Chapter 08 An Introduction to Metabolism

MetabolismMetabolism
Chapter 8
An Introduction
to Metabolism

Chapter 8
Learning ObjectivesLearning Objectives
• Apply fundamental laws of physics toApply fundamental laws of physics to
biological metabolismbiological metabolism
• Describe with chemical equations howDescribe with chemical equations how
chemical potential energy is stored andchemical potential energy is stored and
utilized in catabolic and anabolic reactionsutilized in catabolic and anabolic reactions
using appropriate vocabulary (endergonic,using appropriate vocabulary (endergonic,
exergonic, free energy)exergonic, free energy)
• Describe how enzymes work as catalysts toDescribe how enzymes work as catalysts to
lower activation energy.lower activation energy.
• Describe with examples how enzymes areDescribe with examples how enzymes are
regulated by physical and cellularregulated by physical and cellular
mechanisms.mechanisms.

Chapter 8
OutlineOutline
A.A. Forms of EnergyForms of Energy
B.B. Laws of ThermodynamicsLaws of Thermodynamics
C. Metabolic ReactionsC. Metabolic Reactions
D. ATPD. ATP
E. Metabolic PathwaysE. Metabolic Pathways
 Energy of ActivationEnergy of Activation
 EnzymesEnzymes
 PhotosynthesisPhotosynthesis
 Cellular Respiration.Cellular Respiration.
- Kinectic verses Potential
- Total energy is constant
- Entropy (disorder) increases
-exergonic versus endergonic reactions
- the intermediate form of chemical energy for most metabolic reactions
- an energy barrier
- catalysts: cells way of overcoming energy barriers
- using solar energy to create chemical bonds
-using the energy from photosynthesis
to create other chemical bonds

Flow of
Energy
Notes: 99.9% of all energy on
earth is derived from the sun

Chapter 8
Forms of EnergyForms of Energy

Chapter 8
A. Two Forms of EnergyA. Two Forms of Energy
a. Kinetic Energya. Kinetic Energy = Energy of motion= Energy of motion
Examples: ?Examples: ?
b. Potentialb. Potential EnergyEnergy = Stored Energy= Stored Energy(can create motion(can create motion))
Examples: ?Examples: ?
- falling water, rolling bycicle ………..
- water behind a dam, stretch elastic, drawn bow….ect
** Important (biology) type of potential energy = Chemical E.
Examples: oil, gasoline = fossil fuels
(notes: write a chemical equation that depicts combustion
of a hydrocarbon [C16H32SO4]
Know these two definitions.

Chapter 8
B. Laws of ThermodynamicsB. Laws of Thermodynamics
First law:First law: Conservation of energyConservation of energy
Energy cannot be created or destroyed, butEnergy cannot be created or destroyed, but
can only be changed from one type to anothercan only be changed from one type to another
Example: Think of the changes in forms of energy in the combustion reaction
you just diagramed
Know these two laws !

Chapter 8
Second law:Second law:
Law of increasing entropyLaw of increasing entropy (disorder)(disorder)
When energy is changed from one form toWhen energy is changed from one form to
another, there is aanother, there is a loss of usable energyloss of usable energy thatthat
goes to increase disordergoes to increase disorder
Example: The energy of combustion is largely dissipated as heat (Enthalpy) to
molecules in the “air” etc. as they begin to vibrate faster, spread out and expand.
(Entropy)

Energy flow in biosystems:
Carbohydrate metabolism
YOU MUST KNOW THIS EQUATION !
(and its reverse!)
A. Carbohydrate synthesis
B. Carbohydrate Metabolism
(Oxidative Respiration)
O2
These molecules are
More disordered than
glucose = increased
entropy
(reference p162)

Cells and Energy & Entropy
Stored
potential
energy
Increased
EntropyA
B
Both of these means of releasing energy result in an increased entropy
Electrogenic
Pumps

Chapter 8
Free energyFree energy
In biology,In biology, Free energyFree energy is considered insteadis considered instead
of entropyof entropy..
Definition:Definition:
Free Energy: “Gibb’s Free Energy”Free Energy: “Gibb’s Free Energy” (( G)G)
The amount of energy available to do workThe amount of energy available to do work
after a chemical reaction has occurred:after a chemical reaction has occurred:
the potential energy difference betweenthe potential energy difference between
reactants and products.reactants and products.

