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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.
Principle of Bioenergetics
Chemical energy is used to:
- synthesize complex, highly orderedmacromolecules from _______ precursors.
- concentration/ electrical gradients
- motion
- Heat
- light (______, __________)
Principle of Bioenergetics
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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.
Other Phosphorylated Compounds
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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Other Phosphorylated Compounds
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