Download ppt - Overview: The Energy of Life Living cell = miniature chemical factory where thousands of reactions occur Cell extracts energy applies it to perform

Overview: The Energy of Life

Living cell = miniature chemical factory where thousands of reactions occur

Cell extracts energy applies it to perform work Some organisms convert energy light,

bioluminescence

Concept 8.1: An organism’s metabolism transforms matter and energy, subject to

the laws of thermodynamics

Metabolism: totality of organism’s chemical reactions an emergent property of life that arises from interactions

between molecules within the cell

Organization of the Chemistry of Life into Metabolic Pathways

Metabolic pathway: begins with specific molecule and ends with a product Each step catalyzed by a specific enzyme

Catabolic pathways: release energy by breaking down complex molecules into simpler compounds Ex: Cellular respiration= the breakdown of glucose in the

presence of oxygen Anabolic pathways:

consume energy to build complex molecules from simpler ones Ex: synthesis of

protein from amino acids

Bioenergetics: study of how organisms manage their energy resources

Organization of the Chemistry of Life into Metabolic Pathways

Forms of Energy

Energy: the capacity to cause change exists in various forms, some can perform work

Kinetic energy: energy associated with motion

Heat (thermal energy): kinetic energy associated with random movement of atoms or molecules

Potential energy: energy that matter possesses because of its location or structure

Chemical energy: potential energy available for release in a chemical reaction

Energy can be converted from one form to another

Fig. 8-2

Climbing up converts the kineticenergy of muscle movementto potential energy.

A diver has less potentialenergy in the waterthan on the platform.

Diving convertspotential energy tokinetic energy.

A diver has more potentialenergy on the platformthan in the water.

The Laws of Energy Transformation

Thermodynamics: study of energy transformations

Closed system is isolated from its surroundings Ex: liquid in a thermos,

In open system energy and matter can be transferred between the system and its surroundings Ex: Organisms!

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The First Law of Thermodynamics

First law of thermodynamics: energy of the universe is constant: – Energy can be transferred and transformed, but it cannot be

created or destroyed

Also called the principle of conservation of energy

The Second Law of Thermodynamics

Second law of thermodynamics: during every energy transfer or transformation, some energy is unusable, and is often lost as heat Every energy transfer or transformation increases the

entropy (disorder) of the universe Living cells unavoidably

convert organized energy forms heat

Spontaneous processes occur without energy input quickly or slowly

For a process to occur without energy input, it must increase the entropy of universe

Fig. 8-3

(a) First law of thermodynamics (b) Second law of thermodynamics

Chemicalenergy

Heat CO2

H2O

+

Biological Order and Disorder

Cells create ordered structures from less ordered materials

Organisms replace ordered forms of matter and energy with less ordered forms

Energy: Flows into an ecosystem

as light and Exits as heat Explain this.

Evolution of more complex organisms does not violate the second law of thermodynamics Why not?

Entropy (disorder) may decrease in an organism, but the universe’s total entropy increases


Fig. 8-4

50 µm

Root of buttercup plant; As open system, plants can increase their order as long

as order of surroundings decrease

Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction

occurs spontaneously

Biologists want to know which reactions occur spontaneously and which require input of energy THUS! they need to

determine energy changes that occur in chemical reactions

Free-Energy Change, G

Free energy: energy that can do work when temperature and pressure are uniform like in a living cell

Change in free energy (∆G) during a process is related to change in enthalpy/change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T):

∆G = ∆H – T∆S• Only processes with a negative ∆G are spontaneous• Spontaneous processes can be harnessed to perform

work Can you think of one?


Free Energy, Stability, and Equilibrium Free energy is a measure of a system’s instability or its

tendency to change to a more stable state During spontaneous change:

free energy decreases stability of system increases

Equilibrium: state of maximum stability A process is spontaneous and can perform work only

when it is moving toward equilibrium

Fig. 8-5

(a) Gravitational motion (b) Diffusion (c) Chemical reaction

• More free energy (higher G)• Less stable• Greater work capacity

In a spontaneous change• The free energy of the system decreases (∆G < 0)• The system becomes more stable• The released free energy can be harnessed to do work

• Less free energy (lower G)• More stable• Less work capacity

Fig. 8-5a

• Less free energy (lower G)• More stable• Less work capacity

• More free energy (higher G)• Less stable• Greater work capacity

In a spontaneous change• The free energy of the system decreases (∆G < 0)• The system becomes more stable• The released free energy can be harnessed to do work

