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Energy and MetabolismChapter 8

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Outline Flow of Energy in Living Things Laws of Thermodynamics Free Energy Activation Energy Enzymes

• Forms• Activity

ATP Biochemical Pathways

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Flow of Energy in Living Things

Energy - the capacity to do work• kinetic - energy of motion• potential - stored energy

Thermodynamics - changes in heat• calorie - heat required to raise the

temperature of one gram of water one degree Celsius• kilocalorie = 1000 calories

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Flow of Energy in Living Things

Oxidation - Reduction• Oxidation occurs when an atom or molecule

loses an electron.• Reduction occurs when an atom or molecule

gains an electron.• Redox reactions occur because every electron that

is lost by an atom through oxidation is gained by some other atom through reduction.

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Fig. 8.3 (TEArt)

Product

H

H

H

H

NAD+

NAD

NAD

H

Energy-rich molecule

1. Enzymes that harvesthydrogen atoms have abinding site for NAD+

located near anotherbinding site. NAD+ andan energy-richmolecule bind tothe enzyme.

3. NADH thendiffuses away andis available toother molecules.

2. In an oxidation-reduction reaction,a hydrogen atomis transferred toNAD+, formingNADH.

Enzyme

NAD+NAD+

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Laws of Thermodynamics

First Law of Thermodynamics• Energy cannot be created or destroyed, but

only change form.• During each conversion, some of the energy

dissipates into the environment as heat.• Heat is defined as the measure of the random

motion of molecules.

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Laws of Thermodynamics

Second Law of Thermodynamics• The disorder (entropy) in the universe is

continuously increasing.• Energy transformations proceed spontaneously to

convert matter from a more ordered, less stable form, to a less ordered, more stable form.

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Free Energy

Free energy refers to the amount of energy actually available to break and subsequently form other chemical bonds.• Gibbs’ free energy (G)

• change in free energy• endergonic - any reaction that requires an input of energy• exergonic - any reaction that releases free energy

Important Note: All reactions require an Activation Energy

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Activation Energy

Activation energy refers to the extra energy required to destabilize existing chemical bonds and initiate a chemical reaction.• catalyst - substance that lowers the activation

energy• cannot violate laws of thermodynamics.

• direction of a chemical reaction is determined solely by the difference in free energy between the reactants and the products

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Activation Energy and Catalysis

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Enzymes Are Biological Catalysts

Enzymes are proteins that carry out most catalysis in living organisms.• Unique three-dimensional shape enables an

enzyme to stabilize a temporary association between substrates.• Because the enzyme itself is not changed or

consumed in the reaction, only a small amount is needed, and can then be reused.

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Enzymes

Most enzymes are globular proteins with one or more active sites.• Substrates bind to the enzyme at these active

sites, forming an enzyme-substrate complex.• Often end in suffix ase but not always.

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Fig. 8.9 (TEArt)

The substrate,sucrose, consistsof glucose andfructose bondedtogether.

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The substratebinds to theenzyme, formingan enzyme-substratecomplex.

2

The binding ofthe substrateand enzymeplaces stress onthe glucose-fructose bond,and the bondbreaks.

3

Products arereleased, andthe enzyme isfree to bindothersubstrates.

4Bond

Enzyme

Active site

H2O

Glucose Fructose

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Enzyme Forms

A multienzyme complex is composed of several enzymes, catalyzing the different steps of a sequence of reactions, that are associated with one another.• subunits work in concert, providing significant

advantages in catalytic efficiency RNA catalysts “ribozymes”

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CARBONIC ANHYDRASE

Read about Carbonic Anhydrase

Page 149

How much does C.A increase the rate of reaction?

What is the “knife” in this enzyme?

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Pyruvate Dehydrogenase What does it do?

60 protein subunits, a very COMPLEX COMPLEX

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Factors Affecting Enzyme Activity

Temperature• Rate of an enzyme-catalyzed reaction

increases with temperature, but only up to an optimum temperature.

pH• Ionic interactions also hold enzymes together.

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Factors Affecting Enzyme Activity

Inhibitors and activators• inhibitor - substance that binds to an enzyme

and decreases its activity• competitive inhibitors - compete with the substrate

for the same active site• noncompetitive inhibitors - bind to the enzyme in a

location other than the active site• allosteric sites - specific binding sites acting as

on/off switches

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Factors Affecting Enzyme Activity

• activator - substances that bind to allosteric sites and keep the enzymes in their active configurations• increase enzyme activity

• cofactors - chemical components that facilitate enzyme activity (minerals)

• Coenzyme (vitamins)

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ATP

Adenosine triphosphate (ATP) is the chief energy currency of the cell.• Each molecule is a nucleotide composed of

ribose, adenine, and a triphosphate group.• energy stored in the triphosphate group

• cell uses ATP to drive endergonic reactions

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Biochemical Pathways

Biochemical pathways are the organizational units of metabolism.• Metabolism is the total of all chemical reactions

carried out by an organism.• anabolism- reactions that expend energy to make bonds• catabolism - reactions that harvest energy when bonds are

broken

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Regulation of Biochemical Pathways

Biochemical pathways must be coordinated and regulated to operate efficiently.• advantageous for cell to temporarily shut down

biochemical pathways when their products are not needed• feedback inhibition - When the cell produces increasing

quantities of a particular product, it automatically inhibits its ability to produce more.

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Feedback Inhibition

The Concept of REGULATION is a KEY CONCEPT in Biology

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Feedback Mechanisms

Negative Feedback- Brings the amount of final product back to a baseline

Positive Feedback- Brings the amount of product away from a baseline.

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Summary

Flow of Energy in Living Things Laws of Thermodynamics Free Energy Activation Energy Enzymes

• Forms• Activity

ATP Biochemical Pathways

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See Chapter 8 Animation “Feedback Inhibition of Biochemical Pathways