Chapter 6: Energy and Metabolism

Biological Work Requires Energy

• Remember to study the terms

• Energy Concepts Video

Fig. 8-2

Climbing up converts the kineticenergy of muscle movementto potential energy.

A diver has less potentialenergy in the waterthan on the platform.

Diving convertspotential energy tokinetic energy.

A diver has more potentialenergy on the platformthan in the water.

2 Laws of Thermodynamics

• 1.) Energy cannot be created or destroyed, but it can be transferred or changed from 1 form to another

• Photosynthesis:– Sun’s energy chemical energy in bonds of carbs– Later

• Chemical energy cellular work OR mechanical energy

• 2.) energy is converted from 1 from to another; some usable energy is converted to heat (disperses into surroundings)

• SO – total amount of energy available to do work is decreasing over time

• Total amount of energy overall remains constant

Fig. 8-3

(a) First law of thermodynamics (b) Second law of thermodynamics

Chemicalenergy

Heat CO2

H2O+

Entropy

• Measure of disorder or randomness• Less-usable energy is more disorganized• Organized = low entropy• Disorganized = high entropy

– Ex: heat• Entropy – continuously increasing in universe

in all natural processes– As more heat is released, our universe becomes

more disorganized

Enthalpy

• Total potential energy of the system

Free Energy

• Amount of energy available to do work under the conditions of a biochemical reaction

H = G + TS

• H = enthalpy• G = free energy• T = absolute temperature in K• S = entropy• Can’t effectively measure total free energy but

can measure CHANGES, so ΔG = ΔH - TΔS

Reactions

• Exergonic – release energy HL• Endergonic – gain energy from surroundings• Activation energy – needed to start a reaction• Coupled reaction – endergonic + exergonic

– exergonic reaction provides energy required to drive endergonic reaction

Fig. 8-6

Reactants

Energy

Free

ene

rgy

Products

Amount ofenergyreleased(∆G < 0)

Progress of the reaction(a) Exergonic reaction: energy released

Products

ReactantsEnergy

Free

ene

rgy Amount of

energyrequired(∆G > 0)

(b) Endergonic reaction: energy requiredProgress of the reaction

Enzymes – How Enzymes Work Video

• Enzyme – protein catalyst– Lower activation energy

• Catalyst– Speed up reaction

• Substrate – substance that enzyme acts on• Enzyme-Substrate complex –

– Enzymes orders structure of substrate– Gets reaction going– When breaks product + original enzyme

Enzymes

• Active site – on enzyme, where substrate binds

• Induced Fit – substrate binds, changes shape of enzyme– Enzyme and substrate not exactly complementary

Fig. 8-17

Substrates

Enzyme

Products arereleased.

Products

Substrates areconverted toproducts.

Active site can lower EAand speed up a reaction.

Substrates held in active site by weakinteractions, such as hydrogen bonds andionic bonds.

Substrates enter active site; enzyme changes shape such that its active siteenfolds the substrates (induced fit).

Activesite is

availablefor two new

substratemolecules.

Enzyme-substratecomplex

5

3

21

6

4

Enzymes

• Some – all protein• Some – 2 parts – work together to function

– 1) protein = apoenzyme– 2) chemical component = cofactor ( C or no C)

– Coenzyme – C, nonpolypeptide• Binds to apoenzyme as cofactor

Enzymes are most Effective At Certain Conditions

• Temperature– Most – temp increases, reaction rate increases– Low temp = slow– Too high temp. – denatures enzymes

• pH – enzyme active in narrow range• Charge – affect ionic bonds for tertiary and

quaternary structure

Fig. 8-18

Rat

e of

reac

tion

Optimal temperature forenzyme of thermophilic

(heat-tolerant) bacteria

Optimal temperature fortypical human enzyme

(a) Optimal temperature for two enzymes

(b) Optimal pH for two enzymes

Rat

e of

reac

tion

Optimal pH for pepsin(stomach enzyme)

Optimal pHfor trypsin(intestinalenzyme)

Temperature (ºC)

pH543210 6 7 8 9 10

0 20 40 80 60 100

Concentrations of Enzyme and Substrate

• Lots substrate – enzyme concentration limits• Less substrate than enzyme – substrate

concentration limits

Enzyme Activity

• Feedback Inhibition– Formation of a product inhibits an earlier reaction

in the sequence of reactions

– A B C D E

– When E is low – sequence proceeds rapidly– E is high – E1 slows and can stop entire sequence

Fig. 8-UN1

Enzyme 1 Enzyme 2 Enzyme 3DCBA

Reaction 1 Reaction 3Reaction 2Startingmolecule

Product

• Allosteric Regulation– Substance binds to enzyme’s allosteric site,

changing shape of active site and modifying enzyme’s activity

– Allosteric site = receptor site on enzyme, not active site

– Allosteric regulators – affect enzyme activity by binding to allosteric sites

• Keep inactive• activate

Fig. 8-20 Allosteric enyzmewith four subunits

Active site(one of four)

Regulatorysite (oneof four)

Active formActivator

Stabilized active form

Oscillation

Non-functionalactivesite

InhibitorInactive form Stabilized inactiveform

(a) Allosteric activators and inhibitors

Substrate

Inactive form Stabilized activeform

(b) Cooperativity: another type of allosteric activation

Enzyme Inhibition – can be inhibited or destroyed by certain chemicals

• Reversible Inhibition – inhibitor forms weak chemical bonds w/ enzyme– Competitive – inhibitor competes w/ normal

substrate for active site• No permanent damage

– Noncompetitive – inhibitor binds w/ enzyme but not at active site

• e enzymes by altering shape

Fig. 8-19

(a) Normal binding (c) Noncompetitive inhibition(b) Competitive inhibition

Noncompetitive inhibitor

Active siteCompetitive inhibitor

Substrate

Enzyme

• Irreversible Inhibition – inhibitor permanently inactivates or destroys an enzyme when it combines w/ enzyme at active site or elsewhere– Ex: poison

• Mercury, lead, nerve gas, cyanide