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Ch 8 Cellular Metabolism How cells utilize energy

Ch 8 Cellular Metabolism How cells utilize energy

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Page 1: Ch 8 Cellular Metabolism How cells utilize energy

Ch 8 Cellular MetabolismHow cells utilize energy

Page 2: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-2On the platform,the diver hasmore potentialenergy.

Diving convertspotentialenergy to kinetic energy.

Climbing up convertskinetic energy ofmuscle movement topotential energy.

In the water, the diver has lesspotential energy.

Page 3: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-3

Chemical energy

Heat CO2

First law of thermodynamics Second law of thermodynamics

H2O

Page 4: Ch 8 Cellular Metabolism How cells utilize energy

The First Law of Thermodynamics

– Energy cannot be created or destroyed – Energy can be transferred and transformed

Principle of conservation of energy

Page 5: Ch 8 Cellular Metabolism How cells utilize energy

The Second Law of Thermodynamics

• Every energy transfer or transformation increases the entropy (disorder) of the universe

• Because some energy is lost as heat (unusable)

Page 6: Ch 8 Cellular Metabolism How cells utilize energy

• Metabolism– an organism’s (or cell’s) total chemical reactions

Name a common cellular reaction.

Two kinds of reactions:

Catabolism (catabolic rxn)

Breakdown of a larger molecule into smaller lower energy productsReleases of energyExergonic rxn

Anabolism (anabolic rxn)Synthesis of larger high energy molecules fromlower energy reactantsRequires input of energyEndergonic reactions

Page 7: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-12

Pi

ADP

Energy for cellular work

(endergonic, energy-

consuming processes)

Energy from catabolism

(exergonic, energy-

yielding processes)

ATP

+

Cellular energy used for:transport (across membranes)mechanical work (motility, contraction)enzymatic activity (catalysis of reactions)

Page 8: Ch 8 Cellular Metabolism How cells utilize energy

Catabolic rxn

C6H12O6 + 6O2 ----> 6CO2 + 6H2O + ATPglucose

Exergonic

Anabolic rxn

6CO2 + 6H2O ----> C6H12O6 + 6O2

glucose

Endergonic

Light

Examples

Page 9: Ch 8 Cellular Metabolism How cells utilize energy

Biological rxns

-Catalyzed by enzymes

-Often arranged in multiple steps called pathways

Page 10: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-UN141

Enzyme 1

A B

Reaction 1

Enzyme 2

C

Reaction 2

Enzyme 3

D

Reaction 3

ProductStarting

molecule

Enzymatic Pathway

Page 11: Ch 8 Cellular Metabolism How cells utilize energy

Enzymes

Biological catalysts

Increase rate of reactionsby lowering activation energy (EA)

Spontaneous reactions can take a long time!Need enzymes to speed reactions for cell survival

Page 12: Ch 8 Cellular Metabolism How cells utilize energy

Activation Energy (EA)

• Needed to destabilize bonds of reactants

Page 13: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-14

Transition state

C D

A B

EA

Products

C D

A B

G < O

Progress of the reaction

Reactants

C D

A B

Fre

e en

erg

y

Could raise temp.to break bonds

Page 14: Ch 8 Cellular Metabolism How cells utilize energy

Why don’t cells rely on increases in temperature to break bonds?

Denaturation of proteins and damage to the cell.

Page 15: Ch 8 Cellular Metabolism How cells utilize energy

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

Page 16: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-13

SucroseC12H22O11

GlucoseC6H12O6

FructoseC6H12O6

Example:

Page 17: Ch 8 Cellular Metabolism How cells utilize energy

Structure & Function of Enzyme DRAW

• Enzymes bind substrate molecules (the reactant)

• Substrates bind to active site on enzyme

• Binding induces conformational change in enzyme--better ”fit” for substrate

• Active sites are highly specific and discriminatory i.e. sucrase does not accept lactose

Page 18: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-16

Substrate

Active site

Enzyme Enzyme-substratecomplex

Page 19: Ch 8 Cellular Metabolism How cells utilize energy

How does enzyme lower activation energy of reaction?

