 The BIG PICTURE  ATP ◦ structure, role & importance of this molecule  Importance of step-wise oxidation (through glycolysis & Krebs Cycle)  Substrate-level phosphorylation vs. oxidative phosphorylation  Electron transport chain & its link to chemiosmosis ◦ Gradient ◦ ATP synthase  Importance/role of fermentation  Evolutionary significance

 Overall Goal: ◦ Converting organic molecules [ie. sugar] into usable cellular energy [ATP]  Exchanging foreign currency  Endergonic OR exergonic reaction? ◦ Endergonic Reaction  Putting IN energy to form bonds  Remember that BONDS represent ENERGY ◦ Exergonic Reaction  Breaking bonds, RELEASING energy  Overall Equation: ◦ C 6 H 12 O 6 + O 2  CO 2 + H 2 O + ATP

 ATP is the main energy currency of the cell  Made of 3 major components: ◦ Adenine  Nitrogenous base ◦ Ribose  Sugar ◦ 3 phosphate groups  “popping off” the last phosphate group releases energy to perform cellular work

 Oxidation ◦ The LOSS of electrons  The compound becomes more POSITIVE  Reduction ◦ The GAIN of electrons  The compounds becomes more NEGATIVE ◦ WHY?  Cellular respiration is a series of oxidation/reduction reactions that uses the transfer of electrons (e - ) to perform work ◦ NB: electrons (e - ) and protons (H + ) travel together

 Organic molecules that have LOTS Of hydrogen are excellent fuels ◦ These bonds have lots of “hilltop” electrons whose energy can be released as the electrons “fall” down an energy gradient towards oxygen ◦ SLOW and STEP-WISE  Why?  Think gasoline!

 As electrons move closer to oxygen (highly electronegative), chemical energy is released that can be put to work Glucose  NADH  Electron Transport Chain  Oxygen Least electronegativeMost electronegative  Activation energy is required to start this process ◦ Enzymes help to lower this E A

 “glucose-breaking”  Occurs in the CYTOSOL  Breaks glucose (6-C) into pyruvate (3-C) ◦ Requires an investment of 2 ATP to do this  ENERGIZED  Does NOT require oxygen (anaerobic)  Diagram

 Produces 4 ATP through substrate-level phosphorylation ◦ Occurs when an enzyme transfers a phosphate group directly from a substrate molecule to ADP  ADP + P  ATP ◦ Net gain of 2 ATP  Also produces 2 NADH ◦ (electron carriers) ◦ Will go to ETC - stay tuned!

 Net Gain In Glycolysis ◦ 2 ATP -2 ATP (energy investment – to start the process) +4 ATP (substrate level phosphorylation) 2 ATP 2 NADH Electron carriers Will be used to make ATP later 2 molecules of pyruvate (3-C each) Still holds MOST of the energy in the original glucose molecule

 There are 2 pyruvate molecules (3-C each) left after glycolysis ◦ If oxygen is PRESENT, the pyruvate enters the mitochondrion ◦ The oxygen is like the “key” that unlocks the mitochondrion  Before entering the Krebs Cycle, pyruvate is converted to Acetyl CoA ◦ CO 2 is released as a waste product ◦ NADH (electron carrier) is produced ◦ Coenzyme A is added  Makes it very reactive

 The Krebs Cycle functions as a metabolic “furnace” that transfers most of the rest of the energy from Acetyl CoA (from pyruvate) to ATP, NADH, and FADH 2

 Acetyl CoA (2-C) joins with oxaloacetate (4- C) in the first step, creating citrate (6-C) ◦ Carbon dioxide is released (2 molecules) ◦ NADH is formed ◦ FADH 2 is formed ◦ ATP is formed  Substrate level phosphorylation ◦ Oxaloacetate is regenerated  CYCLE

 Yield per pyruvate molecule ◦ 4 NADH – electron carrier ◦ 1 FADH 2 – electron carrier ◦ 1 ATP  Yield per glucose molecule ◦ 8 NADH ◦ 2 FADH 2 ◦ 2 ATP  CO 2 released as a waste product

 What we REALLY need is ATP – the energy currency of the cell!  Where is most of the energy from the original glucose molecule stored? ◦ Only 4 ATP so far  2 glycolysis & 2 Krebs Cycle (both substrate-level) ◦ The energy is stored in the NADH & FADH 2 – electron carriers  The electron transport chain and chemiosmosis allow us to convert the energy in NADH & FADH 2 into ATP

 The electrons from NADH and FADH 2 are passed from one electron acceptor (cytochrome) to another ◦ Cytochromes are (mostly) proteins embedded in the inner mitochondrial membrane, folded into cristae  Why??

 Diagram:  NADH “donates” its electron at the BEGINNING of the electron chain, while FADH 2 “donates” its electron further on down the chain  Each electron acceptor (cytochrome) is more electronegative (GREEDY) than the one before it  Oxygen is the FINAL (and most electronegative) electron acceptor ◦ This forms WATER

 As electrons “fall” down the ETC, the energy they lose along the way is used to pump H + out of the mitochondrial matrix and into the intermembrane space ◦ Creates a gradient ◦ Why does this require energy?  Diagram

 As the H + come back through the membrane (to attempt to restore equilibrium), ATP synthase uses this energy to join ADP + P to form ATP ◦ ATP synthase functions like a waterwheel/turbine ◦ This is oxidative phosphorylation  Each NADH electron pumps enough protons to create 3 ATP  Because FADH 2 gives its electron further down the ETC, it can only generate 2 ATP

 Glycolysis: ◦ 2 ATP ◦ 2 NADH  4 ATP  (NADH from glycolysis makes fewer ATP than those from Krebs)  Krebs Cycle ◦ 2 ATP ◦ 8 NADH  24 ATP (ETC) ◦ 2 FADH 2  4 ATP (ETC)  Total: ◦ 6 ATP + 30 ATP  36 ATP (approx.)

 C 6 H 12 O 6 + O 2  CO 2 + H 2 O + ATP

 But what if oxygen is NOT available? ◦ Glycolysis can occur whether or not oxygen is present  2 ATP (from substrate-level phosphorylation in glycolysis) are better than 0 ◦ Fermentation (anaerobic respiration) works by allowing glycolysis to continue

 Glycolysis Review: 2 NAD + 2 NADH Glucose2 pyruvate (C-C-C-C-C-C)(C-C-C) (C-C-C) 2 ADP + P 2 ATP  BUT ◦ If you run out of NAD + to take the electrons, glycolysis would have to stop  Then, ZERO ATP would be made ◦ Fermentation solves this problem by regenerating NAD +

 Alcoholic Fermentation ◦ Occurs in PLANTS and YEAST ◦ 2 step process  Carbon dioxide is released from pyruvate (3-C), forming acetaldehyde (2- C)  Acetaldehyde is reduced by NADH (gains an electron), forming ethyl alcohol (ethanol)  NAD + is regenerated, thereby allowing glycolysis to continue ◦ Used to produce alcoholic beverages & bread

 Lactic Acid Fermentation ◦ Occurs in ANIMALS ◦ 1-step process  Pyruvate is reduced by NADH (gains an electron), forming lactic acid ◦ NAD + is regenerated, thereby allowing glycolysis to continue ◦ Occurs in muscle cells, causing muscle pain and fatigue

 The Evolutionary Significance of Glycolysis ◦ Glycolysis is the most widespread metabolic pathway ◦ Does not require oxygen ◦ Occurs in cytosol, not in membrane-bound organelles