Chemical and Physical Foundations of Biological Systems Section: Content Category 5E

Principles of chemical thermodynamics and kinetics
The processes that occur in living systems are dynamic, and they follow the principles of chemical thermodynamics and kinetics. The position of chemical equilibrium is dictated by the relative energies of products and reactants. The rate at which chemical equilibrium is attained is dictated by a variety of factors: concentration of reactants, temperature, and the amount of catalyst (if any).

Biological systems have evolved to harness energy, and utilize it in very efficient ways to support all processes of life, including homeostasis and anabolism. Biological catalysts, known as enzymes, have evolved to allow all of the relevant chemical reactions required to sustain life to occur both rapidly and efficiently, and under the narrow set of conditions required.

The content in this category covers all principles of chemical thermodynamics and kinetics including enzymatic catalysis. The topics and subtopics are below:

Topic Level Key:

The abbreviations found in parentheses indicate the course(s) in which undergraduate students at many colleges and universities learn about the topics and associated subtopics. The course abbreviations are:

BC = first-semester biochemistry
BIO = two-semester sequence of introductory biology
GC = two-semester sequence of general chemistry
PHY = two-semester sequence of introductory physics

Please note topics that appear on multiple content lists will be treated differently. Questions will focus on the topics as they are described in the narrative for the content category.

Enzymes (BC)

  • Classification by reaction type
  • Mechanism
    • Substrates and enzyme specificity
    • Active site model
    • Induced-fit model
    • Cofactors, coenzymes, and vitamins
  • Kinetics
    • General (catalysis)
    • Michaelis–Menten
    • Cooperativity
    • Effects of local conditions on enzyme activity
  • Inhibition
  • Regulatory enzymes
    • Allosteric
    • Covalently modified

Principles of Bioenergetics (BC)

  • Bioenergetics/thermodynamics
    • Free energy/Keq
    • Concentration
  • Phosphorylation/ATP
    • ATP hydrolysis ΔG << 0
    • ATP group transfers
  • Biological oxidation–reduction
    • Half-reactions
    • Soluble electron carriers
    • Flavoproteins

Energy Changes in Chemical Reactions – Thermochemistry, Thermodynamics (GC, PHYC)

  • Thermodynamic system – state function
  • Zeroth Law – concept of temperature
  • First Law - conservation of energy in thermodynamic processes
  • PV diagram: work done = area under or enclosed by curve (PHY)
  • Second Law – concept of entropy
    • Entropy as a measure of “disorder”
    • Relative entropy for gas, liquid, and crystal states
  • Measurement of heat changes (calorimetry), heat capacity, specific heat
  • Heat transfer – conduction, convection, radiation (PHY)
  • Endothermic/exothermic reactions (GC)
    • Enthalpy, H, and standard heats of reaction and formation
    • Hess’ Law of Heat Summation
  • Bond dissociation energy as related to heats of formation (GC)
  • Free energy: G (GC)
  • Spontaneous reactions and ΔG° (GC)
  • Coefficient of expansion (PHY)
  • Heat of fusion, heat of vaporization
  • Phase diagram: pressure and temperature

Rate Processes in Chemical Reactions - Kinetics and Equilibrium (GC)

  • Reaction rate
  • Dependence of reaction rate on concentration of reactants
    • Rate law, rate constant
    • Reaction order
  • Rate-determining step
  • Dependence of reaction rate upon temperature
    • Activation energy
      • Activated complex or transition state
      • Interpretation of energy profiles showing energies of reactants, products, activation energy, and ΔH for the reaction
    • Use of the Arrhenius Equation
  • Kinetic control versus thermodynamic control of a reaction
  • Catalysts
  • Equilibrium in reversible chemical reactions
    • Law of Mass Action
    • Equilibrium Constant
    • Application of Le Châtelier’s Principle
  • Relationship of the equilibrium constant and ΔG°

To support your studies, see the following video tutorials below from the Khan Academy MCAT Collection. The videos and associated questions were created by the Khan Academy in collaboration with the AAMC and the Robert Wood Johnson Foundation.