Biology Lecture No. 5: Thermodynamics
Monday January 23rd, 2012
Energy & Thermodynamics:
-Thermodynamics is fundamental to biological functions in the body.
-Energy can be defined as the capacity to do work.
-Kinetic energy is the form of energy associated with motion.
-Gravitational Potential energy is the form of energy associated with position relative to the
-Chemical Potential energy is the form of energy associated with the structure of molecules.
Forms Of Systems:
-A system is defined as the area or space in which a reaction or process occurs. An example of a system
could be a molecule, a cell, or even the Earth.
-The surroundings is what encompasses everything outside the system in question.
-An Isolated System is one that does not exchange matter or energy with the surroundings.
-A Closed System is one that is only capable of exchanging energy with the surroundings.
-An Open System is one that may exchange both matter and energy.
The First Law Of Thermodynamics:
-The 1 Law of Thermodynamics states that the total energy in the universe is constant. It cannot be
created or destroyed; it may only be converted from one form to another.
-Niagara Falls is a system where the potential energy of the water is greatest at the top of the waterfall,
but at the bottom of the waterfall the kinetic energy of the water is at its maximum.
-A turbine is responsible for transforming gravitational potential energy into usable forms of energy,
such as hydro-electric power. However this transformation, like most known processes, is not 100%
efficient as some of the original energy is lost during the transformation process.
The Second Law Of Thermodynamics:
-The 2 Law of Thermodynamics states that transformation increases the spontaneity of the universe.
This spontaneity or randomness is known as entropy. -All known energy transformations are never 100% efficient, energy tends to always be lost or wasted in
order to increase the entropy of the universe. The spontaneity of an isolated system will always
Entropy & Protein Synthesis:
-One of the key physical objects known in biology is proteins.
-Proteins are macromolecules that are constantly breaking down or losing the efficacy of their intended
-Therefore, constant transcription and translation is necessary due to the inevitable increase in entropy.
- Around 90% of the proteins constantly undergoing transcription and translation are for the chloroplast
and mitochondria organelles.
Can Spontaneous Reactions Occur? :
-Spontaneous reactions are those which do not require a supply of energy to attain completion.
-Reactions tend to be spontaneous when products have a lower potential energy than the reactants.
-Total energy content of a system is known as its enthalpy (H).
-Energy that is exothermic is released in reaction (the products possess lower potential energy than the
reactants), while energy that is absorbed in reaction is endothermic (the products have greater enthalpy
than the reactants).
-Reactions also tend to be spontaneous when products are less ordered (denoting more entropy or
randomness) than the reactants. The entropy (S) therefore increases.
Gibb’s Free Energy (∆G):
-Gibb’s free energy describes the available energy present to do work that does not include energy
available from entropy. Free energy is calculated as ∆G = ∆H - T∆S.
-An exergonic reaction is one where the free energy of the reactants is greater than the free energy of
the products. All exergonic reactions are spontaneous. I