Chapter 8
Types of Reactions:Types of Reactions:
There are two types of reactions:There are two types of reactions:
1.1. Exergonic ReactionsExergonic Reactions - Products have- Products have lessless
free energyfree energy than reactants.than reactants.
2.2. Endergonic ReactionsEndergonic Reactions - Products have- Products have
moremore free energy than reactants.free energy than reactants.
TheseThese do not require energy inputdo not require energy input and generally proceedand generally proceed
(are sped up) simply with the help of an enzyme.(are sped up) simply with the help of an enzyme.
These reactionsThese reactions require energy inputrequire energy input, usually in the, usually in the
form high energy bonds from ATP, and also require theform high energy bonds from ATP, and also require the
actions of enzymesactions of enzymes..

Chapter 8
Two types of free energyTwo types of free energy
changes in Biologychanges in Biology
1.
Fig. 8.6 p 147

Chapter 8
2.
Fig. 8.6 p 147

Chapter 8
Metabolic Reactions andMetabolic Reactions and
Energy TransformationsEnergy Transformations
MetabolismMetabolism:: The total of all the reactions within aThe total of all the reactions within a
cell.cell.
A + BA + B  C + DC + D
(Reactants) (Products)
OR
b. Require energy input
= Endergonic reaction
a. Release energy to surroundings
= Exergonic reaction

Chapter 8
Free Energy Defined:Free Energy Defined:
Endergonic versus ExergonicEndergonic versus Exergonic
A. B.
Exergonic reaction:
G is said
to be negative
Endergonic reaction:
G is positive
= the energy difference between reactants and products, and is therefore
available (free) after the reaction has occurred. Reaction A- has more
available (positive), Reaction B – has less available (negative)
Require energy input
= Endergonic reaction
Release energy to surroundings
= Exergonic reaction

Chapter 8
How is this “Free Energy” used?How is this “Free Energy” used?
Metabolic reactions areMetabolic reactions are coupledcoupled to the generationto the generation
and release of a high energy intermediate:and release of a high energy intermediate:
Adenosine triphosphateAdenosine triphosphate ((ATPATP))
 Energy released by anEnergy released by an exergonicexergonic reaction captured inreaction captured in
ATPATP
 That ATP used to drive anThat ATP used to drive an endergonicendergonic reactionreaction

The ATP Cycle
Mechanical work
Chemical work
H2O
H2O
** ATP is “coupled
To virtually all
Metabolic reactions

Energy
summary:
• Photo synthesis captures energy from the sun an transfers it to
chemical bond.
• Cellular respiration (an exergonic reaction) releases the energy from
these bonds and couples it to one of two processes:
1. High energy phosphate bonds of ATP (“substrate level phosphorylation”)
2. Proton gradient – followed by ATP production
• Synthesis reactions are endergonic and require an input of energy
from ATP produced in exergonic reactions.
• Other endergonic reactions include muscular movement, and also
require an energy input from ATP (and other high energy phosphate
containing molecules. Ex: phosphocreatine)

Chapter 8
Work-Related FunctionsWork-Related Functions
of ATPof ATP
Primarily to perform cellular workPrimarily to perform cellular work
1.1. Chemical Work - Energy needed toChemical Work - Energy needed to
synthesize macromoleculessynthesize macromolecules
2.2. Transport Work - Energy needed to pumpTransport Work - Energy needed to pump
substances across plasma membranesubstances across plasma membrane
3.3. Mechanical Work - Energy needed toMechanical Work - Energy needed to
contract muscles, beat flagella, etccontract muscles, beat flagella, etc
Know 3 forms of work coupled to ATP

Chapter 8
Types of Cellular Work associated with ATPTypes of Cellular Work associated with ATP
Fig. 8.10 p 151

