ENERGETICSENERGETICS

Laws of ThermodynamicsLaws of Thermodynamics #1 – Energy can be transferred #1 – Energy can be transferred

and transformed, but not created and transformed, but not created or destroyed. (Conservation of or destroyed. (Conservation of energy)energy)

#2 – Every energy transfer #2 – Every energy transfer /transformation increases the /transformation increases the entropy (disorder) of the entropy (disorder) of the universe.universe.

Coupled ReactionsCoupled ReactionsLiving organisms appear to “cheat” the thermodynamic laws because they develop “order”, however, they are essentially “open systems” and receive and release energy by coupling reactions of metabolism.

MetabolismMetabolism All the chemical processes in the All the chemical processes in the

body can be categorized as body can be categorized as either either anabolicanabolic (energy-requiring (energy-requiring in order to build up) or in order to build up) or cataboliccatabolic (energy-releasing for (energy-releasing for breakdown).breakdown).

They work in concert with each They work in concert with each other to meet the needs of the other to meet the needs of the organism.organism.

RespirationRespiration

The process of extracting stored The process of extracting stored energy from glucose to form ATPenergy from glucose to form ATP

CC66HH1212OO66 + 6O + 6O22 6CO6CO22 + 6H + 6H220 0

+ ATP(energy)+ ATP(energy)

Aerobic RespirationAerobic Respiration

Consists of 3 phases Consists of 3 phases GlycolysisGlycolysisKrebs CycleKrebs CycleOxidative Phosphorylation aka Oxidative Phosphorylation aka

Electron Transport ChainElectron Transport Chain

GlycolysisGlycolysis

Literally means “sugar-breaking”Literally means “sugar-breaking” Glucose is broken down in a Glucose is broken down in a

series of reactions, each by an series of reactions, each by an enzyme. Magnesium ions (Mgenzyme. Magnesium ions (Mg2+2+) ) are cofactors that aid enzyme are cofactors that aid enzyme action.action.

Takes place in the cytoplasm.Takes place in the cytoplasm.

The final product from the breakdown of glucose is pyruvic acid.

In order to start the reactions some activation energy is supplied in the form of 2 ATP molecules.

Glycolysis SummaryGlycolysis Summary 2 ATP supply energy.2 ATP supply energy. 2 NADH (coenzyme) are 2 NADH (coenzyme) are

produced as electrons are produced as electrons are released during the breakdown.released during the breakdown.

4 ATP are produced.4 ATP are produced. 2 pyruvic acid molecules (3 C) 2 pyruvic acid molecules (3 C)

result.result. Net gain of 2 ATP.Net gain of 2 ATP.

CrossroadsCrossroads Depending on the presence of Depending on the presence of

oxygen, determines what oxygen, determines what happens to the pyruvic acid next.happens to the pyruvic acid next.

Without oxygen, the process of Without oxygen, the process of fermentation will occur. We will fermentation will occur. We will explore that process later.explore that process later.

But we can extract more energy, But we can extract more energy, if Oif O22 is present, let’s take a look! is present, let’s take a look!

Pyruvic acid (pyruvate) binds to Pyruvic acid (pyruvate) binds to coenzyme A to form acetyl CoA, coenzyme A to form acetyl CoA, releasing COreleasing CO22 and electrons and electrons (picked up by NADH) just prior to (picked up by NADH) just prior to entering the cycle. (2 C)entering the cycle. (2 C)

Kreb’s CycleKreb’s Cycle This cycle of reaction occurs in This cycle of reaction occurs in

the matrix of the mitochondrion.the matrix of the mitochondrion. Although the Kreb’s cycle does Although the Kreb’s cycle does

not use oxygen directly, the not use oxygen directly, the molecules required to keep it molecules required to keep it running, do require it in order to running, do require it in order to be recycled.be recycled.

Kreb’s Cycle Kreb’s Cycle In the course of the cycle, the In the course of the cycle, the

initial molecule (Acetyl CoA) is, initial molecule (Acetyl CoA) is, first combined with a 4C first combined with a 4C compound (Oxaloacetate) to compound (Oxaloacetate) to form a 6C compound (Citric form a 6C compound (Citric Acid*) and then subsequently Acid*) and then subsequently broken apart, piece by piece w/ broken apart, piece by piece w/ more energy and COmore energy and CO2 2 released.released.

*Kreb’s cycle aka Citric Acid Cycle.

Watch the cycle in motion.Watch the cycle in motion.

Please note that this animation is oversimplified, but you should see the basic breakdown of the molecule and the subsequent results.

