Big Idea 2: Cellular Processes in Biological systems

EnergyGrowth

ReproductionDynamic Homeostasis

Learning Objectives:

LO 2.1 The student is able to explain how biological systems use free energy based on empirical data that all organisms require constant energy input to maintain organization, to grow and to reproduce.

Learning Objectives:

LO 2.2 The student is able to justify a scientific claim that free energy is required for living systems to maintain organization, to grow or to reproduce, but that multiple strategies exist in different living systems.

Learning Objectives:

LO 2.3 The student is able to predict how changes in free energy availability affect organisms, populations and ecosystems.

Enduring understanding 2.A:

Growth, reproduction and maintenance of the

organization of living systems require free energy and

matter.

Energy

Energy is the capacity to do work or ability to cause change. Any change in the universe requires energy. Energy comes in 2 forms:

–Potential energy is stored energy. No change is currently taking place

–Kinetic energy causes change. This always involves some type of motion.

1st Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant; it only changes from one form to another.

2nd Law of Thermodynamics: “In all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." This is also commonly referred to as entropy.

Entropy

It is a measure of disorder: cells are NOT disordered and so have low entropy. In the process of energy transfer, some energy will dissipate as heat.The flow of energy maintains order and life. Entropy wins when organisms cease to take in energy and die.

Biological systems follow the laws of thermodynamics, and to offset entropy, energy input must exceed energy lost from and used by

an organism to maintain order.

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Carbohydrate Metabolism

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carbohydratemuscle contraction

heat

Not only can energy deficiencies be detrimental to individual organisms, but changes in free energy availability also can affect population size and cause disruptions at the ecosystem level.

Organisms use various energy-related strategies to survive; strategies include different metabolic rates, physiological changes, and variations in reproductive and offspring-raising strategies.

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Cells and Energy

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H2O

CO2

energy

a.

•more organized

• more potential energy• less stable

Glucose

• less organized• less potential energy• more stable

Carbon dioxide and water

low entropyhigh entropy

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channel proteinenergy

b.

Unequal distribution of hydrogen ions

• more organized• more potential energy

• less stable

Equal distribution of hydrogen ions

• less organized• less potential energy• more stable

H+H

+ H+

H+

H +H+

H+H+

H+H+

H+H+

H+

H

+H

+

H+

H+

H+ H

low entropy high entropy

All living systems require constant input offree energy

a) Life requires a highly ordered system.1. Order is maintained by constant free energy input into the system.2. Loss of order or free energy flow results in death.3. Increased disorder and entropy are offset by biological processes that maintain or increase order.

The First Law of Thermodynamics– Energy cannot be created or destroyed– Energy can be transferred and transformed

For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement

Chemicalenergy

Free Energy:It is the portion of a system’s energy that is able to perform work when temperature and pressure is uniform throughout the system, as in a living cell• Free energy also refers to the amount of

energy actually available to break and subsequently form other chemical bonds

Free Energy:Gibbs’ free energy (G): in a cell, the amount of energy contained in a molecule’s chemical bonds Δ = changeG = free energyChange in free energy= ΔG and it is calculated as:energy left in products – energy content of reactants

-ΔG = products have less energy than reactants, and the reaction will occur spontaneously.+ΔG = products have more energy than the reactants, and the reaction will occur only if there is a constant input of energy

Free Energy:-ΔG reactions are exergonic (free energy releasing reactions)

+ΔG reactions are reactions that requires an input of free energy

Exergonic reactions (G < 0) or

Endergonic reactions (G > 0) on the basis of whether the free energy of the system

decreases or increases during the reaction.

Gibbs Free Energy

http://www.youtube.com/watch?v=DPjMPeU5OeM

Example 1:

Example 2

Find the change is Gibbs Free Energy for the reaction at 310C:HCl(aq) + NaOH(aq) H2O(l) + NaCl

Exergonic reactions (G < 0)

or Endergonic reactions

(G > 0)

Calculate ΔH° and ΔS° for the following reaction: NH4NO3(s)  + H2O(l)    NH4

+ (aq) + NO3- (aq)

b) Living systems do not violate the second law of thermodynamics, which states that entropy increases over time.1. Order is maintained by coupling cellular processes that increase entropy (and so have negative changes in free energy) with those that decrease entropy (and so have positive changes in free energy).2. Energy input must exceed free energy lost to entropy to maintain order and power cellular processes.3. Energetically favorable exergonic reactions, such as ATP→ADP, that have a negative change in free energy can be used to maintain or increase order in a system by being coupled with reactions that have a positive free energy change.