Chapter 8
Metabolic PathwaysMetabolic Pathways
Reactions usually occur in a sequenceReactions usually occur in a sequence
 Products of an earlier reaction become reactants of a laterProducts of an earlier reaction become reactants of a later
reactionreaction
 Such linked reactions form aSuch linked reactions form a metabolic pathwaymetabolic pathway
Begins with a particularBegins with a particular reactantreactant,,
Proceeds through severalProceeds through several intermediatesintermediates, and, and
Terminates with a particularTerminates with a particular end productend productis required at each step……
“A” is Initial
Reactant
“D” is End
Product
Intermediates

Chapter 8
What is an enzyme?What is an enzyme?
EnzymesEnzymes
 Protein molecules thatProtein molecules that function as catalystsfunction as catalysts
 CatalystCatalyst = any molecule that speeds up a reaction= any molecule that speeds up a reaction
but is itself not used up in that reaction.but is itself not used up in that reaction.
 The things it acts on are calledThe things it acts on are called substratessubstrates
 Each enzyme accelerates a specific reactionEach enzyme accelerates a specific reaction
 Each reaction in a metabolic pathway requires aEach reaction in a metabolic pathway requires a
unique and specific enzymeunique and specific enzyme
 End product will not appear unless ALL enzymes areEnd product will not appear unless ALL enzymes are
present and functionalpresent and functional
E1 E2 E3 E4 E5 E6
A  B  C  D  E  F  G
Definition:

Chapter 8
Enzymes:Enzymes:
How do they function.How do they function.
There is usually an input of energy requiredThere is usually an input of energy required
for two substrates to “meet” in anfor two substrates to “meet” in an
orientation that favors a reaction.orientation that favors a reaction.
This energy requirement is called:This energy requirement is called: Energy ofEnergy of
Activation.Activation.
Enzymes operate byEnzymes operate by lowering the energy oflowering the energy of
activationactivation (1)(1)
They do this by bringing the substrates intoThey do this by bringing the substrates into
contact with one another in the correctcontact with one another in the correct
orientation.orientation.
Energy of Activation

Chapter 8
Lining up substrate moleculesLining up substrate molecules

Chapter 8
2. Enzyme-Substrate Complex2. Enzyme-Substrate Complex
TheThe Induced fit model.Induced fit model.
• The enzyme and the substrate form a short livedThe enzyme and the substrate form a short lived
intermediate called theintermediate called the enzyme-substrate complex.enzyme-substrate complex.
• The substrates are bound inThe substrates are bound in the active sitethe active site. Binding. Binding
of the substrateof the substrate inducesinduces the active site tothe active site to changechange
conformationconformation, energetically aligning the substrates, energetically aligning the substrates
reactive sites.reactive sites.

Induced Fit
Model
Active site participates temporar
in the chemical energy transfer.
Fig. 8.15 p 153

Chapter 8
Enzymes:Enzymes:
A summary…………A summary…………
MECHANISMS
1. Catalysts (speed up reaction without being consumed)
They do this by “Lowering the Energy of Activation” (Ea)
- Decreased Ea results from….
a. Substrates are aligned to optimize new bond formation
b. Enzyme undergoes a conformational change (Induced fit)
e. Lower energy intermediates are formed. “Enzyme-substrate complex”
- (to be continued)

Chapter 8
Degradation vs. SynthesisDegradation vs. Synthesis
Degradation:Degradation:
EnzymeEnzyme complexes with a singlecomplexes with a single substratesubstrate
moleculemolecule
Substrate is broken apart into two productSubstrate is broken apart into two product
moleculesmolecules
Synthesis:Synthesis:
EnzymeEnzyme complexes with twocomplexes with two substratesubstrate
moleculesmolecules
Substrates are joined together and releasedSubstrates are joined together and released
as single product moleculeas single product molecule

Degradation vs.
Synthesis
Catabolic reaction.
Anabolic reaction.