Kreb’s Cycle* - Kreb’s Cycle* - Intermediate ReactionsIntermediate Reactions

The breakdown reactions can generally be The breakdown reactions can generally be categorized as one of the three:categorized as one of the three:

PhosphorylationPhosphorylation RedoxRedox IsomerizationIsomerization*also Glycolysis intermediate *also Glycolysis intermediate

reactionsreactions

A Closer LookA Closer Look Phosphorylation – Phosphorylation –

changes the shape of changes the shape of the molecule, thus the molecule, thus allowing work to be allowing work to be performed.performed.

A Closer LookA Closer Look Redox reactions release energy when Redox reactions release energy when

electrons move closer to electronegativeelectrons move closer to electronegativeatoms.atoms. The loss of electrons is called The loss of electrons is called oxidation.oxidation. The addition of electrons is called The addition of electrons is called reductionreduction.. More generally: Xe- + Y -> X + Ye-More generally: Xe- + Y -> X + Ye- X, the X, the electron donorelectron donor, is the , is the reducing agentreducing agent and and

reduces Y.reduces Y. Y, the Y, the electron recipientelectron recipient, is the , is the oxidizing agentoxidizing agent and and

oxidizes X.oxidizes X. If the degree of electron sharing changes it is If the degree of electron sharing changes it is

also considered a redox reaction.also considered a redox reaction.

A Closer LookA Closer Look An example of redox is when hydrogen An example of redox is when hydrogen

atoms are stripped from glucose and atoms are stripped from glucose and passed to a coenzyme, like NAD+ passed to a coenzyme, like NAD+ (nicotinamide adenine dinucleotide).(nicotinamide adenine dinucleotide).

Enzymes strip two hydrogen atoms from Enzymes strip two hydrogen atoms from glucose, pass two electrons and one glucose, pass two electrons and one proton to NAD+ and release H+.proton to NAD+ and release H+.

This changes the oxidized form, NAD+, This changes the oxidized form, NAD+, to the reduced form NADH.to the reduced form NADH.

A Closer LookA Closer Look Isomerization – molecule changes shape but Isomerization – molecule changes shape but

retains the same molecular formula.retains the same molecular formula.

Kreb’s Cycle SummaryKreb’s Cycle Summary The released energy is picked up by The released energy is picked up by

1 ATP, 3 NADH and 1 FADH1 ATP, 3 NADH and 1 FADH22.. 1 molecule of CO1 molecule of CO22 is released. The is released. The

COCO22 is considered waste and we is considered waste and we exhale it.exhale it.

Since two molecules of pyruvate, Since two molecules of pyruvate, from the 1 glucose molecule, go from the 1 glucose molecule, go through this cycle, the amounts through this cycle, the amounts above are actually doubled.above are actually doubled.

A Closer A Closer LookLook

Summary so far…Summary so far…

GlucoseGlucoseMoleculeMolecule

ATPATP NADHNADH FADHFADH22

2 pyruvate

6 Carbondioxide

Net gain of 4:

4-2=2

glycolysis

2 Kreb’s

10 total:

2 glycolysis

8 Kreb’s

2 Kreb’s

Electron Transport ChainElectron Transport Chainaka Electron Transport Systemaka Electron Transport System

Occurs in the cristae of Occurs in the cristae of mitochondrion.mitochondrion.

Electrons from NADH & FADHElectrons from NADH & FADH22 are passed (like a hot potato) are passed (like a hot potato) through a chain of cytochrome through a chain of cytochrome molecules.molecules.

This regenerates NAD+ and FAD This regenerates NAD+ and FAD so that they can be reused in so that they can be reused in glycolysis and Kreb’s cycle.glycolysis and Kreb’s cycle.

ETC or ETSETC or ETS

Oxygen is needed to accept the Oxygen is needed to accept the electrons, together with H+ ions, electrons, together with H+ ions, at the end of the chain, forming at the end of the chain, forming waterwater. .

More importantly, a lot of ATP is More importantly, a lot of ATP is generated through this process generated through this process called called oxidative phosphorylationoxidative phosphorylation..

A Closer LookA Closer Look

•Electrons carried by NADH are transferred to the first molecule in the electron transport chain, flavoprotein.

•The electrons carried by FADH2 have lower free energy and are added to a later point in the chain.

Oxidative Oxidative PhosphorylationPhosphorylation

The maximum output from The maximum output from ox-phos is 3 ATP/NADH and 2 ox-phos is 3 ATP/NADH and 2

ATP/FADHATP/FADH22

Calculate how many ATP can be Calculate how many ATP can be produced during this process produced during this process from the 1 molecule of glucosefrom the 1 molecule of glucose..

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ChemiosmosisChemiosmosis A major part of oxidative A major part of oxidative

phosphorylation, this basic phosphorylation, this basic process also occurs in process also occurs in chloroplasts.chloroplasts.

