Ground Rules of Ground Rules of MetabolismMetabolism

Chapter 6Chapter 6

Free RadicalsFree Radicals

Unbound molecular fragments with Unbound molecular fragments with

the wrong number of electrons the wrong number of electrons Highly reactiveHighly reactive Can disrupt structure of moleculesCan disrupt structure of molecules

Keeping Free Radicals Keeping Free Radicals in Checkin Check

superoxide dismutase catalase

Figure 6.1Page 96

Superoxide DismutaseSuperoxide Dismutase

Catalyzes the formation of Catalyzes the formation of hydrogen peroxide from oxygen-hydrogen peroxide from oxygen-free radicals and hydrogen ionsfree radicals and hydrogen ions

Accumulation of hydrogen Accumulation of hydrogen peroxide can be lethal to cellsperoxide can be lethal to cells

CatalaseCatalase

Catalyzes the formation of oxygen Catalyzes the formation of oxygen and water from hydrogen peroxideand water from hydrogen peroxide

2H2H22OO22 ----------> 2H ----------> 2H22O + OO + O22

What Is Energy?What Is Energy?

Capacity to do workCapacity to do work

Forms of energyForms of energy Potential energyPotential energy Kinetic energyKinetic energy Chemical energyChemical energy

What Can Cells Do What Can Cells Do with Energy?with Energy?

Cells use energy for:Cells use energy for: Chemical workChemical work

Mechanical workMechanical work

Electrochemical workElectrochemical work

First Law of ThermodynamicsFirst Law of Thermodynamics

The total amount of energy in the The total amount of energy in the universe remains constantuniverse remains constant

Energy can undergo conversions Energy can undergo conversions from one form to another, but it from one form to another, but it cannot be created or destroyedcannot be created or destroyed

One-Way Flow of EnergyOne-Way Flow of Energy

The sun is life’s primary energy sourceThe sun is life’s primary energy source

Producers trap energy from the sun Producers trap energy from the sun and convert it into chemical bond and convert it into chemical bond energyenergy

AllAll organisms use the energy stored in organisms use the energy stored in the bonds of organic compounds to do the bonds of organic compounds to do work work

Second Law of Second Law of ThermodynamicsThermodynamics

No energy conversion is ever 100 No energy conversion is ever 100

percent efficientpercent efficient

The total amount of energy is The total amount of energy is

flowing from high-energy forms to flowing from high-energy forms to

forms lower in energyforms lower in energy

EntropyEntropy

Measure of degree of disorder in a Measure of degree of disorder in a systemsystem

Energy Changes & Energy Changes & Cellular WorkCellular Work

Energy changes in cells tend to Energy changes in cells tend to run spontaneously in the direction run spontaneously in the direction that results in a decrease in usable that results in a decrease in usable

energyenergy

Endergonic ReactionEndergonic Reaction

+ 602 and 6H2O

Energy in

energy-poorstarting substances 6 12

glucose - a product with more energy

Figure 6.5a,bPage 100

Exergonic ReactionExergonic Reaction

Energy out

glucose - energy-rich starting

substance

+602

products with less energy

6 6

Figure 6.5a,bPage 100

Structure of ATPStructure of ATP

three phosphate groups

sugar (ribose)

nucleotide base (adenine)

Figure 6.6bPage 101

ATP: Main Energy CarrierATP: Main Energy Carrier

ATP/ADP cycle regenerates ATPATP/ADP cycle regenerates ATP

energyinput

ADP + Pi

ATP

energy output

Electron TransfersElectron Transfers

Oxidation - lose electronOxidation - lose electron

Reduction - gain electronReduction - gain electron

Central to the formation of ATP Central to the formation of ATP

during photosynthesis and aerobic during photosynthesis and aerobic

respiration respiration

Participants in Participants in Metabolic PathwaysMetabolic Pathways

Energy CarriersEnergy Carriers

EnzymesEnzymes

CofactorsCofactors

ReactantsReactants

IntermediatesIntermediates

ProductsProducts

Degradative and Anabolic Degradative and Anabolic PathwaysPathways

ATP

BIOSYNTHETIC PATHWAYS(ANABOLIC)

ENERGY INPUT

DEGRADATIVE PATHWAYS

(CATABOLIC)

energy-poor products

large energy-rich molecules

simple organic compounds

ADP + Pi

Types of Reaction SequencesTypes of Reaction Sequences

BRANCHING PATHWAY

LINEAR PATHWAY CYCLIC PATHWAY

A B C D EF

K J I G

N M L H

Figure 6.8Page 102

Which Way Will Which Way Will a Reaction Run?a Reaction Run?

