Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Two Forms of Energy

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Module 2D

Module 2D -- Energy and MetabolismEnergy and Metabolism

All living organisms require energy

for survival. In this module we will

examine some general principles

about chemical reactions and

energy usage within cells.

1

Objective # 19 Objective # 19

Define the term “energy”

and distinguish between

gg

potential and kinetic energy.

2

Objective 19 Objective 19

Energy is the ability to cause change. Energy is the ability to cause change.

Any change in the universe requires Any change in the universe requires energy. Energy comes in 2 forms: energy. Energy comes in 2 forms:

¾

¾Potential energyPotential energy is stored energy. No gg is stored energy. No gg

change is currently taking place change is currently taking place

¾

¾Kinetic energyKinetic energy is currently causing is currently causing

change. This always involves some change. This always involves some type of motion.

type of motion.

3

Two Forms of Energy Objective 19

Objective 19

4

Potential energy Kinetic energy

State the first and second laws

of thermodynamics and explain

h

l

li i

h

l

li i

how they apply to living

organisms.

5 Objective 20 Objective 20

ThermodynamicsThermodynamics is the study of is the study of

energy changes. energy changes.

Two fundamental laws govern allTwo fundamental laws govern all

Two fundamental laws govern all Two fundamental laws govern all

energy changes in the universe. These energy changes in the universe. These 2 laws are simply called the first and 2 laws are simply called the first and second laws of thermodynamics: second laws of thermodynamics:

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First Law:First Law: ¾

¾Energy can be converted from one Energy can be converted from one

form to another, but it cannot be form to another, but it cannot be created or destroyed.

created or destroyed.

¾

¾The total amount of energy in a closed The total amount of energy in a closed

system remains constant. system remains constant.

7

Second Law:Second Law: ¾

¾Whenever an energy conversion takes Whenever an energy conversion takes

place, some of the energy gets place, some of the energy gets converted into a more dispersed and converted into a more dispersed and pp less useful form (usually random less useful form (usually random molecular motion = heat). molecular motion = heat).

8

Free energyFree energy (G) is a measure of the (G) is a measure of the

amount of energy available to do amount of energy available to do useful work. It depends on: useful work. It depends on:

¾

¾the total amount of energy present; the total amount of energy present; g pg p

this is called

this is called enthalpyenthalpy (H)(H)

¾

¾the amount of energy being used for the amount of energy being used for

non

non--useful work (random molecular useful work (random molecular motion); this is called

motion); this is called entropyentropy (S).(S).

9

In general, In general, ΔΔG = G = ΔΔH H -- T T ΔΔS, where S, where TT

represents the temperature in degrees represents the temperature in degrees Kelvin and

Kelvin and ΔΔ represent “the change represent “the change in”.

in”.

This means the amount of energy This means the amount of energy

available for useful work (G) equals available for useful work (G) equals the total energy present (H)

the total energy present (H) minusminus the the energy that is being wasted on random energy that is being wasted on random molecular motion (S). molecular motion (S). 10 Objective 20 Objective 20

In summary, whenever an energy In summary, whenever an energy

change takes place in a closed system, change takes place in a closed system,

¾

¾the first law tells us the total energy the first law tells us the total energy

remains constant remains constant

h d l ll f

¾

¾the second law tells us free energy the second law tells us free energy

decreases. decreases.

How is this possible?How is this possible? ¾

¾entropy increases! So closed systems entropy increases! So closed systems

tend to become more disorganized. tend to become more disorganized.

Explain what a chemical

reaction is and discuss how

h

i l

i

d

h

i l

i

d

chemical equations are used to

describe the changes that take

place during a chemical reaction.

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Most of the changes that take place in Most of the changes that take place in

living organisms are the result of living organisms are the result of chemical reactions.

chemical reactions.

