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).
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