Thermodynamics and Metabolism

Thermodynamics: the science of energy transformations (flow of energy through living and non- living systems)

All living things require ENERGY – which is the capacity for doing work Forms of energy: thermal light chemical electrical

KINETIC ENERGY Energy of motion: – Falling water – Pistons in a car engine – Skier going down a hill – Examples on a molecular scale include the energy of vibrations, random diffusion, and heat.

POTENTIAL ENERGY stored energy Example: Molecules of glucose have potential energy, stored in bonds

FIRST LAW OF THERMODYNAMICS Energy can neither be created nor destroyed, but can be transformed from one form to another. eg: during photosynthesis, light energy from the Sun is transformed into chemical energy stored in the bonds of glucose

During cellular respiration, the energy in the bonds of glucose is released and is transformed into new molecules (ATP), motion, and heat energy.

Photosynthesis and Respiration Photosynthesis Respiration produces food stores energy uses water uses carbon dioxide releases oxygen occurs in sunlight uses food releases energy produces water produces carbon dioxide uses oxygen occurs in the dark as well as light

There is ALWAYS some loss of useful energy. The Second LAW OF THERMODYNAMICS: Every energy transformation increases the entropy of the universe.

The second law of thermodynamics In all processes or reactions, some of the energy involved irreversibly loses its ability to do work. or In any reaction the amount of molecular disorder always increases

Entropy is a measure of the randomness or disorder in a collection of objects Entropy increases… when solids become liquids or gases Complex molecules react to form simpler molecules (catabolic reactions) During diffusion

Living systems seem to break the second Law of Thermodynamics Anabolic processes in cells build highly ordered structures (e.g.; proteins and DNA) from a random assortment of molecules (amino acids and nucleotides) in the cell fluids.

On a large scale, living organisms build and maintain highly ordered structures such as cells, tissues, organs and systems, as well as nests, webs and homes. All of these changes cause the universe to become a little more ordered.

But these anabolic processes are coupled to catabolic processes Which release free energy and thermal energy and increase the entropy of the universe. Living organisms create order in a local part of the universe at the expense of greater a greater amount of disorder in the universe as a whole.

Free energy It is clear that we should be concerned only with energy available to do useful work, so-called free energy or Gibbs energy. Josiah Willard Gibbs ( )

Exothermic Reactions Produce energy (exergonic reactions) Tend to increase entropy (therefore, spontaneous) –- delta G value E.g.; cellular respiration

Exothermic Reaction

B) Endothermic Reactions Require energy (endergonic reactions) Tend to decrease entropy (because they create big/organized molecules) Are not spontaneous –+ delta G values E.g.; photosynthesis

The Transition state describes the temporary conditions in which the bonds within reactants are breaking and the bonds between products are forming.

Activation Energy (E A ) :amount of energy needed to strain and break the reactants' bonds in a biochemical reaction

For an exergonic reaction,  G is negative. For an endergonic reaction,  G is positive.

ATP ATP is the primary source of free energy in living cells.

ATP transports chemical energy within cells for metabolism. Metabolic processes that use ATP as an energy source convert it back into ADP and inorganic phosphate(P i ) precursors. ATP is therefore continuously recycled in organisms: the human body, contains 250 grams of ATP on average, and turns over its own weight in ATP each day.

Phosphorylation When ATP is used as an energy source, the energy is NOT released as heat. Instead, the hydrolysis of ATP is usually coupled to a reaction which attaches the phosphate group to another molecule directly associated with the work that needs to be done. (What example of this have you seen?) Attaching the phosphate group (phosphorylation) makes the other molecule more reactive

Redox reactions In living systems, free energy must be released in small quantities. The hydrolysis of ATP and the phosphorylation of molecules is one way to accomplish this, Another is coupled oxidation-reduction reactions.

The transfer of electrons ( and H+) from one substance to another is a way of transferring free energy. The electronegativity of each substance in the “chain” must be greater than the molecule that preceded it. Redox reactions are used to create ATP.