What is a chemical reaction?What is a chemical reaction? ¾

¾As atoms and molecules move around, As atoms and molecules move around,

they collide with each other. If they they collide with each other. If they collide with enough force, existing collide with enough force, existing chemical bonds can break and new chemical bonds can break and new bonds can form.

bonds can form. 13

Chemical equations can be used to Chemical equations can be used to

describe the changes that take place describe the changes that take place during a chemical reaction:

during a chemical reaction:

CH

₄₄

+ 2O

₂₂

CO

₂₂

+ 2H

₂₂

O

C

₄₄ ₂₂

C

₂₂ ₂₂

Reactants

Products

During a chemical reaction no atoms During a chemical reaction no atoms

are created or destroyed. are created or destroyed.

14

Most reactions are reversible:Most reactions are reversible: ¾

¾reading from left to right is called the reading from left to right is called the

forward reaction forward reaction

¾

¾reading from right to left is called the reading from right to left is called the ead g oead g o g t to e t s ca ed t eg t to e t s ca ed t e

reverse reaction reverse reaction

At At equilibriumequilibrium, the rate of the forward , the rate of the forward

reaction equals the rate of the reverse reaction equals the rate of the reverse reaction.

reaction.

15

Distinguish between endergonic

and exergonic reactions and

explain how they are coupled in

living organisms. Describe the

roles of ATP and ADP in the

coupling of chemical reactions.

16

Chemical reactions involve a

change in free energy as well as

a change in the types of

molecules present

molecules present.

All atoms and molecules have a certain All atoms and molecules have a certain

amount of free energy: amount of free energy:

¾

¾potential energy stored in the chemical potential energy stored in the chemical

bonds that hold them together. bonds that hold them together.gg

¾

¾kinetic energy due to their constant kinetic energy due to their constant

random motion. random motion.

Large, complex molecules have more Large, complex molecules have more

free energy than small molecules. free energy than small molecules.

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Exergonic reactionsExergonic reactions::

the reactants have more free energy the reactants have more free energy

than the products: than the products: C

C₆₆HH₁₂₁₂OO₆₆+ 6O+ 6O₂₂→ 6CO→ 6CO₂₂+ 6H+ 6H₂₂O O

ff ll ff

more free energy

more free energy less free energyless free energy

involve a net release of energy and/or involve a net release of energy and/or

an increase in entropy an increase in entropy

occur spontaneously (without a net occur spontaneously (without a net

input of energy) input of energy) 19 Objective 22 Objective 22

Endergonic reactionsEndergonic reactions::

the reactants have less free energy the reactants have less free energy

than the products: than the products:

6CO

6CO₂₂+ 6H+ 6H₂₂O → CO → C₆₆₆₆HH₁₂₁₂OO₆₆₆₆+ 6O+ 6O₂₂ less free energy

less free energy more free energymore free energy

involve a net input of energy and/or a involve a net input of energy and/or a

decrease in entropy decrease in entropy

do not occur spontaneouslydo not occur spontaneously

20 Product Energy must be supplied. E nergy supplied

Exergonic and Endergonic Reactions

21 Reactant Reactant Product Exergonic Endergonic Energy is released. E E n ergy rel eased

Living organisms have the ability to Living organisms have the ability to

couple

couple exergonic and endergonic exergonic and endergonic reactions:

reactions:

¾

¾energy released by exergonic reactions energy released by exergonic reactions gg gg

is captured and used to make ATP is captured and used to make ATP from ADP and Pi

from ADP and Pi

¾

¾ATP can be broken back down to ATP can be broken back down to

ADP and Pi, releasing energy to power ADP and Pi, releasing energy to power the cell’s endergonic reactions.

the cell’s endergonic reactions. 22

ATP ATP

Adenosine Adenosine triphosphatetriphosphate

The “energy currency” for all cellsThe “energy currency” for all cells

Composed ofComposed of

¾

¾Ribose Ribose –– 5 carbon sugar5 carbon sugar ¾

¾AdenineAdenine ¾

¾Chain of 3 phosphatesChain of 3 phosphates

Key to energy storageKey to energy storage

Bonds are unstableBonds are unstable

ADP ADP –– 2 phosphates2 phosphates

AMP AMP –– 1 phosphate 1 phosphate –– lowest energy formlowest energy form

Structure of ATP

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The ATP Cycle

25

Explain the concepts of

chemical equilibrium, transition

d

i

d

i

state, and activation energy.

