Theodore L. Brown, H. Eugene LeMay, Jr., Bruce E. Bursten, and Catherine J. Murphy:

Enthalpy (page s 175 and 177), entropy (page 806), Gibbs Free Energy (page 819), equation for spontaneity (page 819), and an isolated system (page 168).