8.2 and 8.3- Free energy and ATP

Energy Change (Δ)

what is needed to determine spontaneous and non spontaneous reactions

J Willard Gibbs

defined a function called the free energy of a system (without considering the surroundings)

A living systems free energy (G)

a portion of energy in the cell that can do work when temp and pressure is uniform

∆G

The change in free energy

∆H

change in enthalpy (in biological systems this is equivalent to total energy)

∆S

change in entropy

T

temperature in Kelvin

∆G = ∆H – T∆S

Formula

When ∆G is negative

(negative change in free energy) the process is spontaneous

For there to be a negative ∆G

the system either gave up some total energy (H decrease) or it gave up order and S (+T∆S) increases. Both can happen

Because of their negative ∆G

these spontaneous reactions can be harnessed to preform work

another way to think of ∆G

it is the difference between the free energy of the final products and the energy of the initial (reactants) ∆G = G products – G reactants

-∆G only occurs

when the process involves a loss of free energy during the change from reactants to products

every spontaneous process

decreases the systems free energy

Free energy is a measure

of a systems instability, its tendency to change into a more stable state

unstable systems

Higher G

More stable systems

lower G

As the free energy decreases (-∆G)

the stability of a system increases

Equilibrium

in the state of maximum stability

A process is spontaneous and can preform work only when

it is moving towards equilibrium ( G is decreasing )

What is this image showing

More free energy, less stable, and greater work capacity. Energy is released in this process.

What is this image showing

Less free energy, more stable, less work capacity. falling does not need any energy, neither does diffusion

Exergonic Reaction

(energy outward) proceeds with a net release of free energy to its surroundings and is spontaneous

Endergonic reaction

(energy inward) proceeds with net absorption of free energy form its surroundings and is nonspontaneous

What type of reaction is this

Exergonic Reaction (energy is released and spontaneous)

What type of reaction is this

Endergonic Reaction (energy required, nonspontaneous)

reactions in an isolated (closed) system eventually

reach equilibrium and then do not work

Living cells are not in equilibrium

because they are open systems and are in a constant flow of materials in and out

metabolism is

never at equilibrium (it is death)

catabolic pathway in a cell

releases free energy in a series of reactions

what type of system is this

closed hydroelectric system

what type of system is this

an open hydro electric system

what type of system is this

multistep open hydroelectric system

the cell does three kinds of work

• chemical

• transport

• mechanical

Chemical work

pushing endergonic reactions

transport work

such as pumping substances across membranes against gradients

mechanical

such as contraction of muscle cells

Energy coupling

the use of exergonic process to drive an endergonic process

what mediates most energy coupling

ATP

ATP is composed of

one ribose (sugar), one adenine (nitrogen base), and three phosphate groups

The bonds of the phosphates on ATP

can be broken by hydrolysis

free energy is released when

ATP is hydrolyzed to from ADP and inorganic phosphate

the release of energy comes from

the change to a state of lower free energy not from the phosphate bonds themselves

what is this

the structure of ATP

what is this

they hydrolysis of ATP

the energy from the exergonic chemical reaction and ATP hydrolysis

can be coupled with and used to drive an endergonic chemical reaction

Overall the coupled chemical reactions

are exergonic

ATP drives endergonic reactions

by phosphorylation

phosphorylation

the transferring of a phosphate group to some other molecule such as reactant in a chemical reaction

the recipient molecule with the phosphate group attached to it

is less stable with more free energy and is now called phosphorylated intermediate

ATP is renewable and is regenerated by

the addition of a phosphate group to ADP

the energy to phosphorylate ADP to make ATP comes from

catabolic reactions in the cell