26

All reactions, both endergonic and All reactions, both endergonic and

exergonic, require an input of energy to exergonic, require an input of energy to get started. This energy is called

get started. This energy is called activation energy

activation energy..

A i i i d d b i h

Activation energy is needed to bring the Activation energy is needed to bring the

reactants close together and weaken reactants close together and weaken existing bonds. This produces an existing bonds. This produces an unstable state of maximum potential unstable state of maximum potential energy called the

energy called the transition statetransition state..

27 Activation energy Energy supplied Transition State 28 Reactant Product E n erg y rel eased

Describe some methods that

can be used to speed up

p

chemical reactions.

In most cases, molecules do not have In most cases, molecules do not have

enough kinetic energy to reach the enough kinetic energy to reach the transition state when they collide. transition state when they collide.

Therefore, most collisions are nonTherefore, most collisions are

non--productive, and the reaction proceeds productive, and the reaction proceeds very slowly if at all.

very slowly if at all.

What can be done to speed up these What can be done to speed up these

reactions? reactions?

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1)

1) Add Heat Add Heat –– molecules move faster molecules move faster so they collide more frequently and so they collide more frequently and with greater force.

with greater force. 2)

2) Add a catalyst Add a catalyst –– a catalyst reduces a catalyst reduces the energy needed to reach the the energy needed to reach the activation state, without being activation state, without being changed itself. Proteins that function changed itself. Proteins that function as catalysts are called

as catalysts are called enzymesenzymes..

31 Activation energy Activation Energy supplied

Activation Energy and Catalysis

32 Reactant Product Catalyzed Uncatalyzed Product Reactant energy E n ergy rel eased

Unlike heat, which speeds up all Unlike heat, which speeds up all

reactions indiscriminately, enzymes are reactions indiscriminately, enzymes are highly specific. Each enzyme typically highly specific. Each enzyme typically speeds up only one or a few similar speeds up only one or a few similar chemical reactions.

chemical reactions.

Therefore, by controlling which Therefore, by controlling which

enzymes are made, a cell can control enzymes are made, a cell can control which reactions take place in the cell. which reactions take place in the cell.

33

Describe the structure,

function, and characteristics

,,

of enzymes.

Almost all enzymes are globular Almost all enzymes are globular

proteins with one or more pockets on proteins with one or more pockets on their surface called

their surface called active sitesactive sites..

Reactants bind to the active site to Reactants bind to the active site to

form an

form an enzymeenzyme--substrate complexsubstrate complex..

The 3The 3--D shape of the active site and D shape of the active site and

the substrates must match, like a lock the substrates must match, like a lock and key.

and key.

Binding of the substrates causes the Binding of the substrates causes the

enzyme to adjust its shape slightly, enzyme to adjust its shape slightly, leading to a better

leading to a better induced fitinduced fit..

When this happens, the substrates are When this happens, the substrates are pppp

brought close together and existing brought close together and existing bonds are stressed. This reduces the bonds are stressed. This reduces the amount of energy needed to reach the amount of energy needed to reach the transition state.

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37

Binding of the substrates causes the enzyme to adjust

its shape slightly, leading to a better induced fit. 38

39

Explain how the following factors Explain how the following factors can affect enzyme activity:

can affect enzyme activity: a) a) temperaturetemperature b) b) pHpH b) b) pHpH c)

c) inhibitors and activatorsinhibitors and activators d) d) cofactorscofactors 40 Objective 26 Objective 26

The rate of an enzymeThe rate of an enzyme--catalyzed catalyzed

reaction is affected by the reaction is affected by the

concentration of both the enzyme and concentration of both the enzyme and its substrates.

its substrates.

In addition, any physical or chemical In addition, any physical or chemical

factors that affect the enzyme’s 3 factors that affect the enzyme’s 3--D D shape can affect the enzyme’s ability to shape can affect the enzyme’s ability to catalyze the reaction

catalyze the reaction

41

Objective 26a & b Objective 26a & b

Temperature and pH:Temperature and pH: ¾

¾Most enzymes have an optimum Most enzymes have an optimum

temperature and an optimum pH. temperature and an optimum pH. These are related to the environment These are related to the environment where the enzyme normally functions. where the enzyme normally functions.

