Free Energy and ATP

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# Free Energy and ATP - PowerPoint PPT Presentation

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

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
• 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 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
• 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 = G
• Total energy = H
• Entropy = S
• Temperature (Kelvin) = T

G = H – TS

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 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

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 reactions store energy
• ∆G is positive
• nonspontaneous
• Example:
• Cleaning your room!!
• Photosynthesis making sugar =

+ 686 kcal

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.
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?!
• 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?
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.
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?
• 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?
• 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?
• 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.