AP BiologyAP Biology

Chapter 8Chapter 8Introduction to Introduction to

MetabolismMetabolism

MetabolismMetabolism The chemistry of life is organized into The chemistry of life is organized into

metabolic pathways.metabolic pathways. Metabolism Metabolism is the collection of is the collection of

chemical reactions that occur in an chemical reactions that occur in an organism. Most involve enzymes.organism. Most involve enzymes.

Catabolic pathwaysCatabolic pathways break down break down molecules to release energy.molecules to release energy.

Anabolic pathwaysAnabolic pathways build molecules build molecules and consume energy to do so.and consume energy to do so.

EnergyEnergy EnergyEnergy is the capacity to do work by is the capacity to do work by

moving matter.moving matter. Kinetic energyKinetic energy is energy of motion. is energy of motion. Potential energyPotential energy is stored in the is stored in the

location or structure of matter. This location or structure of matter. This includes chemical energy stored in includes chemical energy stored in chemical bonds.chemical bonds.

Energy can change form.Energy can change form.

Energy TransformationEnergy Transformation

Laws of ThermodynamicsLaws of Thermodynamics The study of the energy transformations The study of the energy transformations

that occur in a collection of matter is called that occur in a collection of matter is called thermodynamicsthermodynamics..

Organisms are Organisms are open systemsopen systems; energy can ; energy can be transferred between the system and its be transferred between the system and its surroundings.surroundings.

First Law of ThermodynamicsFirst Law of Thermodynamics: Energy : Energy can be transferred and transformed, but it can be transferred and transformed, but it can be neither created nor destroyed.can be neither created nor destroyed.

Second Law of ThermodynamicsSecond Law of Thermodynamics: Every : Every energy transfer or transformation increases energy transfer or transformation increases the the entropyentropy (disorder) of the universe. (disorder) of the universe.

Biological OrderBiological Order Biological order requires Biological order requires

energy to maintain its energy to maintain its complexity.complexity.

This does not violate the This does not violate the 22ndnd Law of Law of Thermodynamics.Thermodynamics.

In open systems, In open systems, organisms can increase organisms can increase their order at the their order at the expense of the order of expense of the order of their surroundings.their surroundings.

Matter can become Matter can become more ordered only if the more ordered only if the surroundings become surroundings become more disordered. more disordered.

Free EnergyFree Energy Organisms live at the expense of free Organisms live at the expense of free

energy.energy. A living system’s free energy is energy A living system’s free energy is energy

that can do work under cellular conditions.that can do work under cellular conditions. Free energy (Free energy (GG) is related directly to total ) is related directly to total

energy (energy (HH) and to entropy () and to entropy (SS).). In an In an exergonicexergonic (spontaneous) chemical (spontaneous) chemical

reaction, the products have less free reaction, the products have less free energy than the reactants.energy than the reactants.

EndergonicEndergonic (nonspontaneous) reactions (nonspontaneous) reactions require an input of energy.require an input of energy.

Free energy, cont.Free energy, cont.

In cellular metabolism, exergonic In cellular metabolism, exergonic reactions power endergonic reactions reactions power endergonic reactions (energy coupling).(energy coupling).

The addition of starting materials The addition of starting materials and the removal of end products and the removal of end products prevent metabolism from reaching prevent metabolism from reaching equilibrium.equilibrium.

ATPATP

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

Removing a phosphate group from Removing a phosphate group from ATP produces ADP and free energy.ATP produces ADP and free energy.

ATP, cont.ATP, cont. ATP drives endergonic reactions by transfer of the ATP drives endergonic reactions by transfer of the

phosphate to specific reactants, making them more phosphate to specific reactants, making them more reactive. Cells can carry out work, such as movement reactive. Cells can carry out work, such as movement or building molecules (anabolism).or building molecules (anabolism).

Catabolic pathways drive the regeneration of ATP from Catabolic pathways drive the regeneration of ATP from ADP and phosphate.ADP and phosphate.

EnzymesEnzymes

Enzymes speed up metabolic Enzymes speed up metabolic reactions by lowering energy reactions by lowering energy barriers.barriers.

Enzymes, which are proteins, are Enzymes, which are proteins, are biological catalysts. The speed up biological catalysts. The speed up reactions by lowering activation reactions by lowering activation energy (energy needed for reactions energy (energy needed for reactions to begin).to begin).

Enzymes, cont.Enzymes, cont.

Enzymes are substrate specific.Enzymes are substrate specific. Each type of enzyme has a unique Each type of enzyme has a unique

active site that combines specifically active site that combines specifically with its with its substratesubstrate, the reactant , the reactant molecule on which it acts.molecule on which it acts.