Nearly all chemical reactions are Nearly all chemical reactions are

reversiblereversible

Chemical EquilibriumChemical Equilibrium

HIGHLYSPONTANEOUS

EQUILIBRIUM

HIGHLYSPONTANEOUS

RELATIVE CONCENTRATION

OF PRODUCT

RELATIVE CONCENTRATION

OF REACTANT

Figure 6.9Page 103

Chemical EquilibriumChemical Equilibrium

Energy in the reactants equals that Energy in the reactants equals that in the productsin the products

Product and reactant molecules Product and reactant molecules usually differ in energy contentusually differ in energy content

Therefore, at equilibrium, the Therefore, at equilibrium, the amount of reactant almost never amount of reactant almost never equals the amount of product equals the amount of product

No Vanishing AtomsNo Vanishing Atoms

Law of conservation of mass Law of conservation of mass

Reactions rearrange atoms, but they Reactions rearrange atoms, but they

never destroy themnever destroy them

As many atoms of each element in all As many atoms of each element in all

the products as there were in all the the products as there were in all the

reactantsreactants

Electron Transfer ChainsElectron Transfer Chains

Arrangement of enzymes, Arrangement of enzymes,

coenzymes, at cell membranecoenzymes, at cell membrane Works like a bucket brigade in Works like a bucket brigade in

fighting fires in that electrons are fighting fires in that electrons are transferred from a carrier to the next transferred from a carrier to the next in the cell membrane.in the cell membrane.

Enzyme Structure and FunctionEnzyme Structure and Function

Enzymes are catalytic moleculesEnzymes are catalytic molecules

They speed the rate at which reactions They speed the rate at which reactions approach equilibriumapproach equilibrium

Four Features of EnzymesFour Features of Enzymes1) Enzymes do not make anything 1) Enzymes do not make anything

happen that could not happen on its happen that could not happen on its own. They just make it happen own. They just make it happen much faster.much faster.

2) Reactions do not alter or use up 2) Reactions do not alter or use up enzyme molecules.enzyme molecules.

Four Features of EnzymesFour Features of Enzymes

3) The same enzyme usually works for 3) The same enzyme usually works for

both the forward and reverse both the forward and reverse reactions.reactions.

4) Each type of enzyme recognizes and 4) Each type of enzyme recognizes and binds to only certain substrates.binds to only certain substrates.

Activation EnergyActivation Energy

For a reaction For a reaction to occur, an to occur, an energy barrier energy barrier must be must be surmountedsurmounted

Enzymes make Enzymes make the energy the energy barrier smallerbarrier smaller

activation energywithout enzyme

activation energywith enzyme

energyreleased

by thereaction

products

starting substance

Figure 6.12aPage 105

Factors Influencing Factors Influencing Enzyme ActivityEnzyme Activity

Coenzymes and cofactorsCoenzymes and cofactors

regulatorsregulators

Temperature Temperature

pHpH

Salt concentrationSalt concentration

Effect of TemperatureEffect of Temperature

Small increase in Small increase in temperature increases temperature increases molecular collisions, molecular collisions, reaction ratesreaction rates

High temperatures High temperatures disrupt bonds and disrupt bonds and destroy the shape of destroy the shape of active site active site

Figure 6.17bPage 109

Effect of pHEffect of pH

Figure 6.17cPage 109

Beer, Enzymes, and Beer, Enzymes, and Your LiverYour Liver

Alcohol dehydrogenase Alcohol dehydrogenase

Acetaldehyde dehydrogenase Acetaldehyde dehydrogenase

Cytochrome and catalase Cytochrome and catalase

Heavy drinking destroys liver cells Heavy drinking destroys liver cells

and body’s ability to detoxify alcoholand body’s ability to detoxify alcohol