– Orients substrates for optimal interaction

–Strains substrate bonds

–Provides a favorable microenvironment

-Covalently bonds to the substrate

Page 20: Ch 8 Cellular Metabolism How cells utilize energy

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.

Page 21: Ch 8 Cellular Metabolism How cells utilize energy

How do we know when a reaction is exergonic or endergonic?

Measure the system’s ability to perform work (usable energy)at uniform temperature and pressure.

Change in Gibbs free energy (G)

G= H-TS

Where H= change in total energy of the system, or enthalpy

T=absolute temperature in Kelvin (oC+273)

S =change in entropy (a measure of disorder)

Page 22: Ch 8 Cellular Metabolism How cells utilize energy

Another way to think about the state of energy in a cell is before and after a particular reaction occurs

G = G final state - G initial state

If the reaction gives final products that have less energy than the initial reactants, is G negative or positive?

The reverse?

When G < 0, the reaction is exergonic and spontaneous.

When G > 0, the reaction is endergonic and not spontaneous.

(products) (reactants)

Page 23: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-6a

Reactants

Energy

Products

Progress of the reaction

Amount ofenergy

released(G < 0)

Fre

e en

erg

y

Exergonic reaction: energy released

Catabolic rxn

C6H12O6 + 6O2 ----> 6CO2 + 6H2O + ATPglucose

Page 24: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-6b

ReactantsEnergy

Products

Progress of the reaction

Amount ofenergy

required(G > 0)

Fre

e en

erg

y

Endergonic reaction: energy required

Anabolic rxn

6CO2 + 6H2O ----> C6H12O6 + 6O2

glucose

Light

Page 25: Ch 8 Cellular Metabolism How cells utilize energy

Relationship among Free Energy, Instability, and Equilibrium

• Free energy:– a measure of a system’s instability, its tendency to change to a

more stable state

• During a spontaneous change– free energy decreases and the stability of a system increases

• Equilibrium is a state of maximum stability (G=0)

• If the metabolism of a cell is at equilibrium, what has occurred?

RIP

Page 26: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-12

Pi

ADP

Energy for cellular work

(endergonic, energy-

consuming processes)

Energy from catabolism

(exergonic, energy-

yielding processes)

ATP

+

Cellular energy used for:transport (across membranes)mechanical work (motility, contraction)enzymatic activity (catalysis of reactions)

Page 27: Ch 8 Cellular Metabolism How cells utilize energy

ATP structure

• ATP– adenosine triphosphate

• cellular energy carrier

Page 28: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-8

Phosphate groups

Ribose (sugar)

Adenine (base)

ATP structure Adenosine triphosphate

Cellular energy currency

Page 29: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-9

Adenosine triphosphate (ATP)

Energy

P P P

PPP i

Adenosine diphosphate (ADP)Inorganic phosphate

H2O

+ +

Page 30: Ch 8 Cellular Metabolism How cells utilize energy

• Terminal phosphate bond (ATP--> ADP + Pi)– Hydrolysis of “high energy” phosphate bond

• Energy is released (exergonic)• ADP lower energy than ATP• Why?

• Is ADP more stable than ATP? Explain.

Page 31: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-8

Phosphate groups

Ribose

Adenine

Page 32: Ch 8 Cellular Metabolism How cells utilize energy

• Energy from ATP hydrolysis – drives endergonic reactions

• Overall, coupled reactions are exergonic

Page 33: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-10

Endergonic reaction: G is positive, reactionis not spontaneous

Exergonic reaction: G is negative, reactionis spontaneous

G = +3.4 kcal/mol

G = –7.3 kcal/mol

G = –3.9 kcal/mol

NH2

NH3Glu Glu

Glutamicacid

Coupled reactions: Overall G is negative;together, reactions are spontaneous

Ammonia Glutamine

ATP H2O ADP P i

+

+ +

Page 34: Ch 8 Cellular Metabolism How cells utilize energy

How ATP Performs Work• Inorganic phosphate from ATP hydrolysis

– Transferred to target molecule• Called phosphorylation • Creates highly reactive, unstable target molecule• More prone to do “work” or change (conformation)

