bioenergetics_10_2

8/7/2019 bioenergetics_10_2

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Energetics of Living System



Energy Coupling:



ATP + H2O ↔↔↔↔ ADP + Pi ∆G0 = -30.5 kJ/mol

Pi + glucose ↔↔↔↔ glucose-6-P + H2O ∆G0 = +14 kJ/mol

Coupled reaction:

ATP + glucose ↔↔↔↔ ADP + glucose-6-P ∆G0 = -16.5 kJ/mol

Energy Coupling:

Half-reactions



Reaction 1: ATP + H2O ↔↔↔↔ ADP + Pi

K’eq1 = [ADP][Pi]/[ATP] (note water not considered)= 2 x 105 M

Reaction 2: Pi + glucose ↔↔↔↔ glucose-6-P + H2O

K’eq2 = [glucose-6-phosphate]/[glucose][Pi]

= 3.9 x 10-3 M-1

So for the coupled reaction,K’eq = K’eq1 x K’eq2 = 7.8 x 102





Transport of an ion S across a membrane from side 1 to side 2,

The free energy change is:

R = gas constant, T = temperature, Z = charge on the ion,

F = Faraday constant, ∆Ψ∆Ψ∆Ψ∆Ψ = voltage.

∆∆∆∆G = R T ln + Z F ∆Ψ∆Ψ∆Ψ∆Ψ[S]1

[S]2

S1 S2

Side 1 Side 2

Energy Coupling:

Many a time ∆G is positive as [S]2

>> [S]1



Active Transport through ion pumps: Spontaneous ATP hydrolysis (negative∆G) is coupled to (drives) ion flux against a gradient (positive ∆G).

S1 S2

ATP

ADP + Pi

active

transport

Energy Coupling:



H+1 H+

2

ATP

ADP + Pi

ATP

synthesis

Pump working in opposite direction Engine:

ATP synthesis: Spontaneous H+ flux (negative ∆G) is coupled to

(drives) ATP synthesis (positive ∆G).

Energy Coupling:





Phosphoanhydride bonds have a large negative ∆∆∆∆G’0 of hydrolysis.Phosphoanhydride linkages are said to be "high energy" bonds”.

"High energy" bonds are represented by the "~" symbol.

~P represents a phosphate group with a large negative ∆G of hydrolysis.

N

NN

N

NH2

O

OHOH

HHH

CH2

H

OPOPOP-O

O

O- O-

O O

O-

adenine

ribose

ATPadenosine triphosphate

phosphoanhydride

bonds (~

Energetics of High Energy Molecules



ATP ADP + Pi ∆G0 = -30.5 kJ/mol

ATP AMP + PPi ∆G0 = -32.3 kJ/molPPi 2 Pi ∆G0 = -33.6 kJ/molAMP Adenosine + Pi

∆G0 -9.2 kJ/mol

Energetics of ATP

Factors in the large negative ∆G0 :

• electrostatic repulsion.

• stabilization of products by

resonance.



ATP ADP + Pi ∆G0 = -30.5 kJ/mol

Concentration of cellular Pi (remains almost constant), [Pi] = 10-2 M

Concentration of ATP, [ATP] = 10-2 MConcentration of ADP, [ADP] = 10-5 M

R = 8.3 J.mol-1

.K-1

; T = 310 K

∆G = ∆G0 + RT ln ([ADP][Pi]/[ATP])= -30.5 + 8.3*3108ln(10-5) = - 60 kJ/mol

Energetics of ATP



Displacement from equilibrium gives the cell its ability to do work!

System Away from Equilibrium

For ATP hydrolysis to ADP

K’eq = 2x105 M,For constant [Pi] = 0.01 M[ADP]eq /[ATP]eq= 2x105 /0.01

= 2x107

M

In the example in last slide:

[ADP]/[ATP] = 10-3

G

Excess ATP Excess ADP

[ADP]/[ATP]

Equilibrium





Other High Energy Molecules

ATP is intermediate among examples.

ATP can thus act as a Pi donor, & ATP can be synthesized by Pi

transfer, e.g., from PEP.

Compound∆∆∆∆G

o' of phosphate

hydrolysis, kJ/mol

Phosphoenolpyruvate (PEP) −−−− 61.961.961.961.9

Phosphocreatine −−−− 43.143.143.143.1

Pyrophosphate −−−− 33.533.533.533.5

ATP (to ADP) −−−− 30.530.530.530.5

Glucose-6-phosphate −−−− 13.813.813.813.8

Glycerol-3-phosphate −−−− 9.29.29.29.2



PEP

Pyruvate

ADP

ATP

Glu-6-phos

Glucose

C

C

O O−

OPO32−

CH2

C

C

O O−

O

CH3

C

C

O O−

OH

CH2

ADP ATP

H+

PEP enolpyruvate pyruvate

Coupling in series

Many of this type of coupled reactions involve multi-enzyme complex



Making of a nano-motor

ATP Synthase:

Membrane spanning multi-protein complex.Synthesize ATP from ADP, using H+ gradient.

The synthesis is reversible.

The complex rotates during reaction.

ATP synthase based nano-motor:

Fixed the multi-protein complex on glass

slide.

Added a long fluorescence labeled Actinfilament as propeller.

In presence of excess ATP, ATP get

hydrolyzed with rotational motion of the

protein complex.

bioenergetics_10_2

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