BIO SCI 98 Lecture Notes - Lecture 6: Isoleucine, Reaction Coordinate, Enzyme Inhibitor
14 Jul 2018
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• Pg. 28-29 :
o Enzymes Promote Sequences of Chemical Reactions
• All biological macromolecules are much less thermodynamically stable than their
monomeric subunits yet that are kinetically stable (their uncatalyzed breakdown
occurs SO SLOWLY - over years rather than seconds - on a time scale that matters for
the organisms
• Enzymes: biocatalysts (proteins) that greatly enhance the rate of a specific chemical
reaction (by lowering activation energy) without being consumed in the process
• Activation barrier: path from reactants to products with energy barrier that must be
surmounted by any reaction to proceed
• Transition state: breaking of existing bonds and formation of new ones generally
requires distortion of existing bonds
• Activation energy (∆G'): highest point in the reaction coordinate diagram represents
the transition state and the difference n energy between the reactant in its ground
state and in its transition state
• Pathways: enzyme catalyzed chemical reactions are functionally organized into many
sequences of consecutive reactions in which the product of one reaction becomes the
reactant in the next
▪ Catabolism: output of energy
▪ Anabolism: require input of energy
o Metabolism is Regulated to Achieve Balance and Economy
• Living cells simultaneously synthesize thousands of different kinds of carbs, fats,
proteins, nucleic acids in precise propositions
▪ Ex. E. coli has 5 steps in the pathway
• IF a cell begins to product more isoleucine than needed for protein synthesis, the
unused isoleucine accumulates and the increased concentration inhibits the catalytic
activities of the first enzyme in the pathway, immediately slowing the production of
isoleucine
▪ This is known feedback inhibition which keeps the production and utilization of
each metabolic intermedia in balance
o SUMMARY:
• Living cells are OPEN SYSTEMS: exchanging matter and energy w/ their surroundings,
extracting/channeling energy to maintain themselves in a dynamic steady state
distant from equilibrium
▪ Energy is obtained from sunlight or fuels by converting the energy from electron
flow into the chemical bonds of ATP
• The tendency for a chemical reaction to proceed toward equilibrium is expressed as free
energy change (∆G) which ahs two components
▪ Enthalpy change ∆H (HEAT)
▪ Entropy change ∆S (DISORDER)