– Mechanical, transport, enzymatic

Page 35: Ch 8 Cellular Metabolism How cells utilize energy

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

+ +

+

Page 36: Ch 8 Cellular Metabolism How cells utilize energy

Regeneration of ATP

• ADP + P i--> ATP

– Energy for ADP phosphorylation from catabolic reactions

Page 37: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-12

Pi

ADP

Energy for cellular work

(endergonic, energy-

consuming processes)

Energy from catabolism

(exergonic, energy-

yielding processes)

ATP

+

Page 38: Ch 8 Cellular Metabolism How cells utilize energy

Environmental Conditions Affect Enzyme Function

?

Temperature: cold-->decreased chance of bumping into substratehot--> good chance of substrate interaction but

chance of denaturation at some point

pH->change in charge (H+ or OH-) can denature proteins and substrate

Examples of pH sensitive enzymes?

Page 39: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-18

Optimal temperature fortypical human enzyme

Optimal temperature forenzyme of thermophilic (heat-tolerant bacteria)

Temperature (°C)

Optimal temperature for two enzymes

0 20 40 60 80 100

Ra

te o

f re

ac

tio

n

Optimal pH for pepsin(stomach enzyme)

Optimal pHfor trypsin(intestinalenzyme)

pH

Optimal pH for two enzymes

0

Ra

te o

f re

ac

tio

n

1 2 3 4 5 6 7 8 9 10

What isyournormalbodytemp.?

Page 40: Ch 8 Cellular Metabolism How cells utilize energy

Cofactors• Non-protein enzyme helpers (like metals (Fe))

•Coenzymes•organic cofactors

•Vitamins •e.g. Vitamin K: required for blood clotting &

Required in certain carboxylation reactions

Page 41: Ch 8 Cellular Metabolism How cells utilize energy

Regulation of EnzymesEnzyme Inhibitors

• Competitive inhibitor– binds to active site of enzyme– blocks substrate binding by competition

•Noncompetitive inhibitor– binds to another part of enzyme– causes enzyme to change shape– prevents active site from binding substrate–Allosteric effect

DRAW

Page 42: Ch 8 Cellular Metabolism How cells utilize energy

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.

Page 43: Ch 8 Cellular Metabolism How cells utilize energy

Allosteric Regulation of Enzymes

• Where protein function at one site is affected by binding of a regulatory molecule at another site

• May inhibit or stimulate enzyme activity

Page 44: Ch 8 Cellular Metabolism How cells utilize energy

Allosteric Activation and Inhibition

• Most allosterically regulated enzymes are made from polypeptide subunits

• active and inactive forms

• binding of activator stabilizes active form of enzyme

• binding of inhibitor stabilizes inactive form of enzyme

Page 45: Ch 8 Cellular Metabolism How cells utilize energy

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

Page 46: Ch 8 Cellular Metabolism How cells utilize energy

• Cooperativity– form of allosteric regulation that can amplify enzyme

activity

• binding of substrate to one active site stabilizes favorable conformational changes at all other subunits

Page 47: Ch 8 Cellular Metabolism How cells utilize energy

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

Page 48: Ch 8 Cellular Metabolism How cells utilize energy

Feedback Inhibition

• End product of a metabolic pathway shuts down the pathway

• Prevents over-production of unneededmolecules

Page 49: Ch 8 Cellular Metabolism How cells utilize energy

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)

Page 50: Ch 8 Cellular Metabolism How cells utilize energy

Metabolic regulation influenced by cellular localization

• Cellular structures organize and concentrate enzymes in pathways– Membranes, organelles (mitochondria, chloroplast)

Page 51: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-22

Mitochondria,sites of cellular respiration

1 µm

Page 52: Ch 8 Cellular Metabolism How cells utilize energy

LE 8-22

It’s nice to get so much attention!