The Energetics of Life Part One: Theory

Big Questions What do living systems require to remain functional (aka “living”)? Why are these things needed?

Matter and Energy Are Required energy

Life is a highly ordered system.

How is order maintained? Life is built on chemical reactions that transform energy from one form to another Constant energy input is required organic molecules  ATP & organic molecules sun solar energy  ATP & organic molecules

The inevitable result of loss of order….

Metabolism Chemical reactions of life – forming bonds between molecules anabolic reactions Ex: Dehydration synthesis – breaking bonds between molecules catabolic reactions Ex: Hydrolysis That’s why they’re called anabolic steroids!

Examples  dehydration synthesis (synthesis)  hydrolysis (digestion) + H2OH2O + H2OH2O enzyme

Chemical reactions & energy Some chemical reactions release energy – exergonic – digesting polymers – hydrolysis = catabolism Some chemical reactions require input of energy – endergonic – building polymers – dehydration synthesis = anabolism digesting molecules= LESS organization= lower energy state building molecules= MORE organization= higher energy state

Life Obeys 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 +

How is this avoided?

(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

Food = Matter AND Energy Together

Which must be greater in a living system? This? Or This?

The Calculus of Life If: More food than energy expenditure. Then: Order maintaned  Growth  (Reproduction) If: More energy expenditure than food. Then: Order lost  Disease  Death

Energy & life Organisms require energy to live – where does that energy come from? coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy) ++ energy + + digestion synthesis

It’s all about FREE Energy Free Energy (G) is the energy that can be used to do things in a living system. Exergonic: Reactions that release G (where ΔG is -) Endergonic: Reactions that absorb G (where ΔG is +) ATP  ADP + P i ΔG = -7.3 kcal/mol* *in laboratory conditions

Endergonic vs. exergonic reactions exergonic endergonic - energy released - digestion - energy invested - synthesis -G-G  G = change in free energy = ability to do work +G+G

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

Multiple Steps Lead to More Control

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

Coupling in living systems (HIGHLY SCIENTIFIC):

RAWR! I Am Ferocious! Ferociously Questing For Answers, that is!

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.

4.Proposed: All organisms require a constant supply of free energy to maintain organization, grow and reproduce. a. Compare how free energy is used in each of these contexts. b. Provide an example of each.