Free Energy and ATP

1. Free Energy and ATP But I thought nothing in life is free?!

2. 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

3. 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.

4. 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.

5. Free Energy Equation • Free energy = G • Total energy = H • Entropy = S • Temperature (Kelvin) = T G = H – TS

6. 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.”

7. 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) HOT COLD

8. Is this an endergonic or exergonic reaction?!

9. 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.

10. Endergonic Reaction • Endergonic reactions store energy • ∆G is positive • nonspontaneous • Example: • Cleaning your room!! • Photosynthesis making sugar = + 686 kcal

11. Equilibrium • 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.

12. 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.

13. 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?

14. ATP! • 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.

15. 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

16. 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.

17. 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.

18. 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.