The point is to make ATP! Life and Thermodynamics (Ch. 8)

The energy needs of life Organisms are endergonic systems – What do we need energy for? synthesis – building biomolecules reproduction movement active transport temperature regulation

Food = Fuel = Energy

Transformations between kinetic and potential energy More potential energy. Potential energy converted to kinetic energy. Kinetic Energy Converted to Potential Energy Less potential energy

The two laws of thermodynamics (a) First law of thermodynamics: Energy can be transferred or transformed but neither created nor destroyed. Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. (b) Chemical energy Heat co 2 H2OH2O +

H / 2 O 2 2 H 1 / 2 O 2 (from food via NADH) 2 H e – 2 H + 2 e – H2OH2O 1 / 2 O 2 Controlled release of energy for synthesis of ATP ATP Electron transport chain Free energy, G (b) Cellular respiration (a) Uncontrolled reaction Free energy, G H2OH2O Explosive release of heat and light energy + How Food Becomes Energy

(a) A closed hydroelectric system ∆G < 0∆G = 0 (b) An open hydroelectric system ∆G < 0 A multistep open hydroelectric system (c) ∆G < 0 Open Systems and Equilibrium

Where do we get the energy from? Work of life is done by energy coupling – use exergonic (catabolic) reactions to fuel endergonic (anabolic) reactions ++ energy + + digestion synthesis

ATP Living economy Fueling the body’s economy – eat high energy organic molecules – break them down – capture released energy in a form the cell can use Need an energy currency – a way to pass energy around – need a short term energy storage molecule Whoa! Hot stuff!

ATP high energy bonds How efficient! Build once, use many ways Adenosine TriPhosphate – modified nucleotide nucleotide = adenine + ribose + P i  AMP AMP + P i  ADP ADP + P i  ATP – adding phosphates is endergonic

How does ATP store energy? P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O Each negative PO 4 more difficult to add – a lot of stored energy in each bond most energy stored in 3rd P i 3rd P i is hardest group to keep bonded to molecule Bonding of negative P i groups is unstable – spring-loaded – P i groups “pop” off easily & release energy Instability of its P bonds makes ATP an excellent energy donor I think it’s a bit unstable… don’t you? AMP ADPATP

How does ATP transfer energy? P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O 7.3 energy + P O–O– O–O– O –O–O ATP  ADP – releases energy ∆G = -7.3 kcal/mole Fuel other reactions Phosphorylation – released P i can transfer to other molecules destabilizing the other molecules – enzyme that phosphorylates = “kinase” ADPATP

Can’t store ATP  good energy donor, not good energy storage too reactive transfers P i too easily only short term energy storage  carbohydrates & fats are long term energy storage ATP / ADP cycle A working muscle recycles over 10 million ATPs per second Whoa! Pass me the glucose (and O 2 )! ATP ADP PiPi kcal/mole cellular respiration

Cells spend a lot of time making ATP! What’s the point? The point is to make ATP!

H+H+ catalytic head rod rotor H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP synthase ATP But… How is the proton (H + ) gradient formed? ADP P + Enzyme channel in mitochondrial membrane – permeable to H + – H + flow down concentration gradient flow like water over water wheel flowing H+ cause change in shape of ATP synthase enzyme powers bonding of P i to ADP: ADP + P i  ATP

That’s the rest of my story! Any Questions?

Review Questions

1. Which of the following reactions could be coupled to the reaction ATP + H2O → ADP + Pi (-7.3 kcal/mol)? A.A + Pi → AP (+10 kcal/mol) B.B + Pi → BP (+8 kcal/mol) C.CP → C + Pi (-4 kcal/mol) D.DP → D + Pi (-10 kcal/mol) E.E + Pi → EP (+5 kcal/mol)

2. Assume that the reaction has a ∆G of -5.6 kcal/mol. Which of the following would most likely be true? * A.The reaction could be coupled to power an endergonic reaction with a ∆G of +6.2 kcal/mol. B.The reaction could be coupled to power an exergonic reaction with a ∆G of +8.8 kcal/mol. C.The reaction would result in a decrease in entropy (S) and an increase in the total energy content (H) of the system. D.The reaction would result in an increase in entropy (S) and a decrease in the total energy content (H) of the system. E.The reaction would result in products (C + D) with a greater free-energy content than in the initial reactants (A + B).

3.A particularly obnoxious acquaintance claims that since life is able to spontaneously create more ordered structures and systems from less ordered structures and systems, that the laws of thermodynamics are wrong, or at the very least do not apply to living systems, and implies that this observation means that a higher power has created life. Briefly explain why this person is an idiot, and where the flaw(s) in his logic lie.