Chapter 8
Factors Affecting Enzyme Activity (1)Factors Affecting Enzyme Activity (1)
a) Substrate concentrationa) Substrate concentration
Enzyme activity increases with substrateEnzyme activity increases with substrate
concentrationconcentration
More collisions between substrate moleculesMore collisions between substrate molecules
and the enzymeand the enzyme
b) Temperatureb) Temperature
Enzyme activity increases with temperatureEnzyme activity increases with temperature
Warmer temperatures cause more effectiveWarmer temperatures cause more effective
collisions between enzyme and substratecollisions between enzyme and substrate
However, hot temperatures destroy enzymeHowever, hot temperatures destroy enzyme
C pHC pH
Most enzymes are optimized for a particularMost enzymes are optimized for a particular
pHpH

Factors Affecting Enzyme Activity:
Temperature

pH
Fig. 8.16 p155

Chapter 8
Enzymes:Enzymes:
A summary…………A summary…………
A. MECHANISMS
1. Catalysts (speed up reaction)
Lower energy of activation
a) Align substrates
b) Undergo a conformational change (Induced fit)
c) Active site participates in the reaction
B. ACTIVITY
1. Synthesis and degradation: 2 substrates for synthesis, 1 for
degradation
2. Activity is affected by substrate conc. , Temperature, pH
- -

Chapter 8
Cellular Factors Affecting Enzyme ActivityCellular Factors Affecting Enzyme Activity
Cells can affect presence/absence of enzymeCells can affect presence/absence of enzyme
Cells can affect concentration of enzymeCells can affect concentration of enzyme
Cells can activate or deactivate enzymeCells can activate or deactivate enzyme
Molecules required to activate enzymeMolecules required to activate enzyme
 EnzymeEnzyme CofactorsCofactors areare inorganicinorganic elements andelements and
compounds. Ex. = Calcium, Magnesium, Zinccompounds. Ex. = Calcium, Magnesium, Zinc
 CoenzymesCoenzymes are organic cofactors, like someare organic cofactors, like some
vitaminsvitamins
 PhosphorylationPhosphorylation – some enzymes require– some enzymes require
addition of a phosphateaddition of a phosphate

Thiamine (Vitamine B1)
Riboflavine (Vitamine B2)
Coenzymes
Cu ++
Zn++
Mg++
Fe++
Cofactors

Chapter 08 An Introduction to Metabolism

ENZYMES ARE INDUCABLE!ENZYMES ARE INDUCABLE!

Activation by Phosphorylation

Chapter 8
Enzyme Inhibition.Enzyme Inhibition.
ReversibleReversible enzyme inhibitionenzyme inhibition
When a substance known as an inhibitor
binds to an enzyme and decreases its activity
-Competitive inhibitioninhibition – substrate and the– substrate and the
inhibitor are both able toinhibitor are both able to bind tobind to active siteactive site
- Noncompetitive inhibitionNoncompetitive inhibition – the inhibitor binds– the inhibitor binds
not at the active site, but atnot at the active site, but at thethe allosteric siteallosteric site
Feedback inhibitionFeedback inhibition – The– The end productend product of aof a
pathway inhibits the pathway’s first enzymepathway inhibits the pathway’s first enzyme

Chapter 8
Competitive enzyme InhibitionCompetitive enzyme Inhibition
Fig. 8.18 p 156

Chapter 8
B: Non-competitiveB: Non-competitive
(Allosteric)(Allosteric)
Note: there are also
Allosteric activators
** See fig. 8.20
Page 158 in your text

Feedback Inhibition
Fig. 8.21 p 159

Hypothalamal-Pituitary AxisHypothalamal-Pituitary Axis

Chapter 8
Irreversible InhibitionIrreversible Inhibition
Materials that irreversibly inhibit an enzymeMaterials that irreversibly inhibit an enzyme
are known asare known as poisonspoisons
CyanidesCyanides inhibit enzymes resulting in all ATPinhibit enzymes resulting in all ATP
productionproduction
PenicillinPenicillin inhibits an enzyme unique to certaininhibits an enzyme unique to certain
bacteriabacteria
Heavy metalsHeavy metals irreversibly bind with manyirreversibly bind with many
enzymesenzymes
Nerve gasNerve gas irreversibly inhibits enzymesirreversibly inhibits enzymes
required by nervous systemrequired by nervous system

