An Organism’s Metabolism Transforms Matter and Energy, Subject to the Laws of Thermodynamics

Kinetic and Potential Energy: Cheetah at Rest and Running

Energy is lost as heat

Kinetic and Potential Energy: Dam

 First Law of Thermodynamics: Energy Can Neither Be Created or Destroyed

Second Law of Thermodynamics: Every Energy Transfer Increases the Disorder (Entropy) of the Universe.

The Free Energy Change of a Reaction Tells Us Whether the Reaction Occurs Spontaneously

∆G = G Final State – G Initial State

The Relationship of Free Energy to Stability, Work Capacity, and

Spontaneous Change

Energy Changes in Exergonic (energy releasing) and Endergonic

(energy storing) Reactions

Disequilibrium and Work in Closed and Open Systems

• Cells in our body experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium

Figure 8.7

(b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equilibrium.

∆G < 0

• ATP powers cellular work by coupling exergonic reactions to endergonic reactions

• A cell does three main kinds of work:– Mechanical– Transport– Chemical

• The three types of cellular workare powered by the hydrolysis of ATP

(c) Chemical work: ATP phosphorylates key reactants

P

Membraneprotein

Motor protein

P i

Protein moved(a) Mechanical work: ATP phosphorylates motor proteins

ATP

(b) Transport work: ATP phosphorylates transport proteins

Solute

P P i

transportedSolute

GluGlu

NH3

NH2

P i

P i

+ +

Reactants: Glutamic acid and ammonia

Product (glutamine)made

ADP+

P

Figure 8.11

The Structure and Hydrolysis of ATP

 Energy Coupling by Phosphate Transfer

The Regeneration of ATP• Catabolic pathways drive the

regeneration of ATP from ADP and phosphate

ATP synthesis from ADP + P i requires energy

ATP

ADP + P i

Energy for cellular work(endergonic, energy-consuming processes)

Energy from catabolism(exergonic, energy yieldingprocesses)

ATP hydrolysis to ADP + P i yields energy

Figure 8.12

Example of an Enzyme-Catalyzed Reaction: Hydrolysis of Sucrose

•

Enzymes speed up metabolic reactions by lowering energy barriers

EnzymesEnzymes

1.1.ProteinsProteins:: most enzymesenzymes are catalytic proteinsproteins, primarily tertiarytertiary and quaternary quaternary structures.structures.

2.2.CatalystsCatalysts::chemical agentschemical agents that accelerateaccelerate a reaction without being permanently changed in the process.

How Do Reactions Occur?• Spontaneous reactions may

occur very slowly.• All reactions require free energy

of activation (EA)

• Uphill portion represents the EA

required to start the reaction.• Downhill portion represents the

loss of free energy by the molecules in the reaction.

Is this reaction exergonic or endergonic?

How can the EA barrier be overcome?

• Temperature• Temperatures that are too high

denature organic molecules, so what else is there?

• Enzymes lower the EA barrier so that reactions can occur at lower temperatures.

EnzymesEnzymes

FreeEnergy

Progress of the reaction

Reactants

Products

Free energy of activationFree energy of activation

Without Enzyme

With Enzyme

Enzyme / Substrate Relationship:

• What is the substrate?

• It is the reactant upon which an enzyme reacts.

• Enzymes are substrate specific.

• Only the active site of the enzyme actually binds the substrate.

SubstrateSubstrate

• The substancesubstance (reactant) an enzymeenzyme acts on.

Enzyme

Substrate

Active SiteActive Site

• A restricted regionrestricted region of an enzymeenzyme molecule which bindsbinds to the substratesubstrate.

Enzyme

Active Site

Substrate

The Active Site• Most enzyme-substrate

interactions are the result of weak bonds.

• The active site may cause the enzyme to hold onto the substrate in a very specific way.

• The active site may provide a micro-environment (e.g. low pH) which enhances a reaction.

Induced FitInduced Fit• A changechange in the configurationconfiguration of an

enzyme’senzyme’s active siteactive site (H and ionic bonds are involved).

• InducedInduced by the substratesubstrate..

Enzyme

Active Sitesubstrate

induced fit

Enzymatic ReactionEnzymatic Reactionsubstrate (sucrose)substrate (sucrose) + enzyme (sucrase) enzyme (sucrase)

enzymeenzyme--substratesubstrate complex complex

and +sucrasesucrase

glucoseglucose fructosefructose

productsproducts + + enzymeenzyme

Enzyme Activity is Affected by:• Temperature• pH• Enzyme Concentration• Substrate Concentration

Cofactors and CoenzymesCofactors and Coenzymes

• Inorganic substances (zinc, iron) Inorganic substances (zinc, iron) and vitamins vitamins (respectively) are sometimes needed for proper enzymatic activityenzymatic activity.

• ExampleExample::

IronIron must be present in the quaternary structurequaternary structure -- hemoglobinhemoglobin in order for it to pick up oxygen.

Enzyme InhibitorsEnzyme Inhibitors• Two examples:Two examples:

a.a. Competitive InhibitorsCompetitive Inhibitors:: are chemicals that resembleresemble an enzyme’s normal substrateenzyme’s normal substrate and competecompete with it for the active siteactive site.

Enzyme

Competitive inhibitor

Substrate

Enzyme InhibitorsEnzyme Inhibitorsb.b. Noncompetitive InhibitorsNoncompetitive Inhibitors::

Inhibitors that do not enter the do not enter the active siteactive site, but bind to another bind to another partpart of the enzymeenzyme causing the enzymeenzyme to change its shapechange its shape, which in turn alters the active sitealters the active site.

SubstrateEnzyme

active site altered

NoncompetitiveInhibitor

Allosteric Regulation• Regulatory molecules that bind to

the enzyme’s allosteric site changing the shape of the enzyme.

• Allosterically regulated enzymes have a quaternary protein structure.

• Each subunit of the enzyme has an active site and an allosteric site.

• Allosteric activators stabilize the active site

• Allosteric inhibitors deactivate the active site.

Feedback Inhibition

1) In the amylase lab, the amylase broke down the polysac-charides (starches) into _______.

2) Enzymes work by lowering the ___________ _________ required for a reaction to occur.