AP Biology Chapter 8: Metabolism and Enzymes. Kinetic Energy vs. Potential Energy

AP Biology

Chapter 8:Metabolism and Enzymes

Kinetic Energy vs. Potential Energy

Potential Energy vs. Kinetic Energy

Potential Energy vs. Kinetic Energy

Thermodynamics

LE 8-3

Chemical energy

Heat CO2

First law of thermodynamics Second law of thermodynamics

H2O

LE 8-7a

G = 0

A closed hydroelectric system

G < 0

LE 8-7b

An open hydroelectric system

G < 0

LE 8-7c

A multistep open hydroelectric system

G < 0G < 0

G < 0

LE 8-6a

Reactants

EnergyProducts

Progress of the reaction

Amount ofenergyreleased(G < 0)

Fre

e en

erg

y

Exergonic reaction: energy released

LE 8-6b

ReactantsEnergy

Products

Progress of the reaction

Amount ofenergyrequired(G > 0)

Fre

e en

erg

y

Endergonic reaction: energy required

Fig: 8.8

Phosphorylation

LE 8-11

NH2

Glu

P i

P i

P i

P i

Glu NH3

P

P

P

ATPADP

Motor protein

Mechanical work: ATP phosphorylates motor proteins

Protein moved

Membraneprotein

Solute

Transport work: ATP phosphorylates transport proteins

Solute transported

Chemical work: ATP phosphorylates key reactants

Reactants: Glutamic acidand ammonia

Product (glutamine)made

+ +

+

LE 8-15

Course ofreactionwithoutenzyme

EA

without enzyme

G is unaffectedby enzyme

Progress of the reaction

Fre

e en

erg

y

EA withenzymeis lower

Course ofreactionwith enzyme

Reactants

Products

LE 8-16

Substrate

Active site

Enzyme Enzyme-substratecomplex

LE 8-17

Enzyme-substratecomplex

Substrates

Enzyme

Products

Substrates enter active site; enzymechanges shape so its active siteembraces the substrates (induced fit).

Substrates held inactive site by weakinteractions, such ashydrogen bonds andionic bonds.

Active site (and R groups ofits amino acids) can lower EA

and speed up a reaction by• acting as a template for substrate orientation,• stressing the substrates and stabilizing the transition state,• providing a favorable microenvironment,• participating directly in the catalytic reaction.

Substrates areconverted intoproducts.

Products arereleased.

Activesite is

availablefor two new

substratemolecules.

R groups of Amino Acids

Optimal Performance

LE 8-19Substrate

Active site

Enzyme

Competitiveinhibitor

Normal binding

Competitive inhibition

Noncompetitive inhibitor

Noncompetitive inhibition

A substrate canbind normally to the

active site of anenzyme.

A competitiveinhibitor mimics the

substrate, competingfor the active site.

A noncompetitiveinhibitor binds to the

enzyme away from theactive site, altering the

conformation of theenzyme so that its

active site no longerfunctions.

LE 8-20a

Allosteric enzymewith four subunits

Regulatorysite (oneof four) Active form

Activator

Stabilized active form

Active site(one of four)

Allosteric activatorstabilizes active form.

Non-functionalactive site

Inactive formInhibitor

Stabilized inactive form

Allosteric inhibitorstabilizes inactive form.

Oscillation

Allosteric activators and inhibitors

LE 8-21

Active siteavailable

Initial substrate(threonine)

Threoninein active site

Enzyme 1(threoninedeaminase)

Enzyme 2

Intermediate A

Isoleucineused up bycell

Feedbackinhibition Active site of

enzyme 1 can’tbindtheoninepathway off

Isoleucinebinds toallostericsite

Enzyme 3

Intermediate B

Enzyme 4

Intermediate C

Enzyme 5

Intermediate D

End product(isoleucine)

LE 8-20b

Substrate

Binding of one substrate molecule toactive site of one subunit locks allsubunits in active conformation.

Cooperativity another type of allosteric activation

Stabilized active formInactive form

LE 5-20e

Chains

ChainsHemoglobin

IronHeme

CollagenPolypeptide chain

Polypeptidechain