Metabolism and Energy

Metabolic reactions & energy Some chemical reactions release energy exergonic breaking 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

Examples dehydration synthesis hydrolysis

Endergonic vs. exergonic reactions energy released energy invested G G = change in free energy = ability to do work 2005-2006

Energy & life Organisms require energy to live where does that energy come from? coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy) energy + + An exergonic reaction is coupled (paired) with an endergonic reaction so that the energy from the first can be supplied to the second. Ex: cell respiration making ATP for muscle contraction energy + +

Spontaneous reactions? If reactions are “downhill”, why don’t they just happen spontaneously? because covalent bonds are stable Why don’t polymers (carbohydrates, proteins & fats) just spontaneously digest into their monomers 2005-2006

Activation energy Breaking down large molecules requires an initial input of energy activation energy large biomolecules are stable must absorb energy to break bonds Need a spark to start a fire energy cellulose CO2 + H2O + heat

Activation energy the amount of energy needed to start the reaction. moves the reaction over an “energy hill” 2nd Law of thermodynamics Universe tends to disorder so why don’t proteins, carbohydrates & other biomolecules breakdown? at temperatures typical of the cell, molecules don’t make it over the hump of activation energy but, a cell must be metabolically active heat would speed reactions, but… would denature proteins & kill cells

Catalysts So what’s a cell to do to reduce activation energy? ENZYMES get help! … chemical help… ENZYMES Call in the... ENZYMES! G 2005-2006

Energy needs of life Organisms are endergonic systems synthesis (biomolecules) reproduction active transport movement temperature regulation Organisms are endergonic systems What do we need energy for? Which is to say… if you don’t eat, you die… because you run out of energy. The 2nd Law of Thermodynamics takes over! 2005-2006

ATP Living economy Fueling the economy Need an energy currency eat high energy organic molecules (food) break them down = catabolism (digest) capture energy in form cell can use Need an energy currency a way to pass energy around ATP Whoa! Hot stuff!

Build once, use many ways ATP Adenosine Triphosphate modified nucleotide adenine + ribose + Pi  AMP AMP + Pi  ADP ADP + Pi  ATP How efficient! Build once, use many ways an RNA nucleotide Marvel at the efficiency of biological systems! Build once = re-use over and over again. Start with a nucleotide and add phosphates to it to make this high energy molecule that drives the work of life. Let’s look at this molecule closer. Think about putting that Pi on the adenosine-ribose ==> EXERGONIC or ENDERGONIC? 2005-2006

Why does ATP store energy? Why is the 3rd phosphate like a bad boyfriend? P O– O –O P O– O –O P O– O –O P O– O –O P O– O –O Each Pi group more difficult to add a lot of stored energy in each bond most stored in 3rd Pi Phosphorylation... Storing energy with ATP Not a happy molecule Add 1st Pi  Kerplunk! Big negatively charged functional group Add 2nd Pi  EASY or DIFFICULT to add? DIFFICULT takes energy to add = same charges repel  Is it STABLE or UNSTABLE? UNSTABLE = 2 negatively charged functional groups not strongly bonded to each other So if it releases Pi  releases ENERGY Add 3rd Pi  MORE or LESS UNSTABLE? MORE = like an unstable currency • Hot stuff! • Doesn’t stick around • Can’t store it up • Dangerous to store = wants to give its Pi to anything spring-loaded 2005-2006 instability of its P bonds makes ATP an excellent energy donor

An example of Phosphorylation… Building polymers from monomers need ATP for energy & to take the water out C H OH O + H2O +4.2 kcal/mol C H OH + P ATP ADP -7.3 kcal/mol “kinase” enzyme Monomers  polymers Not that simple! H2O doesn’t just come off on its own You have to pull it off by phosphorylating monomers. Polymerization reactions (dehydration synthesis) involve a phosphorylation step! Where does the Pi come from? ATP H OH C O + P Pi -3.1 kcal/mol 2005-2006

A working muscle recycles over 10 million ATPs per second ATP / ADP cycle Can’t store ATP too reactive transfers Pi too easily only short term energy storage carbs & fats are long term energy storage Coupling of exergonic and endergonic reactions. A working muscle recycles over 10 million ATPs per second 2005-2006

“The point is to make ATP!” What’s the point? Cells spend a lot of time making ATP! “The point is to make ATP!” For chemical, mechanical, and transport work Make ATP! That’s all I do all day. And no one even notices! I didn’t HEAR you!