Chemical Reactions in Cells. Energetics, Enzymes and Metabolic Reactions. Energy. Energy is the capacity for work or change. Kinetic Energy = energy of movement Potential Energy = stored energy 1 st Law of Thermodynamics
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Energetics, Enzymes and Metabolic Reactions
reaction = Gproducts – Greactants
SFree Energy = Energy Useful for Change
Reactants changed to transition-state species
Progress of reactionExergonic Reactions
Burning glucose (sugar):an exergonic reaction
Activation energy neededto ignite glucose
Glucose + O2
Energy released byburning glucose
C O2 + H2O
Progress of reactionEndergonic Reactions
Photosynthesis:an endergonic reaction
Net energycaptured bysynthesizingglucose
Activationenergy fromlight capturedby photosynthesis
CO2 + H2O
D. Which type of reaction would have a positive value for G?Applying Your Knowledge
A. Which type of reaction would be spontaneous?
B. For which type of reaction will the products have a higher energy than the reactants?
C. Which type of reaction releases energy?
+ Pi+ free energyATP Provides Energy for Cellular Reactions
Pairing of an Exergonic reaction, often involving ATP, with an Endergonic reaction
Note that overall free energy change is negative
Enzymes are biological catalysts.
biological: composed of protein or, rarely, RNA
catalyst: speeds up a reaction without being changed by the reaction
–The value of and the ratio of reactants and products at equilibrium is the same as for an uncatalyzed reactionProperties of Enzymes
Progress of reactionActivation Energy: Controls Rate of Reaction
Amount of energy required for reaction to occur
1 Substrates enter active site
2 Shape change promotes reaction
Product released;enzyme ready again
Rate no longer increases since the active sites of all enzymes are saturated with substrate
Rate is more rapid
Rate is proportional to substrate concentration
Feedback InhibitionIsoleucine allosterically inhibits enzyme 1Enzyme Regulation: Feedback Inhibition
Feedback Inhibition: The product of a pathway inhibits an initial step in the pathway to decrease its own production
fewer collisions between enzyme and substrate
enzyme unfolds(denatures)Effects of Temperature and pH on Enzymatic Activity
Where do the substrates bind?
Enzymes (raise or lower) the (1, 2, 3, 4 or 5) of a reaction.
What is the model for a shape change caused by substrate binding to the enzyme?
Induced fitApplying Your Knowledge