Chapter 8
A. MECHANISMS
-Catalysts (speed up reaction)
- Lower energy of activation
-Form intermediate “Enzyme-substrate complex”
- Undergo a conformational change (Induced fit)
- Active site participates in the reaction
B. ACTIVITY
- Synthesis and degradation: 2 substrates for synthesis, 1 for degredation
-Activity is affected by substrate conc. , Temperature, Ph
C. REGULATION
- Production and activation is regulated by cells (inducable enzymes)
-May require co-enzymes OR co-factors from a nutrient source
-May be regulated by other enzymes (phosphorylation turns off or on)
-Are subject to reversible and irreversible inhibition.
-Reversible: Competitive, Non-competitive, Feedback inhibition.
- Poisons such as cyanide are irreversible inhibitors

Chapter 8
How is all this energy (ATP) generated ?How is all this energy (ATP) generated ?
Oxidation-ReductionOxidation-Reduction
Oxidation-reductionOxidation-reduction ((redoxredox)) reactions:reactions:
Electrons pass from one molecule to anotherElectrons pass from one molecule to another
- The molecule that loses an electron isThe molecule that loses an electron is oxidizedoxidized
- The molecule that gains an electron isThe molecule that gains an electron is reducedreduced
Both take place at same timeBoth take place at same time
One molecule accepts the electron given upOne molecule accepts the electron given up
by the otherby the other
LEO (the lion) says GER
“Loss of Electrons = Oxidation”
“Gain of Electrons = Reduction”
Redox reactions

PhotosynthesisPhotosynthesis
andand
Cellular RespirationCellular Respiration
Carbon dioxideCarbon dioxide
+water+water
+solar energy+solar energy
GlucoseGlucose
+oxygen+oxygen
6CO6CO22 + 6H+ 6H22OO
energyenergy
 CC66HH1212OO66 + 6O+ 6O22
Carbon dioxideCarbon dioxide
+water+water
+chemical energy+chemical energy
GlucoseGlucose
+oxygen+oxygen 
6CO6CO22 + 6H+ 6H22O + energyO + energyCC66HH1212OO66 + 6O+ 6O22
Cellular Respiration:Cellular Respiration:
Photosynthesis:Photosynthesis:
Both are coupled to a redox chain that passes energy on to ATP synthesis

Chapter 8
Electron Transport ChainElectron Transport Chain
Membrane-bound carrier proteins found inMembrane-bound carrier proteins found in
mitochondria and chloroplastsmitochondria and chloroplasts
Physically arranged in an ordered seriesPhysically arranged in an ordered series
 Starts with high-energy electrons and low-energyStarts with high-energy electrons and low-energy
ADPADP
 Pass electrons from one carrier to anotherPass electrons from one carrier to another
- Electron energy used to pump hydrogen ions (HElectron energy used to pump hydrogen ions (H++
) to one) to one
side of membraneside of membrane
- Establishes electrical gradient across membraneEstablishes electrical gradient across membrane
- Electrical gradient used to make ATP from ADP –Electrical gradient used to make ATP from ADP –
ChemiosmosisChemiosmosis
 Ends with low-energy electrons and high-energy ATPEnds with low-energy electrons and high-energy ATP

A Metaphor for the
Electron Transport Chain
H+
gradient

Oxidative phosphorylation
(Oxidative phosphorylation refers specifically to the use of a hydrogen ion gradient)

Chapter 8
OutlineOutline
A.A. Forms of EnergyForms of Energy
B.B. Laws of ThermodynamicsLaws of Thermodynamics
C. Metabolic ReactionsC. Metabolic Reactions
D. ATPD. ATP
E. Metabolic PathwaysE. Metabolic Pathways
 Energy of ActivationEnergy of Activation
 EnzymesEnzymes
 PhotosynthesisPhotosynthesis
 Cellular RespirationCellular Respiration
- Kinectic verses Potential
- Total energy is constant
- Entropy (disorder) increases
-exergonic versus endergonic reactions
- the intermediate form of chemical energy for most metabolic reactions
- an energy barrier
- catalysts: cells way of overcoming energy barriers
- using solar energy to create chemical bonds
-using the energy from photosynthesis
to create other chemical bonds

An Introduction
to Metabolism
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Chapter 08 An Introduction to Metabolism

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Chapter 08 An Introduction to Metabolism