2. CH 13 Bioenergetics

8/8/2019 2. CH 13 Bioenergetics

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Principle of Bioenergetics

Chapter 13

Lehninger

Principles ofBiochemistry

by

Nelson & Cox

Must perform work in order to: ____________

____________ ____________

The ability to_____________and to channel itinto biological work is a fundamental property ofall living organisms

Variety of: energy transductions, conversion of one form to another

takes place in cell.


Chemical energy is used to:

- synthesize complex, highly orderedmacromolecules from _______ precursors.

- concentration/ electrical gradients

- motion

- Heat

- light (______, __________)



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Gibbs free energy, G:

The amount of energy capable of doing work

If the reaction proceeds with release of free (looses) energy(G is Negative)

-______________

If system gains energy (G is positive)

-______________

G=0 (both forward and reverse reactions occur at equal

rates; the reaction is at_____________.

Enthalpy, H(Heat content of the reacting system)

- Number and kinds of __________________ inreactants and products

Exothermic: heat is _________(system looses) in a reaction.

Endothermic- Reacting system ________up heat.

Entropy, S(qualitative expression for the randomness or

disorder in the system)

Gain in Entropy: Products are ____ complex and

______ disordered than reactants.

The order created in a cell (as they grow) iscompensated by the _______ they create in theirsurroundings.


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Relationship : Gibbs free energy, enthalpy &entropy

G &H are in joules/mole or calorie/mole

In biological system

(constant temperature and pressure):

- changes in free energy, enthalpy (H) and entropy (S)are related to each other:

G = H - TS

Tis absolute temperature

Standard free energy is related to theEquilibrium Constant

The composition of reacting system keeps changinguntil _____________ is reached.

At equilibrium:

- the concentration ofreactants and product, and the

- rate offorward and reverse reaction are _____________:

_________change in the system.

Cells Require Sources of Free Energy

Cells use free energy Gwhich also allows topredict the _________ of the reaction.

Heterotrophic Cells get free energy from__________.

Photosynthetic cell get it from_____________.

Both types of cells transform this energy into____

and other energy rich compounds.


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Standard free energy is related to theEquilibrium Constant

Change in the ____________for reaction: G

Standard free energy change : GFor biochemists : GEquilibrium constant : Keq

(For more details and explanation refer to p 491)

Standard free energy is related to the Equilibrium constant

IfG is negative = products have_______free energy

(reaction is spontaneous) all chemical reactions tend to go in adirection of decrease in free energy. Goes _______ direction.

IfG is positive = products have________free energy(reaction will tend to go in _________ direction)

E3

Standard free energy is related to the Equilibrium constant

IfKeq >1: chemical reactions proceed_______.

IfKeq


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Slide 11

E3 alk also about Equilibrium constantETSU, 8/20/2008


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Some thermodynamically favorable(G is large &negative) reactions do not occur atmeasurable rates:

e.g. combustion of firewood to CO2 and H2O

Because activation energy for required for combustion is

__________ than energy available at RT (room temperature).

__________ will provide that activation energy.

Activation energy

In living cells, reaction will be extremely slow ifuncatalyzed, -

- are made to proceed_____by increasing heat

- but by_________the activation energy.

Standard free energy are additive

In case of two sequential reaction theAB and BC with G1 and G2

G values (1 & 2) are ________

For overall reaction AC (B cancels: sequential) Gtotal = G1+ G2

This can explain how a thermodynamically unfavorable(____________) reaction can be driven in forward directionby coupling it to a highly_____________- reaction througha common intermediate.

Consider a example-


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Synthesis ofGlucose 6-phosphate is first step inthe utilization of Glucose

Glucose+ Pi glucose 6-phosphate+ H2O

G= 13.8 kJ/mol

Whi le hydrolysis of ATP is very exorgonic

ATP+ H2O ADP+ Pi G = 30.5 kJ/mol

Both reaction have common intermediate: Pi and H2O

and if sequential will have a:

G=13.8 kJ/mol + (30.5 kJ/mol)=16.7 kJ/molthe overall reaction is __________ (favorable).

Standard free energy are additive

Equilibrium constant K are multiplicative

G is additive but Equilibrium constant (K) are__________________.

By coupling ATP hydrolysis to glucose 6-phosphatesynthesis, the Keq for glucose 6-phosphate formationhas been raised by a factor of about 2x105

Keq1=Glucose+Piglucose 6-phosphate= 3.9x10-3 M-1

Keq2= ATP ADP + Pi = 2.0x105M

For coupled reaction:Keq3=(Keq1)(Keq2)=(3.9x10-3 M-1)(2.0x105 M)

= ________

Phosphoryl Group Transfers and ATP

Heterotrophic cells obtain free energy in chemical formby catabolism of nutrients and use that to make ___from ______ and _____.

ATP then donates this energy to ________ processesas:

__________of metabolic intermediates and macromolecules

from smaller precursors

Transport across membranes against concentration gradients

mechanical motions


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Phosphoryl Group transfers and ATP

Although the hydrolysis of ATP is highly exergonic but ATP is

kinetically_________at pH 7, because-activation energy needed is _______.

- An enzyme is needed to l ower the activation energy.

The concentration of ADP &

Pi in cell are much ______conc. at equilibrium,

favoring hydrolysis

reaction in cell.

Other Phosphorylated Compounds

PEP (Phosphoenolpyruvate) has phosphate ester bond that

hydrolyses to yield enol form of pyruvate which can immediatelytautomerizes to a stable keto form:

Product: more ____ than reactant due to itsexistence in____forms.

