EnergyEnergy is the capacity to do work, or thecapacity for change.Energy transformations are linked tochemical transformations (reactions) incells.
Types of EnergyPotential energy: is stored energy - chemical bonds - concentration gradient - charge imbalance, etc.Kinetic energy: is the energy of movement
BiochemistryMetabolism: Sum total of all chemical reactionsin an organism.Anabolic reactions: Complex molecules aremade from simple molecules; energy input isrequired.Catabolic reactions: Complex molecules arebroken down to simpler ones and energy isreleased.
Laws of ThermodynamicsThermo - “energy”Dynamics - “change”Apply to all matter and all energytransformations in the universe.
First Law of ThermodynamicsEnergy is neither created nor destroyed.When energy is converted from one formto another, the total energy before andafter the conversion is the same.
Second Law of ThermodynamicsWhen energy is converted from one form toanother, some of that energy becomesunavailable to do work.No energy transformation is 100% efficient.
How is Energy Related…In any system: Total energy = usable energy + unusable energy enthalpy (H) = free energy (G) + entropy (S)H = G + TS (T = absolute temperature)G = H – TSEntropy is a measure of the disorder in a system.
Energy to do WorkChange in free energy (ΔG) in a reaction isthe difference in free energy of theproducts and the reactants.ΔG = ΔH – TΔS•If ΔG is negative, free energy is released•If ΔG is positive, free energy is consumed•At chemical equilibrium, ΔG = 0
BiochemistryExergonic reactions release free energy (–ΔG): Catabolism; complexity decreases (generates disorder).Endergonic reactions consume free energy (+ΔG): anabolism; complexity (order) increases.
ATPATP (adenosine triphosphate) capturesand transfers free energy.ATP releases a large amount of energywhen hydrolyzed.ATP can phosphorylate, or donatephosphate groups to other molecules.
ATPHydrolysis of ATPyields free energy.ΔG = –7.3 to –14kcal/mol (exergonic)
CatalystsSpeed up the rate of a reaction.The catalyst is not altered by thereactions.Most biological catalysts are enzymes(proteins) that act as a framework inwhich reactions can take place.
EnzymesHighly specificReactants are called substratesSubstrate molecules bind to the activesite of the enzymeThe three-dimensional shape of theenzyme determines the specificity
EnzymesThe enzyme-substrate complex (ES) is held together byhydrogen bonds, electrical attraction, or covalent bonds. E + S → ES → E + PThe enzyme may change when bound to the substrate, butreturns to its original form.
Enzymes Lower the Energy Barrier for ReactionsActivation Energy:The amount of energyneeded to initiate areactionAll reactions requireactivation energy.Exergonic vs.Endergonic Reactions
Enzyme PartnersProsthetic groups:(Permanent) Non-amino acid groupsbound to enzymesCofactors:(Reversible) InorganicionsCoenzymes:(Reversible) Smallcarbon-containingmolecules
The rate of a catalyzed reactiondepends on substrate concentrationConcentration of anenzyme is usuallymuch lower thanconcentration of asubstrate.At saturation, allenzyme is bound tosubstrate
Enzyme RegulationInhibitors: 2 Groups of Inhibitors:Molecules that bind to - Reversiblethe enzyme and slow - Irreversiblereaction rates. Irreversible inhibition:Naturally occurring Inhibitor covalently bonds to side chainsinhibitors regulate in the active site andmetabolism. permanently inactivates the enzyme.
Naturally Occurring InhibitorsReversible inhibition: Inhibitor bondsnoncovalently to the active site and preventssubstrate from binding.2 Types:– Competitive Inhibitors– Noncompetitive Inhibitors
Competitive InhibitorsCompete with thenatural substrate forbinding sites.When concentration ofcompetitive inhibitoris reduced, it detachesfrom the active site.
Noncompetitive InhibitorsBind to the enzyme ata different site (not theactive site).The enzyme changesshape and alters theactive site.
Metabolic PathwaysMetabolism is the thousands ofchemical reactions occurring incells simultaneouslyThese reactions are organized inmetabolic pathways.Each reaction is catalyzed by aspecific enzyme.The pathways are interconnected.Regulation of enzymes and thusreaction rates helps maintaininternal homeostasis.
Metabolic PathwaysThe first reaction is thecommitment step—otherreactions then happen insequence.Feedback inhibition (end-product inhibition): Thefinal product acts as anoncompetitive inhibitorof the first enzyme, whichshuts down the pathway.