Bioenergetics

Objective:-

To understand the differences between Thermodynamics and Bioenergetics

To know the two Thermodynamics laws (energy exchange)

To understand how the energy of food stuffs are released

 To understand how the energy of food stuffs are converted into the ATP; Substrate level & Oxidative ATP synthesis

To predict and calculate the degree of possibility of a given reaction

To describe Chemiosmotic theory of ATP synthesis

To describe the function of ETC complexes (I, II, III & IV)

To write 4 sentences about the mechanism of  Fo-FI function

To know coupling reaction and the roles of uncouplers

To know and name 4 types of oxidative

 

Biomedical importance of BIOENERGETICS & Oxidation/Reduction:

In human , an amount of ATP approximately equal to the body weight is formed and broken down every 24 hrs.

Brown fat

Thyroid hormones and Uncouplers

Oxygen toxicity and Free radicals

Many drugs, pollutants and chemical carcinogens( Xenobioticts) are metabolized by cytochrome P450 system

Some poisons are inhibitors of oxidative phosphorylation

Phosphagens such as creatine-P

 Extraction and packaging of the energy from food stuffs

 

Why and how we make ATP?

              Glucose +    O₂   ®    CO₂  +  H₂O  + ATP(Energy)

Thermodynamics/ Bioenergetics:

The study of energy transformations that occur in a collection of matter is called Thermodynamics.

The Thermodynamics in living organisms is called Bioenergetics.

 In other words, Bioenergetics is the study of energy in living systems

 Living systems = Environments + Organisms

 

First & second Laws of Thermodynamics:

First Law: Energy cannot be created or destroyed, but only converted to other forms.

This means that the amount of energy in the universe is constant     

Second Law: All energy transformations are inefficient because every reaction results in an increase in entropy and the loss of usable energy (free energy) as heat.

IF:

H = Enthalpy= the total heat of a system

G = Free energy= the amount of usable energy in a system that can be used to perform a work.

S =Entropy = the amount of disorder in a system. In most but not all cases it is heat.

Then somehow:

                            ∆G= G_B-G_A

                            ∆H= H_B-H_A

                            ∆S= S_B-S_A

 

Gibbs equation:

∆G = ∆H - T∆S

Gibbs equation in living organisms

 ∆G = ∆E - T∆S

The relationship between the value of ∆G and the spontaneity of a reaction:

Endergonic Reactions have:         ∆G +

Exergonic Reactions have           :∆G -

At equilibrium state have:             ∆G = 0

 

∆G OR ∆G^o OR ∆G^o’, Which one is more important?

∆G = Free energy difference  of a system in any condition.

∆G^o = Free energy difference of a system in standard condition ( 25C^o and one atmosphere pressure.

∆G^o’ = Free energy difference of a system in standard condition at pH = 7.

NEVER FORGET THAT :

∆G determines the feasibility of a reaction not ∆G^o or ∆G^o’

Cellular Metabolism:

The sum total of the chemical activities of all cells is called Cellular Metabolism.

Anabolic Pathways (Endergonic reactions):

            Those that consume energy to build complicated molecules from simpler compounds such as: Protein, Glycogen & lipid synthesis.

Catabolic Pathways (Exergonic reactions):

     Those that release energy by breaking down complex molecules into simpler compounds such as glycolysis

Most energy from fuel (food) obtained through oxidative  processes

oxidation :

                      * Gain of Oxygen         

                      * Loss of Hydrogen

                      * Loss of electrons

 

Reduction:

                     * Gain of Hydrogen

                     * Gain of electron

                     * Loss of Oxygen

E= Reduction Potential (Redox):

Redox potential measures of the tendency of oxidant to gain electrons, to become reduced, it is a potential energy.

 Electrons move from compounds with lower reduction potential (more negative ) to compounds with higher reduction potential ( more positive).

Reductant     D    oxidant   +   e-

Oxidant  +  e-  D  reductant

Oxidation and reduction must occur simultaneously

DE =Reduction Potential Difference:

DE= E_A - E_D

 

∆E = Redox difference  of a system in any condition.

∆E^o = Redox difference of a system in standard condition ( 25C^o and one atmosphere pressure).

∆E^o’ = Redox difference of a system in standard condition at pH = 7

NEVER FORGET THAT :

∆E determines the feasibility of a reaction not ∆E^o or ∆E^o’.

 and

The more positive the reduction potential difference is, the easier the redox reaction

 

Can we predict the amount of energy that can be released from an oxidation-reduction reaction?

DGº¢ = -nF DEº¢

Where:  n = the number of transferred electron (1,2,3)

F = the Faraday constant that is 96.5 kJ/volt

E = measured in volts

G= measured in KCal or KJ

 In other words energy (work) can be derived from the transfer of electrons and an electron transfer system (ETS) Or :

 Oxidation of foods can be used to synthesize ATP.

Standard Reduction Potential (Eº) of some biologically important compounds

Oxidant                  Reductant         n     Eº, v

NAD⁺                        NADH                 2      -0.32

acetaldehyde          ethanol              2      -0.20

pyruvate                  lactate                2      -0.19

oxaloacetate           malate               2      -0.17

1/2 O₂+2H⁺               H₂O                    2     +0.82

Oxidants can oxidize every  compound with less positive  voltage (above it in Table)

 Reductants can reduce every compound  with a less negative voltage (below it in Table).

 

The enzymes and coenzymes  that are responsible for Oxidation and reduction in living organisms

1- Dehydrogenases (loss of Hydrogen)

2- Oxidases (electron transfer

to molecular oxygen)

3- Oxygenases(gain of Oxygen )

4- Cytochromes (electron transfer )

5- Fe –S centers (electron transfer )

6- CoQ = ubiquinone (Hydrogen transfer )

 

 

Electron Transport Chain (ETC):

Electrons move from a carrier with low redox potential toward carriers with higher redox.

Electrons can move through a chain  of donors and acceptors.

 In the electron transport chain,  electrons flow down a gradient

 

Different ways to make ATP:

Phosphorylation is:

Mechanisms of phosphorylation:

 1- Photophosphorylation (chlorophyll / light-absorbing pigments)

6CO₂+  6H₂O                    C₆H₁₂O₆   +   6O₂ + ATP

2- Substrate-level phosphorylation (in cytosol):

 D~ P + ADP            D + ATP

3-Oxidative phosphorylation (across inner mitochondrial membrane)

Up to now you have combined your physico-chemical knowledge to understand the basis of ATP synthesis

 

 

Continue to part-III………………………………………………………………………