The enzyme changes shape slightly The enzyme changes shape slightly when it binds the substrate (induced when it binds the substrate (induced fit).fit).

How Enzymes WorkHow Enzymes Work

The The active siteactive site is an enzyme’s catalytic is an enzyme’s catalytic center.center.

The active site can lower activation energy The active site can lower activation energy by orienting substrates correctly, providing by orienting substrates correctly, providing a microenvironment that favors the a microenvironment that favors the reaction.reaction.

The enzyme forms an The enzyme forms an enzyme/substrate enzyme/substrate complexcomplex, but is not used up in the , but is not used up in the reaction; it is released to be used again.reaction; it is released to be used again.

Enzymes: Optimum Enzymes: Optimum conditionsconditions

As proteins, enzymes are sensitive to As proteins, enzymes are sensitive to conditions that influence their 3-D conditions that influence their 3-D structure.structure.

Each has an optimal temperature Each has an optimal temperature and pH. Outside of these favorable and pH. Outside of these favorable ranges, the protein can change ranges, the protein can change shape (denature) and no longer shape (denature) and no longer function effectively, if at all.function effectively, if at all.

Cofactors and CoenzymesCofactors and Coenzymes

Many enzymes require nonprotein Many enzymes require nonprotein helpers in order to be active. These helpers in order to be active. These are are cofactorscofactors..

Cofactors of some enzymes are Cofactors of some enzymes are inorganic, such as metal ions (Zn, Cu, inorganic, such as metal ions (Zn, Cu, or Fe).or Fe).

Cofactors that are organic molecules Cofactors that are organic molecules (such as vitamins) are called (such as vitamins) are called coenzymescoenzymes..

Enzyme InhibitorsEnzyme Inhibitors Certain chemicals can inhibit the Certain chemicals can inhibit the

activity of specific enzymes.activity of specific enzymes. Some inhibitors resemble the normal Some inhibitors resemble the normal

substrate and compete for the active substrate and compete for the active site. These are site. These are competitive competitive inhibitorsinhibitors, and reduce enzyme activity , and reduce enzyme activity by blocking the substrate from entering by blocking the substrate from entering the active site.the active site.

Noncompetitive inhibitorsNoncompetitive inhibitors prevent prevent enzymatic reactions by binding to enzymatic reactions by binding to another part of the enzyme, which another part of the enzyme, which causes the enzyme to change shape.causes the enzyme to change shape.

Control of Metabolism:Control of Metabolism:Allosteric regulationAllosteric regulation

Regulatory molecules change an enzyme’s Regulatory molecules change an enzyme’s shape and function by binding to an allosteric shape and function by binding to an allosteric site, a location different from the active site.site, a location different from the active site.

Some molecules are activators, which Some molecules are activators, which stabilizes the active site and stimulates stabilizes the active site and stimulates enzyme activity.enzyme activity.

Allosteric inhibitors stabilizes the inactive Allosteric inhibitors stabilizes the inactive form of the enzyme.form of the enzyme.

The molecules are weakly bonded to the The molecules are weakly bonded to the enzyme, and are basically reversible enzyme, and are basically reversible noncompetitive inhibitors.noncompetitive inhibitors.

Allosteric RegulatorsAllosteric Regulators

Feedback InhibitionFeedback Inhibition

Feedback inhibitionFeedback inhibition is the switching is the switching off of a metabolic pathway by its end-off of a metabolic pathway by its end-product.product.

The product acts as an inhibitor of an The product acts as an inhibitor of an enzyme within the pathway.enzyme within the pathway.

Feedback inhibition prevents the cell Feedback inhibition prevents the cell from wasting chemical resources to from wasting chemical resources to synthesize more product than is synthesize more product than is needed.needed.

CooperativityCooperativity CooperativityCooperativity is a mechanism that amplifies is a mechanism that amplifies

the response of enzymes to substrates.the response of enzymes to substrates. A substrate molecule binding to one active A substrate molecule binding to one active

site of a multi-subunit enzyme activates the site of a multi-subunit enzyme activates the other subunits.other subunits.

Localization of EnzymesLocalization of Enzymes

Localization of enzymes within a cell helps Localization of enzymes within a cell helps order metabolism.order metabolism.

Some enzymes are grouped into Some enzymes are grouped into complexes, some are incorporated into complexes, some are incorporated into membranes, and others are contained membranes, and others are contained inside organelles.inside organelles.

For example, mitochondria are membrane-For example, mitochondria are membrane-bound organelles in eukaryotic cells that bound organelles in eukaryotic cells that have a series enzymes working to carry have a series enzymes working to carry out cell respiration.out cell respiration.