Chapter 6 ppt

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Biology

Sylvia S. Mader Michael Windelspecht

Chapter 6 Metabolism:

Energy and

Enzymes

Lecture Outline

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Outline

• 6.1 Cells and the Flow of Energy

• 6.2 Metabolic Reactions and Energy

Transformations

• 6.3 Metabolic Pathways and Enzymes

• 6.4 Organelles and the Flow of Energy

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6.1 Cells and the Flow of

Energy

• Energy

– The ability to do work or bring

about a change



Kinetic energy

• Energy of motion

• Mechanical



Potential energy

• Stored energy

• Chemical energy

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Flow of Energy

4

solar energy

heat

Mechanical energy Chemical

energy

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Two Laws of

Thermodynamics

• First law:

 Law of conservation of energy

 Energy cannot be created or destroyed, but can be

changed from one form to another

• Second law:

 Law of entropy

 When energy is changed from one form to another,

there is a loss of usable energy

 Waste energy goes to increase disorder

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sun

CO₂

H₂O

solar energy producer

carbohydrate heat

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Carbohydrate Metabolism

carbohydrate uncontracted muscle contracted muscle

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Cells and Entropy

H+

H₂O

C₆H₁₂O₆

• more organized • more potential energy • less stable (entropy) a.

Carbon dioxide and water • less organized • less potential energy • more stable (entropy)

CO₂ kinetic energy channel protein H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Unequal distribution of hydrogen ions

Equal distribution of hydrogen ions • more organized

• more potential energy

b.

• less stable (entropy)

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6.2 Metabolic Reactions and Energy

Transformations

• Metabolism

 Sum of cellular chemical reactions in cell

 Reactants participate in a reaction

 Products form as result of a reaction

• Free energy

is the amount of energy available

to perform work

 Exergonic Reactions - Products have less free energy than reactants (release energy)

 Endergonic Reactions - Products have more free energy than reactants (require energy input)

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ATP: Energy for Cells

• Adenosine triphosphate (ATP)



High energy compound used to drive metabolic

reactions



Constantly being generated from

adenosine

diphosphate (ADP)

• Composed of:



Adenine, ribose (together = adenosine), and three

phosphate groups

• Coupled reactions



Energy released by an exergonic reaction

captured in ATP



ATP is used to drive an endergonic reaction

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The ATP Cycle

P

adenosine triphosphate

ATP is unstable and has

a high potential energy.

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The ATP Cycle

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P P P

P

adenosine triphosphate ATP is unstable and has a high potential energy.

ATP

Endergonic Reaction:

• The hydrolysis of ATP releases previously stored energy, allowing the change in free energy to do work and drive other processes. • Has negative delta G.

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The ATP Cycle

P P + P P P P

+ P

ATP

• The hydrolysis of ATP releases Previously stored energy, allowing the change in free energy to do work and drive other processes. • Has negative delta G.

• Examples: protein synthesis, nerve conduction, muscle contraction

adenosine diphosphate phosphate

ADP is more stable and has lower potential energy than ATP. +

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The ATP Cycle

14

P P + P P P P

+ + P

Exergonic Reaction: • Creation of ATP from ADP and Prequires input of energy from Other sources. • Has positive delta G. • Example: cellular respiration

ATP

ADP

adenosine diphosphate phosphate ADP is more stable and has lower potential energy than ATP.

• The hydrolysis of ATP releases Previously stored energy, allowing the change in free energy to do work and drive other processes. • Has negative delta G.

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Coupled Reactions

15

1 Myosin assumes its resting shape when It combines with ATP.

myosin actin

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Coupled Reactions

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1 ₂

P Myosin assumes its

resting shape when It combines with ATP.

ATP splits into ADP and p , causing myosin to change its shape and allowing it to attach to actin.

ADP myosin

actin

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Coupled Reactions

1 2 3

Release of ADP and p cause myosin to again change shape and pull again stactin, generating force and motion.

ADP myosin

actin

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Coupled Reactions

1 2 3

Release of ADP and p cause myosin to again change shape and pull against actin, generating force and motion.

ADP myosin

actin

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6.3 Metabolic Pathways and

Enzymes

• Reactions usually occur in a sequence

 Products of an earlier reaction become reactants of a

later reaction

 Such linked reactions form a metabolic pathway

• Begins with a particular reactant, proceeds through several intermediates, and terminates with a particular end product

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A



B



C



D



E



F



G

“A” is Initial Reactant

“G” is End

Product B, C, D, E, and F

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6.3 Metabolic Pathways and

Enzymes

• Enzyme

 Protein molecules that function as catalysts

 The reactants of an enzymatically catalyzed reaction

are called substrates

 Each enzyme accelerates a specific reaction

 Each reaction in a metabolic pathway requires a

unique and specific enzyme

 The end product will not be formed unless ALL

enzymes in the pathway are present and functional

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Energy of Activation

• Molecules frequently do not react with one

another unless they are activated in some way

 Energy must be added to at least one reactant to

initiate the reaction

• Energy of activation

• Enzyme Operation:

