Work ≠ Free

Gibbs Free Energy (ΔG) Otherwise known as the “available energy” If ΔG is negative, the products of the reaction are less complex (have less potential energy) and energy is available for cellular work If ΔG is positive, products have more potential energy than reactants and energy must be paid in Example: The “cost” of making glucose via photosynthesis is +686 kcal/mol

How do cells “pay” for cellular work?

The Rai of Yap

How is glucose analogous to the Rai or the $100,000 Bill?

Overpaying Cellular Currency Average Activation Energy required by cellular reactions 1.6 kcal/mol Average Potential Energy of Glucose 686 kcal/mol Using glucose to meet the activation energy needs of cells is wasteful and inherently unstable

The solution: Make “change” by transferring the energy of glucose to molecules of Adenosine Triphosphate (ATP)

ATP Form & Function Form: ATP is a polymer Function: transfer a more appropriate amount of energy to power cellular reactions ΔG = -7.3 kcal/mol (vs kcal/mol from glucose) Like enzymes, ATP may be re- used

Polymer Structure of ATP Ribose (5 pentose sugar) Adenine (nitrogenous base) 3 Phosphate (PO 4 ) groups Since all three phosphate groups are negatively charged, high potential energy bonds are required to keep them attached to the molecule

Transfer of Energy: Phosphorylation The energy stored in ATP is “used” by breaking off one of the phosphate groups ATP  ADP + P i kcal/mol (ΔG) The high kinetic energy of the phosphate group is transferred to the substrate, allowing it to exceed E A

How can ATP be “recharged”?

ATP-ADP Cycle

Recycling of ATP While only around 50 grams of ATP are in the body at any given time, 2 x molecules or >160kg of ATP is formed in the human body daily A cell recycles around 10 million ATP/sec/cell

ADP The “leftover” molecule is Adenosine Diphosphate (ADP) and has less energy than ATP Like a mousetrap that has been “sprung”, it may be reset by increasing its potential energy

Catabolism: Recharging ATP Energy is liberated from the bonds of glucose during cellular respiration in the mitochondria The enzyme ATP SYNTHETASE reduces the E A required to put a phosphate group back onto ADP

In Summary… Chemical reactions need to be “paid for”, even if it is just the activation energy Paying for chemical reactions with glucose is too wasteful/destructive ATP is a much less wasteful way to transfer the necessary energy to a reaction ADP can be recharged to ATP via cellular respiration –Glucose + O2 -> CO2 + H2O + 36 ATP

Creatine Phosphate (CP) Creatine Phosphate (CP) gives up its phosphate to ADP such that ADP can be recharged into ATP Creatine supplements are popular among some athletes because they allow the potential for more ADP to be recharged

How does the body’s use of energy- storing compounds vary in different athletic events?