Lecture 4: Energy and Enzymes
Independent Study Outcomes:
Isolated, closed and open systems.
• Isolated System: does not exchange matter or energy with its
surroundings. (e.g. thermos)
• Closed System: can exchange energy, but not matter, with its
surroundings. (e.g. earth- releases heat energy, but no matter)
• Open System: both energy and matter can move freely between the
system and the surroundings. (e.g. the ocean)
First law of thermodynamics
• First Law of Thermodynamics: energy can be transformed from one
form into another or transferred from one place to another, but it cannot be
created or destroyed. (Principle of the conservation of energy)
-Photosynthesis is a good example of first law, you can take photon
of light and convert it to chemical energy.
Second law of thermodynamics
• Second Law of Thermodynamics: the total disorder of a system and its
surrounding always increases.
o Systems will move spontaneously toward arrangements with
greater disorder—greater entropy
• Cells only able to convert 40% of potential energy in glucose into a form
useable for metabolism; heat is lost to environment
• Unusable energy produced during energy transformations results in an
increase in the disorder or randomness of the universe
• Entropy: randomness or disorder.
What is meant by the phrase "it takes energy to maintain low entropy"
• It takes energy to maintain low entropy
o i.e. need car mechanic to fix car when it starts breaking down
• living cells have ability to create ordered structures or of less ordered
• living cells are open systems
• living things bring in energy and matter and use them to generate order
out of disorder
o most of food we eat is to maintain our cells in their highly ordered
o cell components (proteins, organelles) become damaged and
constantly need repair or replacements
by synthesis of proteins, carbohydrates, lipid molecules
• living things give off heat and metabolic byproducts (CO2) that are much
les ordered, and increase the disorder/entropy of surroundings.
Lecture Outcomes: Photons from the sun (light), they represent low entropy energy, because
photosynthetic organisms can transform those photons from low entropy
and then produce low entropy energy (glucose, proteins, nucleic acids…)
meaning of potential, kinetic, chemical energy, closed,
open vs. isolated systems, First Law of
Thermodynamics, Second Law of Thermodynamics,
entropy, spontaneous reaction, enthalpy (H), DH,
exothermic, endothermic, Gibbs Free Energy,
exergonic, endergonic, DG, catalyst, rate of reaction, energy of activation
(EA), transition state, kinetic stability, active site, catalytic cycle
Why life does not go against the second law.
• 2 law of Thermodynamics- disorder of system+ surroundings increase
• cells are highly ordered, but….
o cells are open systems; exchange energy and matter with
o cells use energy to maintain order (low entropy)
>> entropy could be explained as energy spreading, dispersal.
Why life needs to consume energy
- You need huge amounts of calories because entropy causes things to break down,
so house keeping proteins have to be translated continually or the body will die.
• cells emit lots of heat; this increases disorder of surroundings
• huge amounts of energy in allows maintenance of low entropy
Components of Gibbs Free Energy equation
• It is the energy available to do work
• ∆G = ∆H -T∆S
• ∆ free energy= ∆ enthalpy (is it +endo/or –exothermic?)-
temperature( ∆ entropy “is it + more disorder/or – less disorder”)
Reactions tend to be spontaneous ((-ΔG)) means that it doesn’t need energy
to proceed “spontaneous /or do I need energy to do so?))
• enthalpy is potential energy
o could be biosynthetic pathway, or breakdown of molecule in the cell
o endothermic (+)
o exothermic (-)
• entropy is disorder
o more disorder (+)
o less disorder (-)
• free energy
o enerdergonic (+ G)
o exergonic (- G)
Whether or not a given reaction will be spontaneous, given DG • Reactions tend to be spontaneous (-∆G; exergonic) when… 2 things
o Reaction is exothermic ( energy is released, and entropy
increases e.g. glucose will spontaneously break down)
o Products are more disorder (entropy goes up)
Eg. 1: fermentation of glucose to ethanol
Melting of ice room temp. is spontaneous; driven by massive
change “increase” in entropy
gas and liquid are more disordered than a solid (entropy)
• some spontaneous reactions can take billions of years
Role of enzymes in endergonic vs. exergonic reactions
• Enzymes can increase rate of spontaneous reaction by 10 -10 20
• Why does life require enzymes?
o Without enzymes, the