Notes on Thermodynamics of Biomolecules

Burning wood and digesting food are essentially the same chemical reaction: the oxidation of carbon-containing biomolecules.
Firewood is mostly cellulose (a complex carbohydrate), while marshmallows contain sugars and other biomolecules.
These molecules contain reduced carbon bonds.
Oxidation of these bonds is thermodynamically favorable, releasing a large amount of energy.
Burning releases energy as heat and light.
Cells capture this energy to do useful work.

Thermodynamically favorable reactions don't always occur at a perceptible rate due to activation energy.
Analogy: Water in a jar has potential energy but won't flow out until a barrier (the jar) is overcome.
A siphon requires initial energy to pull water up, but then the water flows freely.
Fire needs a spark/lightning/friction to start; once going, the combustion of cellulose releases energy to ignite more wood.

Living things use enzymes to lower activation energy (catalysts).
Analogy: Enzymes are like a spout in the jar, reducing the barrier for reaction.
Enzymes can be regulated to control the rate of reaction (like a valve on the spout).
We can digest marshmallows (sugars) but not wood (cellulose) because we lack the necessary enzymes to break down cellulose.

Proteins, carbohydrates, fats, and nucleic acids can be broken down into constituent parts.
Cells can construct necessary complex biomolecules from these basic building blocks.
Proteins, regardless of the source (plant or animal), are broken down into amino acids.

Basic building blocks form complex biomolecules, which are organized into cells.
Cells are organized into tissues, and tissues into organisms.

Thermodynamics of chemical reactions relates directly to complex biological processes.