Fig. 8-5b

Spontaneouschange

Spontaneouschange

Spontaneouschange

(b) Diffusion (c) Chemical reaction(a) Gravitational motion

Free Energy and Metabolism

Concept of free energy can be applied to chemistry of life’s processes

Exergonic reaction: net release of free energy; spontaneous

Endergonic reaction: absorbs free energy from its surroundings; nonspontaneous

Fig. 8-6a

Energy

(a) Exergonic reaction: energy released

Progress of the reaction

Fre

e en

erg

y

Products

Amount ofenergy

released(∆G < 0)

Reactants

Fig. 8-6b

Energy

(b) Endergonic reaction: energy required


Fre

e en

erg

y

Products

Amount ofenergy

required(∆G > 0)

Reactants

Equilibrium and Metabolism

Reactions in closed system eventually reach equilibrium and then do no work

Cells not in equilibrium; they are open systems with constant flow of materials

Defining feature of life = metabolism is never at equilibrium

Catabolic pathway: releases free energy in a series of reactions


Fig. 8-7

(a) An isolated hydroelectric system

∆G < 0 ∆G = 0

(b) An open hydroelectric system ∆G < 0

∆G < 0

∆G < 0

∆G < 0

(c) A multistep open hydroelectric system

Fig. 8-7a

(a) An isolated hydroelectric system

∆G < 0 ∆G = 0

Fig. 8-7b

(b) An open hydroelectric system

∆G < 0

Fig. 8-7c

(c) A multistep open hydroelectric system

∆G < 0

∆G < 0

∆G < 0

Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic

reactions

Cell does three main kinds of work: Chemical Transport Mechanical

Cells manage energy resources by energy coupling the use of an

exergonic process to drive an endergonic one

Most energy coupling in cells mediated by ATPCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Structure and Hydrolysis of ATP

ATP (adenosine triphosphate): cell’s energy shuttle

ATP is composed of : ribose (a sugar) adenine (a nitrogenous base) three phosphate groups

Bonds between phosphate groups of ATP’s tail can be broken by hydrolysis

Energy released from ATP when terminal phosphate bond broken comes from chemical change

to a state of lower free energy, not from the phosphate bonds themselves

How ATP Performs Work Three types of cellular work (mechanical, transport, and

chemical) powered by the hydrolysis of ATP In cell energy from exergonic reaction of ATP hydrolysis

can be used to drive a endergonicreaction

Overall: coupled reactions are exergonic

ATP drives endergonic reactions by phosphorylation transferring a

phosphate group to some other molecule, such as a reactant

recipient molecule is now phosphorylated

Fig. 8-10

(b) Coupled with ATP hydrolysis, an exergonic reaction

Ammonia displacesthe phosphate group,forming glutamine.

(a) Endergonic reaction

(c) Overall free-energy change

PP

GluNH3

NH2

Glu i

GluADP+

PATP+

+

Glu

ATP phosphorylatesglutamic acid,making the aminoacid less stable.

GluNH3

NH2

Glu+

Glutamicacid

GlutamineAmmonia

∆G = +3.4 kcal/mol

+2

1

The Regeneration of ATP ATP renewable resource that is regenerated by addition

of phosphate group to adenosine diphosphate (ADP) Energy to phosphorylate ADP comes from catabolic

reactions in the cell Chemical potential energy temporarily stored in ATP

drives most cellular work


Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers

Catalyst: chemical agent that speeds up a reaction without being consumed by the reaction

Enzyme: catalytic protein

Enzyme-catalyzed reaction Ex: Hydrolysis of

sucrose by enzyme sucrase


The Activation Energy Barrier

Every chemical reaction between molecules involves bond breaking AND bond forming

Free energy of activation, or activation energy (EA): initial energy needed to start chemical reaction often supplied in

form of heat from the surroundings

How Enzymes Lower the EA Barrier

Enzymes catalyze reactions by lowering EA barrier Enzymes do not affect change in free energy (∆G);

instead, they hasten reactions that would occur eventually

Substrate Specificity of Enzymes

Substrate: reactant that an enzyme acts on Enzyme-substrate complex: formed when enzyme

binds to its substrate Active site: region on the enzyme where the substrate

binds Induced fit of substrate brings chemical groups of active

site into positions that enhance their ability to catalyze the reaction

Catalysis in the Enzyme’s Active Site

In enzymatic reaction the substrate binds to the active site of the enzyme

Active site can lower an EA barrier by Orienting substrates

correctly Straining substrate bonds Providing a favorable

microenvironment Covalently bonding to the

substrate

Fig. 8-17

Substrates

Enzyme

Products arereleased.

Products

Substrates areconverted toproducts.

Active site can lower EA

and speed up a reaction.

Substrates held in active site by weakinteractions, such as hydrogen bonds andionic bonds.

