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Free Energy and ATP. But I thought nothing in life is free?!. Spontaneous vs. Nonspontaneous. Spontaneous processes : those that can occur without outside help example: your room getting messy! increases stability of a system

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free energy and atp

Free Energy and ATP

But I thought nothing in life is free?!

spontaneous vs nonspontaneous
Spontaneous vs. Nonspontaneous
  • Spontaneous processes: those that can occur without outside help
    • example: your room getting messy!
    • increases stability of a system
  • Nonspontaneous processes: those that can only occur if energy is added to a system
    • example: cleaning up your room!
    • decreases stability of a system
free energy
Free Energy
  • Free energy provides a criterion for measuring spontaneity of a system.
  • Free energy is the portions of a system’s energy that is able to perform work when temperature is uniform throughout the system.
free energy examples
Free Energy Examples
  • High Free Energy:
    • compressed springs
    • separated charges
  • These are unstable and tend to move toward a more stable state, one with less free energy.
free energy equation
Free Energy Equation
  • Free energy = G
  • Total energy = H
  • Entropy = S
  • Temperature (Kelvin) = T

G = H – TS

change in free energy
Change(∆) in Free Energy

∆G = Gfinal state - Gstarting state

Or… ∆ G = ∆ H - T ∆ S

  • For a system to be spontaneous, the system must either give up energy (decrease in H), give up order (decrease in S), or both.
    • ∆ G must be negative.
    • The more negative, means the more work can be done.
    • Nature runs “downhill.”
chemical reactions
Chemical Reactions
  • Chemical reactions can be classified based on free energy:
    • exergonic reaction: proceeds with a net release of free energy (∆G is negative)
    • endergonic reaction: absorbs free energy from its surroundings (∆G is positive)



exergonic reaction
Exergonic Reaction
  • ∆Gis negative
  • Example: breakdown of sugar
    • ∆G = -686 kcal/mol
    • Through this reaction 686 kcal have been made available to do work in the cell.
endergonic reaction
Endergonic Reaction
  • Endergonic reactions store energy
  • ∆G is positive
  • nonspontaneous
  • Example:
    • Cleaning your room!!
    • Photosynthesis making sugar =

+ 686 kcal

  • A system at equilibrium is at maximum stability.
      • forward and backward reactions are equal
      • no change in the concentration of products or reactants
  • At equilibrium ∆G = 0 and the system can do no work.
    • Movements away from equilibrium are nonspontaneous and require the addition of energy from an outside energy source (the surroundings).
    • Reactions in closed systems eventually reach equilibrium and can do no work.
equilibrium in cells
Equilibrium in Cells
  • A cell that has reached metabolic equilibrium has a ∆G = 0 and is dead!
    • Metabolic disequilibrium is one of the defining features of life.
  • Cells maintain disequilibrium because they are open with a constant flow of material in and out of the cell.
  • A cell continues to do work throughout its life.
cells have to work
Cells have to work?!
  • A cell does three main kinds of work:

1. Mechanical work: beating of cilia, contraction of muscle cells, and movement of chromosomes.

2. Transport work: pumping substances across membranes against the direction of spontaneous movement.

    • Chemical work:driving endergonic reactions such as the synthesis of polymers from monomers.
  • What powers all this work?
  • The energy that powers cellular work is ATP!
  • ATP (adenosine triphosphate) is a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups.
how does atp release energy
How does ATP release energy?
  • The bonds between phosphate groups can be broken by hydrolysis.
    • Hydrolysis of the end phosphate group forms adenosine diphosphate [ATP -> ADP + Pi] and releases 7.3 kcal of energy per mole of ATP under standard conditions.
    • ∆Gis about -13 kcal/mol
why does this release energy
Why does this release energy?
  • Bonds are unstable… their hydrolysis yields energy because the products are more stable.
  • The phosphate bonds are weak because each of the three phosphate groups has a negative charge.
  • Their repulsion contributes to the instability of this region of the ATP molecule.
how is the energy harnessed
How is the energy harnessed?
  • the energy from the hydrolysis of ATP is coupled directly to endergonic processes by transferring the phosphate group to another molecule.
  • This molecule is phosphorylated.
    • now more reactive.
where does the atp come from
Where does the ATP come from?
  • ATP is continually regenerated by adding a phosphate group to ADP.
  • Energy for renewal comes from catabolic reactions in the cell (breakdown of sugar!).
    • In a working muscle cell the entire pool of ATP is recycled once each minute, over 10 million ATP consumed and regenerated per second per cell.