 Enzymes operate by lowering the energy of

activation

 Accomplished by bringing substrates into contact with

one another

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Energy of Activation

22

Progress of the Reaction energy of

reactant

energy of product

energy of activation (Ea)

enzyme not present

enzyme present

Fre

e

E

ner

gy

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Enzyme-Substrate Complex

• The

active site

complexes with the

substrates



Causes the active site to change shape



Shape change forces substrates together,

initiating bond



Induced fit model

• Enzyme is induced to undergo a slight alteration to

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Enzyme-Substrate Complex

• Degradation:

 Enzyme complexes with a single substrate molecule

 Substrate is broken apart into two product molecules

• Synthesis:

 Enzyme complexes with two substrate molecules

 Substrates are joined together and released as a

single product molecule

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Enzymatic Actions

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Degradation

The substrate is broken down to smaller products. products substrate enzyme a. b. active site enzyme-substrate complex enzyme Synthesis

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Factors Affecting Enzymatic

Speed

• Substrate concentration

 Enzyme activity increases with substrate

concentration due to more frequent collisions between substrate molecules and the enzyme

• Temperature

 Enzyme activity increases with temperature

 Warmer temperatures cause more effective collisions

between enzyme and substrate

 However, hot temperatures can denature and

destroy enzymes

• pH

 Most enzymes are optimized for a particular pH

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The Effect of Temperature on Rate of

Reaction

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Rat e o f Rea c tio n (p ro d u c t p e r u n it o f tim e )

0 10 20 30 40 50 60

a. Rate of reaction as a function of temperature

b. Body temperature of ectothermic animals often limits rates of reactions.

c. Body temperature of endothermic animals promotes rates of reactions.

Temperature C

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The Effect of pH on Rate of Reaction

28

Rate

of

Reac

ti

on

(produc

t

pe

r un

it o

f

ti

m

e)

pH

0 1 2 3 4 5 6 7 8 9 10 11 12

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Factors Affecting Enzymatic

Speed

• Cells can regulate the presence/absence of an

enzyme

• Cells can regulate the concentration of an

enzyme

• Cells can activate or deactivate some enzymes

 Enzyme Cofactors

• Molecules required to activate enzyme

• Coenzymes are nonprotein organic molecules

• Vitamins are small organic compounds required in the diet

for the synthesis of coenzymes

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Cofactors at Active Site

30

cofactor

active site

a.

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Cofactors at Active Site

substrate

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Cofactors at Active Site

cofactor

active

site substrate

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Enzyme Inhibition

• Reversible enzyme inhibition



A substance known as an inhibitor binds to an

enzyme and decreases its activity

• Competitive inhibition – the substrate and the

inhibitor are both able to bind to active site

• Noncompetitive inhibition – the inhibitor does not

bind at the active site, but at an allosteric site

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Noncompetitive Inhibition of an Enzyme

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2 active site enzymes substrates allosteric site E

2 E3 E4 E5

A A F (end product) A

Metabolic pathway produces F, the end product.

F binds to allosteric site and the active site of E1 changes shape.

A cannot bind to E1; the enzyme has been inhibited by F.

B C D E

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Enzyme Inhibitors Can Spell

Death

• Materials that irreversibly inhibit an enzyme are

known as poisons

• Cyanide inhibits enzymes required for ATP

production

• Sarin inhibits an enzyme located at the

neuromuscular junction.

• Warfarin inhibits an enzyme responsible for the

blood clotting process

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6.4 Organelles and the Flow

of Energy

• Oxidation-reduction (redox) reactions



Electrons pass from one molecule to another

• Oxidation - loss of an electron

• Reduction – gain of an electron



Both take place at same time



One molecule accepts the electron given up by

the other

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Photosynthesis and Cellular Respiration

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Electron Transport Chain

• Consists of membrane-bound carrier proteins

found in mitochondria and chloroplasts

• Physically arranged in an ordered series

 Starts with high-energy electrons

 Pass electrons from one carrier to another

• Electron energy used to pump hydrogen ions (H+_{) to one side}

of membrane

• Establishes an electrochemical gradient across the membrane

• The electrochemical gradient is used to make ATP from ADP

– Chemiosmosis

 Ends with low-energy electrons and high-energy ATP

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ElectronTransport Chain

e–

high-energy electrons

High-energy electrons are unstable and have high potential energy. This energy is released in stages, as kinetic energy, during the

electron transport chain.

electron transport chain

low-energy electrons As energy is released,

the electrons become more stable and have less potential energy.

ATP energy for

Synthesis of

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Chemiosmosis

High H+ _{concentration}

H+ _{pump in electron}

transport chain

H+

Low H+ _{concentration}

NADH _{NAD +}

H+

ATP

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Chemiosmosis

transport chain H+

H+

NADH _{NAD +}

ATP

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Chemiosmosis

H+

NADH _{NAD +}

ATP

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Chemiosmosis

P

H+

NADH _{NAD +}

ATP

synthase complex ATP

ADP +