All metabolic processes or chemical reactions within cells
involves some sort of change in free energy.
We call this change in free energy ΔG.
ΔG is free energy that is available to do work.
And this looks like kind of a crazy equation
but really it's not that complex.
ΔH, we measure that as the energy stored in bonds.
So free energy equals all the energy stored in bonds,
let's say of a glucose molecule,
minus what we lost to disorder in the universe.
So temperature plays a factor in this,
but the key here really is not what the equation says
as much as it is understanding the concept of ΔG.
ΔG being the energy available to do work, right.
It's either positive or negative.
If we have a system in which the products are at lower energy
than reactants, for example photosynthesis,
we're putting energy into the system,
we have a positive ΔG, right.
We're adding energy to the system, the products now,
in this case glucose have much higher energy
than the carbon dioxides that went in, and that energy
is stored in the chemical bonds, those covalent bonds.
So energy has to be supplied, and in a system where energy
has to be supplied, we call this an endergonic reaction.
Endo meaning going inside, we're putting energy into the system,
so it's an endergonic reaction.
I mean the reactants are higher energy than the product,
so glucose has higher energy than the products that we release from it.
Carbon dioxide gets released make sense,
and so we have a negative ΔG.
In systems where we have energy being released,
we call them exergonic. Energy coming out like exercise.
So exergonic reactions in general, are spontaneous.
But there is a little bit of a catch.
Imagine if you are trying to set a log on fire. That log is probably
not going to spontaneously combust although theoretically it could.
You probably need to use a match to light it. If you were to
just wait for it to spontaneously combust, it might take a long time.
And this waiting for it to actually happen naturally
is the activation energy.
If we use a match, then we can spark the fire,
a little bit of energy is input,
but much more quickly we are able to overcome this energy hump,
right, or the activation energy,
in order to burn the log and release lots of heat from it, right.
So activation energy can be reduced in biological systems
through the use of enzymes.
Pretty much any of the reactions that we have,
if they are exergonic, would proceed spontaneously,
however it might take several hundred thousand years
and I don't have time to wait that long
for all of my endergonic processes to happen.
So thankfully we have enzymes to help in the process.