¾

¾Enzyme activity decreases above or Enzyme activity decreases above or

below the optimum. below the optimum.

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Optimum temperature for

human enzyme Optimum temperature for enzymefrom hotsprings prokaryote

o

f Reacti

o

n

Relationship of Enzyme Activity to Temperature

43

Temperature of Reaction (o_C)

Rate

o

30 40 50 60 70 80

Optimum pH for pepsin

e

acti

o

n

Optimum pH for trypsin

Relationship of Enzyme Activity to pH

44

Rate of R

e

1 2 3 4 5 6 7 8 9

Objective 26c Objective 26c

Inhibitors and activators are Inhibitors and activators are

substances that bind to an enzyme substances that bind to an enzyme and affect its ability to catalyze a and affect its ability to catalyze a reaction.

reaction.

ActivatorsActivators bind to a region of the bind to a region of the

enzyme called the

enzyme called the allosteric siteallosteric site, , thereby maintaining the enzyme’s thereby maintaining the enzyme’s active configuration and its activity. active configuration and its activity.

45

Objective 26c Objective 26c

Inhibitors decrease enzyme activity in Inhibitors decrease enzyme activity in

one of 2 ways: one of 2 ways: 1)

1)competitive inhibitorscompetitive inhibitors bind to the bind to the active site, thereby preventing the active site, thereby preventing the pp gg substrates from binding.

substrates from binding. 2)

2)noncompetitive inhibitorsnoncompetitive inhibitors bind to an bind to an allosteric site, thereby altering the allosteric site, thereby altering the shape of the active site so that it shape of the active site so that it cannot bind to the substrate.

cannot bind to the substrate. 46

Active site Substrate

Inhibitor

Noncompetitive inhibition When an inhibitor joins to an allosteric site and alters the shape of the active site so it cannot bind to the substrate, this is called…

Enzyme Allosteric site Substrate Inhibitor Active site

Competitive inhibition When an inhibitor binds to the active site of an enzyme and blocks the substrate from binding, this is called…

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Objective 26d Objective 26d

CofactorsCofactors are nonprotein substances are nonprotein substances

required by enzymes in order to required by enzymes in order to function. For example, the active site function. For example, the active site of many enzymes contain metal ions of many enzymes contain metal ions that help draw electrons away from the that help draw electrons away from the substrates.

substrates.

Organic molecules that function as Organic molecules that function as

cofactors are called

cofactors are called coenzymescoenzymes..

49

Define the terms “metabolism”

and “metabolic pathway” (or

“bi h

i l

h

”)

d

“bi h

i l

h

”)

d

“biochemical pathway”) and

explain how metabolic pathways

are regulated.

MetabolismMetabolism refers to the sum of all refers to the sum of all

chemical reactions carried out by an chemical reactions carried out by an organism:

organism:

¾

¾reactions that join small molecules reactions that join small molecules jj

together to form larger, more complex together to form larger, more complex molecules are called

molecules are called anabolicanabolic..

¾

¾reactions that break large molecules reactions that break large molecules

down into smaller subunits are called down into smaller subunits are called catabolic

catabolic.. 51

A sequence of chemical reactions, A sequence of chemical reactions,

where the product of one reaction where the product of one reaction serves as a substrate for the next, is serves as a substrate for the next, is called a

called a metabolic pathwaymetabolic pathway (or (or biochemical pathway

biochemical pathway).).

Most metabolic pathways take place in Most metabolic pathways take place in

specific regions of the cell. specific regions of the cell.

52

53

The regulation of simple metabolic The regulation of simple metabolic

pathways often depends on

pathways often depends on feedback feedback inhibition

inhibition::

¾

¾the end product of the pathway binds the end product of the pathway binds pp pp

to an allosteric site on the enzyme that to an allosteric site on the enzyme that catalyzes the first reaction and

catalyzes the first reaction and inactivates it.

inactivates it.

Why is the first reaction targeted?Why is the first reaction targeted?

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