Exergonic reactions• Reactants have more free energy than the products • Involve a net release of energy and/or an increase in entropy• Occur spontaneously (without a net input of energy)

Reactants

Products

Energy

Progress of the reaction

Amount ofenergyreleased (∆G <0)

Fre

e e

ne

rgy

(a) Exergonic reaction: energy released

Endergonic Reactions• Reactants have less free energy than the products• Involve a net input of energy and/or a decrease in

entropy• Do not occur spontaneously

Energy

Products

Amount ofenergyreleased (∆G>0)

Reactants

Progress of the reaction

Fre

e e

ne

rgy

(b) Endergonic reaction: energy required

Reactant Reactant

Product

Product

ExergonicEndergonic

En

erg

y s

up

plie

d

En

erg

y r

ele

as

ed

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Metabolic Reactions and Energy Transformations

Metabolism:– Sum of cellular chemical reactions in cell

– Reactants participate in reaction

– Products form as result of reaction

Free energy is the amount of energy available to perform work

– Exergonic Reactions - Products have less free energy than reactants

– Endergonic Reactions - Products have more free energy than reactants

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ATP and Coupled Reactions

Adenosine triphosphate (ATP)– High energy compound used to drive metabolic

reactions– Constantly being generated from adenosine

diphosphate (ADP)Composed of:

– Adenine and ribose (adenosine), and– Three phosphate groups

Coupled reactions– Energy released by an exergonic reaction captured in

ATP– That ATP used to drive an endergonic reaction

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a.

b.

adenosine triphosphate

Energy from exergonic reactions(e.g., cellular respiration)

P

adenosine diphosphate

inorganic phosphate+P

Energy for endergonic reactions (e.g., protein synthesis, nerveconduction, muscle contraction)

P

P

P

ATP

P

Synthesis of ATP

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Work-Related Functions of ATP:

Primarily to perform cellular work– Chemical Work: Energy needed to synthesize

macromolecules– Transport Work: Energy needed to pump

substances across plasma membrane– Mechanical Work: Energy needed to contract

muscles, beat flagella, etc.

Life Requires Energy

http://www.youtube.com/watch?v=JBmykor-2kU

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Metabolic PathwaysReactions are usually occur in a sequence

Products of an earlier reaction become reactants of a later reaction

• Begins with a particular reactant• Proceeds through several intermediates• Terminates with a particular end product

AB C D E FG

“A” is Initial

Reactant

“G” is End

ProductB, C, D, E, and F

are Intermediates

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c) Energy-related pathways in biological systems are sequential and may be entered at multiple

points in the pathway.

Krebs cycle Glycolysis Calvin cycle Fermentation

Biological Order and Disorder

• Cells create ordered structures from less ordered materials

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

• The evolution of more complex organisms does not violate the second law of thermodynamics

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

Biological Order and Disorder

• Living systems– Increase the entropy of the universe– Use energy to maintain order– A living system’s free energy is energy that can do

work under cellular conditions– Organisms live at the expense of free energy

50µm

Metabolism: Part 1

http://www.youtube.com/watch?v=MUtfF2qnzGo

Equilibrium and Metabolism• Reactions in a closed system eventually reach

equilibrium and then do no work• Cells are not in equilibrium; they are open systems

experiencing a constant flow of materials

Equilibrium and Metabolism• A catabolic pathway in a cell releases free energy in

a series of reactions

Equilibrium and Metabolism• Closed and open hydroelectric systems can serve as

analogies

Equilibrium and Metabolism• Closed and open hydroelectric systems can serve as

analogies

(b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium.

∆G < 0

(c) A multistep open hydroelectric system. Cellular respiration is analogous to this system:

Glucose is broken down in a series of exergonic reactions that power the work of the cell.

The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium.

