Chapter8Metabolism.ppt

CHAPTER 8

WHAT YOU NEED TO KNOW:

 The key role of ATP in energy coupling.

 That enzymes work by lowering the energy of activation.

 The catalytic cycle of an enzyme that results in the production of a final

product.

CONCEPT 8.1: AN ORGANISM’S METABOLISM

TRANSFORMS MATTER AND ENERGY, SUBJECT TO THE LAWS OF THERMODYNAMICS

 Metabolism is the totality of an organism’s

chemical reactions

 Metabolism is an emergent property of life that arises from interactions between molecules

 Kinetic energy is energy associated with motion

 Heat (thermal energy) is kinetic energy associated

with random movement of atoms or molecules

 Potential energy is energy that matter possesses because

of its location or structure

 Chemical energy is potential energy available for

release in a chemical reaction

 Energy can be converted from one form to another  (i.e. chemical to mechanical or electrical)

LE 8-2

On the platform, the diver has more potential energy.

Diving converts potential

energy to kinetic energy.

Climbing up converts kinetic energy of muscle movement to potential energy.

THE LAWS OF ENERGY

TRANSFORMATION

 Thermodynamics is the study of energy transformations

 A closed system, such as that approximated by liquid in a thermos, is isolated from its

surroundings

 In an open system, energy and matter can be transferred between the system and its

surroundings

THE FIRST LAW OF

THERMODYNAMICS

 According to the first law of thermodynamics, the energy of the universe is constant

 Energy can be transferred and transformed

 Energy cannot be created or destroyed

 The first law is also called the principle of

 Catabolic pathways release energy by breaking down complex molecules into simpler compounds  C₆H₁₂O₆ +6O₂ 6H₂O + 6CO₂ +E

 Anabolic pathways consume energy to build complex molecules from simpler ones

THE SECOND LAW OF

THERMODYNAMICS

 During every energy transfer or transformation,

some energy is unusable, often lost as heat

 According to the second law of thermodynamics, every energy transfer or transformation

LE 8-3

Chemical

energy Heat

CO2

First law of thermodynamics Second law of thermodynamics

CONCEPT 8.3 ATP POWERS CELLULAR WORK BY COUPLING EXERGONIC REACTIONS TO

ENDERGONIC REACTIONS

 A cell does three main kinds of work:

 Mechanical

 Transport

 Chemical

 To do work, cells manage energy resources by energy coupling, the use of an

exergonic (energy releasing) process to drive an

THE STRUCTURE AND HYDROLYSIS

OF ATP

 ATP (adenosine triphosphate) is the cell’s energy shuttle

 ATP provides energy for cellular functions

Phosphat

e groups Adenine

 The bonds between the phosphate groups of ATP’s

tail can be broken by hydrolysis

 Energy is released from ATP when the terminal

phosphate bond is broken

 This release of energy comes from the chemical

LE 8-9

Adenosine triphosphate (ATP)

Energy P P P

P P

P_i

Adenosine diphosphate (ADP) Inorganic phosphate

H2O

LE 8-12

P i ADP

Energy for cellular work (endergonic, energy-consuming processes) Energy from catabolism

(energonic, energy-yielding processes)

ATP

HOW ATP PERFORMS WORK

 ATP drives endergonic reactions by

phosphorylation, transferring a phosphate group to some other molecule, such as a reactant

 The recipient molecule is now phosphorylated

LE 8-11 NH₂ Glu P_i P_i P_i P_i

Glu NH3

P

P P

ATP ADP

Motor protein

Mechanical work: ATP phosphorylates motor proteins Protein moved

Membrane protein

Solute

Transport work: ATP phosphorylates transport proteins Solute transported

Chemical work: ATP phosphorylates key reactants Reactants: Glutamic acid

and ammonia Product (glutamine)made

+ +

CONCEPT 8.4: ENZYMES SPEED UP

METABOLIC REACTIONS BY LOWERING ENERGY BARRIERS

 A catalyst is a chemical agent that speeds up a

reaction without being consumed by the reaction

 An enzyme is a catalytic protein

 Hydrolysis of sucrose by the enzyme sucrase is an

SUBSTRATE SPECIFICITY OF

ENZYMES

 The reactant that an enzyme acts on is called the enzyme’s substrate

 The enzyme binds to its substrate, forming an

enzyme-substrate complex

LE 8-17 Enzyme-substrate complex Substrates Enzyme Products

Substrates enter active site; enzyme changes shape so its active site

embraces the substrates (induced fit). Substrates held inactive site by weak interactions, such as hydrogen bonds and ionic bonds.

Active site (and R groups of its 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,

LE 8-15

Course of reaction without

enzyme E_without A enzyme

Progress of the reaction

F re e en er gy

EA with

 An enzyme’s activity can be affected by:

 General

environmental factors, such as temperature and pH

 Chemicals that

specifically influence the enzyme

Optimal temperature for

typical human enzyme Optimal temperature forenzyme of thermophilic

(heat-tolerant bacteria)

Temperature (°C)

Optimal temperature for two enzymes

R

at

e of

r

ea

ctio

n

Optimal pH for pepsin

(stomach enzyme) Optimal pH_{for trypsin}

(intestinal enzyme)

pH

Optimal pH for two enzymes

COFACTORS

 Cofactors are nonprotein enzyme helpers such as

minerals

 Coenzymes are organic cofactors such as vitamins

Enzyme Inhibitors

Competitive inhibitors bind to the active site of an enzyme, competing with the substrate

LE 8-19 Substrate Active site Enzyme Competitive inhibitor Normal binding Competitive inhibition Noncompetitive inhibitor Noncompetitive inhibition

A substrate can bind normally to the active site of an enzyme.

A competitive

inhibitor mimics the substrate, competing for the active site.

A noncompetitive

CONCEPT 8.5: REGULATION OF ENZYME ACTIVITY HELPS CONTROL METABOLISM

 Chemical chaos would result if a cell’s metabolic

pathways were not tightly regulated

 To regulate metabolic pathways, the cell switches

on or off the genes that encode specific enzymes

Allosteric Regulation of Enzymes

 a protein’s function at one site is affected by binding of a

regulatory molecule at another site

LE 8-20B

Substrate

Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation.

Cooperativity another type of allosteric activation

FEEDBACK INHIBITION

 In feedback inhibition, the end product of a metabolic pathway shuts down the pathway

LE 8-21 Active site available Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Enzyme 2 Intermediate A Isoleucine

used up by cell

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