Result: ______ standard free energy.


Another 3-C compound, 1,3-bisphosphoglycerateUpon reaction with phosphoric acid:

The product loses a proton to give carboxylateion which has two equal ____________ forms.


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In Phosphocreatine, the P-N bond can behydrolyzed to generate free creatine and Pi.

The release ofPi and________stabilization ofcreatine favors forward reaction.

In all these phosphate releasing reactions :

Several resonance forms available to__ stabilizesthe products relative to reactants therebycontributing to already______standard freeenergy.

Has sulphur atom which replaces oxygen in theester bond has large G.

_______________is oneof the many thioesters

Important in metabolism.

Thioesters


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Hydrolysis reactions with large ve standardfree energy, products are more ________.

ATP provides energy by ______ transfer and notby simple _________.

While some processes do involve ______hydrolysis ofATP

e.g. - Muscle contraction,(Chemical energy is converted into kinetic energy)

- Movement of- enzyme along DNA or of- ribosomes along mRNA.


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Biological Oxidation-Reduction Reactions

1. Phosphoryl groups (_____, ____ etc.)2. Electron transfer in oxidation-reduction:

involves loss/gain of electronsloser = is_________gainer = is_________

It is the direct/indirect result of flow of ________which is responsible for ___________done in livingorganisms.

Source of electron: heterotrophic cells: __________ compounds (food)

Photosynthetic cells: Initial electron donor,

(a chemical species excited by light absorption)

Electrons move from metabolic intermediates tospecialized electron carriers which donate electronsto acceptors with ______________, with release ofenergy.

Biological system has glucose (________) as sourceof electrons.

Biological Oxidation-Reduction Reactions

Biological Oxidations Involve Dehydrogenation:

Carbon in living cell exists in range of oxidation states due to

its ____________ sharing of electrons:

In most of the cases

when Carbon sharesan electron pair, is

_________in favor of

more electronegativeatom (H


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Biological Oxidations involve Dehydrogenation:

In biological system oxidation is synonymous to

___________.

There are also oxidation-reduction reactions which donot involve carbon, e.g. Nitrogen to ammonia:

6H+ + 6e- + N2 2NH3 (N is reduced)

Electrons are transferred from donor toacceptor in one of the following ways :

1. Directly as ___________2. As hydrogens atoms3. As a hydride (:H

), has 2 electrons

4. Through direct combination with_______.

(For More information p 513-514)

All four types occur in cells.

The oxidation ofglucose supplies energy forATP production.

C6H12O6 + 6O2

6CO2 + 6H2O

Energy needed for ATP synthesis (50-60 kJ/mol).

Cellular oxidation of Glucose to CO2

G is -2840 kJ/mol


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Glucose to CO2 conversion is not in ____ high-energyreleasing reaction but ________ tightly controlled

reactions including some oxidation.

Energy released in each step is sufficient for ATPsynthesis from ADP with some extra.

Electrons removed in these oxidation are transferredto specialized carriers:

e.g. NAD+ & FAD

Specialized carriers

Nicotinamide adenine dinucleotide

Flavin adenine dinucleotide

C6H12O6 + 6O2 6CO2 + 6H2O

Universal Electron Carriers

Only ____ types ofuniversal electron carriers- many enzyme catalyzed cellular oxidation.- hundreds of different substrates.

NAD, NADP, FMN and FAD: _____ soluble coenzymes

- NAD, NADP, readily ____ from one enzyme to another

- While FMN, FAD are ___________to enzymes c/a

flavoproteins.

Some ______ soluble quinones:(ubiquinone and Plastoquinone)

Act as electron carriers and proton

donors in__________environment(membranes).

Iron-sulphur proteins andcytochromes:

water soluble orintegral membrane proteins.

Universal Electron Carriers


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NADH and NADPH act with dehydrogenases assoluble Electron Carriers

-NAD and NADP, are composedof two nucleotides joined

together thru their phosphategroup.

Vitamin niacin (B3) is sourceof nicotinamide moiety innicotinamide nucleotides.

Vitamin B3: water soluble.

Adenine

NADH and NADPH act with dehydrogenases assoluble Electron Carriers

- In many cells ratio ofNAD+ to NADH is highwhich favors formation on NADH.

Role in oxidations in__________

- While NADPH is present in greater amountsthan NADP

Role in__________ reactions

Pellagra

Humans do not synthesize sufficient niacin (vitamin B3)(synthesized from ______________).

Maize (corn) is a low

_____________ Diet.

This affects all the NAD(P)dependent dehydrogenases.

Pellagra-Human

Black tongue - dogs(dermititis, diarrhea &

Dimentia---death)

Read (p519)

Role of Alcohol?


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Flavin Nucleotides are tightly bound inFlavoproteins

Flavoproteins catalyzereactions using flavin

mononucleotide (FMN) orflavin adenine dinucletotide(FAD)

- derived from vitaminriboflavin (B2)

Flavoproteins can participateeither in ___- or ___-electrontransfers:

greater diversity

Flavin Nucleotides: tightly bound in Flavoproteins

Certain flavoproteins: act as___________

Cryptochromes:

In plants: mediate effects ofblue lighton plant ________________.

In animals: light on _________________.

Phytolyases (a flavoprotein) use lightenergy for ________chemical defects in ___.

- are activated by _______ absorption.

- Can repair UV-induced DNA-damage.

Flavin Nucleotides: tightly bound inFlavoproteins

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