Substrates enter active site; enzyme changes shape such that its active siteenfolds the substrates (induced fit).

Activesite is

availablefor two new

substratemolecules.

Enzyme-substratecomplex

5

3

21

6

4

Effects of Local Conditions on Enzyme Activity

Enzyme’s activity can be affected by General

environmental factors Temperatur

e pH

Chemicals that specifically influence enzyme

Fig. 8-18

Ra

te o

f re

ac

tio

n

Optimal temperature forenzyme of thermophilic

(heat-tolerant) bacteria

Optimal temperature fortypical human enzyme

(a) Optimal temperature for two enzymes

(b) Optimal pH for two enzymes

Ra

te o

f re

ac

tio

n

Optimal pH for pepsin(stomach enzyme)

Optimal pHfor trypsin(intestinalenzyme)

Temperature (ºC)

pH543210 6 7 8 9 10

0 20 40 80 60 100

Cofactors Cofactors: nonprotein enzyme helpers

may be inorganic (such as a metal in ionic form) or organic

Coenzyme: organic cofactor include vitamins


Enzyme Inhibitors Competitive inhibitors: bind to active site of enzyme,

competing with the substrate

Noncompetitive inhibitors: bind to another part of enzyme, causing enzyme to change shape and making active site less effective

Examples: toxins, poisons, pesticides, and antibiotics

Fig. 8-19

(a) Normal binding (c) Noncompetitive inhibition(b) Competitive inhibition

Noncompetitive inhibitor

Active siteCompetitive inhibitor

Substrate

Enzyme

Concept 8.5: Regulation of enzyme activity helps control metabolism

Chemical chaos would result if cell’s metabolic pathways were not tightly regulated

Cell does this by: 1. switching on/off genes that encode specific enzymes

2. regulating the activity of enzymes


Allosteric Regulation of Enzymes

Allosteric regulation may either inhibit or stimulate an enzyme’s activity occurs when a regulatory molecule binds to protein at

one site and affects the protein’s function at another site

Allosteric Activation and

Inhibition Most allosterically regulated enzymes

made from polypeptide subunits Each enzyme has active and inactive

forms Binding of activator stabilizes the

active form of the enzyme Binding of inhibitor stabilizes the

inactive form of the enzyme Cooperativity: form of allosteric

regulation that can amplify enzyme activity binding by substrate to one active

site stabilizes favorable conformational changes at all other subunits

Fig. 8-20a

(a) Allosteric activators and inhibitors

InhibitorNon-functionalactivesite

Stabilized inactiveform

Inactive form

Oscillation

Activator

Active form Stabilized active form

Regulatorysite (oneof four)

Allosteric enzymewith four subunits

Active site(one of four)

Fig. 8-20b

(b) Cooperativity: another type of allosteric activation

Stabilized activeform

Substrate

Inactive form

Identification of Allosteric Regulators

Allosteric regulators = attractive drug candidates for enzyme regulation

Inhibition of proteolytic enzymes called caspases may help management of inappropriate inflammatory responses

Fig. 8-21a

SH

Substrate

Hypothesis: allostericinhibitor locks enzymein inactive form

Active form canbind substrate

S–SSH

SH

Activesite

Caspase 1

Known active form

Known inactive form

Allostericbinding site

Allostericinhibitor

EXPERIMENT

Fig. 8-21b

Caspase 1

RESULTS

Active form

Inhibitor

Allostericallyinhibited form

Inactive form

Feedback Inhibition

Feedback inhibition: end product of a metabolic pathway shuts down the pathway Prevents cell

from wasting chemical resources by synthesizing more product than needed

Specific Localization of Enzymes Within the Cell

Structures within cell help bring order to metabolic pathways

Some enzymes act as structural components of membranes

In eukaryotic cells, some enzymes reside in specific organelles Ex: enzymes for

cellular respiration located in mitochondria


You should now be able to:

1. Distinguish between the following pairs of terms: 1. catabolic and anabolic pathways2. kinetic and potential energy3. open and closed systems 4. exergonic and endergonic reactions

2. In your own words, explain the second law of thermodynamics and explain why it is not violated by living organisms

3. Explain in general terms how cells obtain the energy to do cellular work

4. Explain how ATP performs cellular work 5. Explain why an investment of activation energy is

necessary to initiate a spontaneous reaction6. Describe the mechanisms by which enzymes lower

activation energy7. Describe how allosteric regulators may inhibit or

stimulate the activity of an enzyme

Fig. 8-UN2


Products

Reactants

∆G is unaffectedby enzyme

Course ofreactionwithoutenzyme

Fre

e en

erg

y

EA

withoutenzyme EA with

enzymeis lower

Course ofreactionwith enzyme