The energy lost from electrons The energy lost from electrons passing through the ETS, is used passing through the ETS, is used to phosphorylate to phosphorylate

ADP to ATP. (coupling reactions)ADP to ATP. (coupling reactions)

Chemiosmosis involves coupled Chemiosmosis involves coupled reactions, where the products of reactions, where the products of one reaction are used in another one reaction are used in another reaction.reaction.

In this case, the initial products In this case, the initial products are Hare H++ ions, which are released ions, which are released from NADH and FADHfrom NADH and FADH22..

These protons are pumped out of These protons are pumped out of the fluid matrix, across the the fluid matrix, across the cristae, to the intermembrane cristae, to the intermembrane space of the mitochondrion.space of the mitochondrion.

A pH and electrical gradient is A pH and electrical gradient is formed as the protons formed as the protons accumulate, forming a reservoir accumulate, forming a reservoir of potential energy.of potential energy.

The protons flow back into the The protons flow back into the matrix through channel proteins matrix through channel proteins called called ATP synthases.ATP synthases.

This flow generates the energy This flow generates the energy to produce ATP.to produce ATP.

At the end of the ETS, the At the end of the ETS, the moving electrons, which first moving electrons, which first served to provide the Hserved to provide the H++ ions ions (protons) when the bonds of (protons) when the bonds of NADH and FADHNADH and FADH22 were broken, were broken, are transferred to oxygen and are transferred to oxygen and coupled with the pumped Hcoupled with the pumped H++ ions ions (back in the matrix), form water.(back in the matrix), form water.

A Closer A Closer LookLook

http://www.youtube.com/watch?v=3y1dO4nNaKY

Complete oxidation of glucose releases 686 kcal per mole.

Formation of each ATP requires at least 7.3 kcal/mole.

Efficiency of respiration is 7.3 kcal/mole x 38 ATP/glucose/686 kcal/mole glucose = 40%.

The other approximately 60% is lost as heat.

Cellular respiration is remarkably efficient in energy conversion.

How efficient is respiration in How efficient is respiration in generating ATP?generating ATP?

Whew!Whew! Now you can see why cell Now you can see why cell

respiration leads to some of the respiration leads to some of the top 40 ways you know you’ve top 40 ways you know you’ve been traumatized by AP Biology.been traumatized by AP Biology.

In the end, if you remember In the end, if you remember nothing else, remember what nothing else, remember what results after each phase or cycle.results after each phase or cycle.

It’s not quite over yet, remember we said that there is an alternative path if no oxygen was present? Well…….

FERMENTATIONFERMENTATION

How Glycolysis keeps going if there How Glycolysis keeps going if there is no oxygen.is no oxygen.

When there is no Oxygen When there is no Oxygen why is Fermentation why is Fermentation

necessary?necessary?W/O OW/O O22, glycolysis is the ONLY chemical reaction to release energy from , glycolysis is the ONLY chemical reaction to release energy from

glucose.glucose.

Cells need to continuously carry out glycolysis, but eventually the NAD can

be used up.If all the NAD is used up, then glycolysis

jams or stops.

Why would it be disastrous for the Why would it be disastrous for the cell if glycolysis stops?cell if glycolysis stops?

It would run out of energy.

What does Fermentation do in What does Fermentation do in order to help glycolysis order to help glycolysis

continue?continue? In Fermentation, chemical reactions occur In Fermentation, chemical reactions occur

that free up the NAD, thus regenerating it for that free up the NAD, thus regenerating it for use in glycolysis.use in glycolysis.

The electron energy released from NADH+ The electron energy released from NADH+ (What NAD is called when it carries the high (What NAD is called when it carries the high energy electrons)energy electrons)

is put back into pyruvic acid. This chemical is put back into pyruvic acid. This chemical reaction results in a new product.reaction results in a new product.

Fermentation ONLY occurs if there is no Fermentation ONLY occurs if there is no oxygen.oxygen.

Products of FermentationProducts of Fermentation In animals, the new product formed is In animals, the new product formed is

lactic acid.lactic acid. This often forms in muscles when they can’t This often forms in muscles when they can’t

get the oxygen they need fast enough.get the oxygen they need fast enough. Lactic acid accumulating in muscles is Lactic acid accumulating in muscles is

painful, but this chemical can later be painful, but this chemical can later be broken down to extract energy when broken down to extract energy when enough oxygen is present.enough oxygen is present.

Products of FermentationProducts of Fermentation In yeast, the new products formed are In yeast, the new products formed are

alcohol and carbon dioxide.alcohol and carbon dioxide. People put both these products to use People put both these products to use

to make wines and cause bread dough to make wines and cause bread dough to rise.to rise.

Fermentation ReviewFermentation Review In your notes write your answers in your own words.In your notes write your answers in your own words.

How does fermentation help a cell release energy from glucose?

Compare and contrast lactic acid fermentation

and alcoholic fermentation.What would happen to fermenting wine

if there was an air leak in the fermentation tank?