Equilibrium and MetabolismCells in our body experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium

Energy Coupling

• Living organisms have the ability to couple exergonic and endergonic reactions:

• Energy released by exergonic reactions is captured and used to make ATP from ADP and Pi

• ATP can be broken back down to ADP and Pi, releasing energy to power the cell’s endergonic reactions.

The Structure and Hydrolysis of ATP• ATP (adenosine triphosphate)

– Is the cell’s energy shuttle– Provides energy for cellular functions

O O O O CH2

H

OH OH

H

N

H H

O

NC

HC

N CC

N

NH2Adenine

RibosePhosphate groups

O

O O

O

O

O

-- - -

CH

The Structure and Hydrolysis of ATPEnergy is released from ATP when the terminal phosphate

bond is broken

P

Adenosine triphosphate (ATP)

H2O

+ Energy

Inorganic phosphate Adenosine diphosphate (ADP)

PP

P PP i

Cellular Work

• A cell does three main kinds of work– Mechanical– Transport– Chemical

• Energy coupling is a key feature in the way cells manage their energy resources to do this work

• ATP powers cellular work by coupling exergonic reactions to endergonic reactions

Energy Coupling - ATP / ADP Cycle• Releasing the third phosphate from ATP to make ADP generates energy

(exergonic):• Linking the phosphates together requires energy - so making ATP from ADP

and a third phosphate requires energy (endergonic), • Catabolic pathways drive the regeneration of ATP from ADP and phosphate

ATP synthesis from ADP + P i requires energy

ATP

ADP + P i

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

Energy from catabolism(exergonic, energy yieldingprocesses)

ATP hydrolysis to ADP + P i yields energy

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• The three types of cellular work (mechanical,

transport, and chemical) are powered by the hydrolysis of ATP

ATP drives endergonic reactions by phosphorylation, transferring a phosphate to other molecules - hydrolysis of

ATP: mechanical

ATP drives endergonic reactions by phosphorylation, transferring a phosphate to other molecules - hydrolysis of

ATP: transport

ATP drives endergonic reactions by phosphorylation, transferring a phosphate to other molecules - hydrolysis of

ATP: chemical

Activation Energy

• All reactions, both endergonic and exergonic, require an input of energy to get started. This energy is called activation energy

• The activation energy, EA

– Is the initial amount of energy needed to start a chemical reaction– Activation energy is needed to bring the reactants close together and

weaken existing bonds to initiate a chemical reaction. – Is often supplied in the form of heat from the surroundings in a system.

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Fre

e e

ne

rgy

Progress of the reaction

∆G < O

EAA B

C D

Reactants

A

C D

B

Transition state

A B

C D

Products

Reaction Rates

• In most cases, molecules do not have enough kinetic energy to reach the transition state when they collide.

• Therefore, most collisions are non-productive, and the reaction proceeds very slowly if at all.

• What can be done to speed up these reactions?

Increasing Reaction Rates• Add Energy (Heat) - molecules move faster so they collide more

frequently and with greater force.

Increasing Reaction Rates• Add a catalyst – a catalyst reduces the energy needed to reach

the activation state, without being changed itself. Proteins that function as catalysts are called enzymes.

Reactant

Product

CatalyzedUncatalyzed

Product

Reactant

Activationenergy

Activationenergy

En

erg

y su

pp

lied

En

erg

y re

leas

ed

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Activation Energy and Catalysis

Peroxidase Enzyme Activity Advanced Inquiry Lab

Peroxidase enzymes are widely distributed in plants and animals, including bacteria, to protect cells against the effects of oxidative stress and cell damage due to hydrogen peroxide.

Certain enzymes within the peroxisome, use O2, and remove hydrogen atoms from specific organic substrates in an oxidative reaction, producing hydrogen peroxide (H2O2)

Peroxidase Enzyme Activity Advanced Inquiry Lab

Peroxidases are easily extracted from turnips and other root vegetables and provide a model enzyme for studying enzyme activity—how the rate of an enzyme-catalyzed reaction depends on biotic and abiotic factors. Enzyme activity studies reflect enzyme structure and function and provide the foundation for understanding the mechanism or theory of enzyme action.

Until next time…