BIOENERGETIC AND CHEMICAL FOUNDATION

ENERGY FLOW

To perform various task cell require energy to grow, move, synthesis & transportation. In scientific concept energy means capacity to perform work or ability to cause some kind of change to occur.
For cell to form function energy must flow into cell from its surrounding.
Energy occurs in different form, cells obtain energy either in the form of organic molecules that contain chemical energy or energy from photosynthetic organisms as photons of light.
This energy is of two types.
Kinetic energy deals with motion of molecules, thermal radiation etc. Potential energy is the energy stored in bonds connecting atoms.

LAWS OF THERMODYANAMICS

Thermodynamics principle helps us to understand about these energy law & their transformation:

First Law –

Energy can never be created nor be destroyed however it can be transform from one form to another .
Energy of universe is constant, either change occurs in energy form or it’s physical location.
Transformation takes place between various forms of energy such as heat, light, electricity, mechanical energy & chemical energy.
In thermodynamics particular location in which energy changes occurs is reffered as system & rest of the universe is surrounding.
Energy content of an individual system can be changed, but total energy content of system & surrounding remains constant. In cell 1st law is applicable in the sense that energy is transformed from surroundings & is transformed into those forms which is used by cell, for example in autotrophs, light energy is converted into chemical energy which is essentially used by heterotrophs.

Second Law-

1st law does not tells us about the probability that any such process is actually occuring. As a biologist one must like to know the direction of reaction & whether energy is released or absorbed.
This law states that energy event in the universe occurs in the direction that cause the system & surrounding to exhibit a net increase in randomness i.e Entropy.
According to second law the Entropy of system & surrounding always increases but this is not true that entropy of individual system always increase.
It may increase or decrease or remain same .
Free energy or G (Gibbs).
Describes the thermodynamic factors that allow us to apply the second law of thermodynamics to a individual chemical reaction without requiring us to measure the entropy change.
It represents the energy that can be harnessed to do useful work.
For living organisms where pressure and volume remains constant, the change in free energy that accompanies any biological process is determined by two parameters;

Δ E =total internal energy/ enthalpy

S=change in entropy

G= Δ E – TΔS

ΔS; where G = freeen ergy, T=absolute temperature

If Entropy increases then free energy decrease ;

ie, (ΔS= positive) (ΔG=negative)

(ΔE<0; ΔG<0 ; ΔS>0)

& reactions proceeds in the directions that causes decrease in the free energy of the system i.e Exergenic reactions , i.e they realize free energy (products contains less bond energy ) .

It indicate the direction of the reactions i.e breakdown of complex organic molecule into simpler one is exergenic reactions .
If Entropy decreases then free energy increases ;

i.e (ΔS= negative) (ΔG=positive) (ΔE>0);

Such type of chemical reactions are called as Endergenic reactions.
Photosynthetic organism are huge, complex,
Endergenic reactions centers in which ΔG can be made favorable by coupling them to external energy supply i.e light .
ΔG indicate the direction of reactions.
Most biological reaction differ from standard condition, particularly in the concentrations of the reactants.
We can estimate free energy changes for different temperature by using the equation;
ΔG’=ΔG0′ +2.303RT log(product/reactant) where,
R=gas constant,
T= absolute temperature,
ΔG0’=standard free energy,
ΔG’= is measure of actual change in free energy, that occurs with a particular mixture of reactants & products at given concentration, the value of ΔG’ thus varies, depending on the conditions involved.

ΔG0′ is constant under standard conditions.
It can be calculated under conditions of equilibrium.

If 0is substituted in eq (a)for ΔG’

0=ΔG0’+2.303 RT log(product(eq)) ……….. (a)

( reactant(eq))

ΔG0’= -2.303 RT log(product(eq)………. (b)

(reactant(eq)

Equilibrium constant Keq= (product(eq)) ……….. (c)

(reactant(eq))

Keq can be substituted in eq (b)

ΔG0’= -2.303 RT log Keq ………..(d)

(Equilibrium constant at pH=7)

If ΔG0’= positive, direction of reaction , reactant —–> product,

reaction is exergonic i.e Keq>1 & (product)> (reactant);

If ΔG0’= positive, direction of reaction , reactant <—– product,

reaction is endergonic i.e Keq<1 & (product)< (reactant);

ROLE OF ATP IN TRANSFERRING FREE ENERGY

One widely occurring pattern involves the use of high energy phosphorylated compounds that release energy when their phosphate groups are removed.
Such compounds play a key role in transferring energy from thermodynamically favorable to thermodynamically unfavorable processes.
The most common example of such high-energy compound is adenosine triphosphate (ATP) .
The structure of ATP and the reactions involved in the removal of its phosphate groups is hydrolysis reaction i.e exergonic, giving adenosine diphosphate (ADP) & a free phosphate group.
The terminal phosphate of ADP can also be removed in another