Cellular Respiration Cellular Respiration is the process of converting food energy into ATP energy (i.e. the controlled release of energy from organic compounds in cells to form ATP): C 6 H 12 O O 2 6 CO H 2 O + 36 ATP The Pathway of energy in living organisms Light energy from the sun Chemical energy stored in glucose, fats, or carbohydrates Chemical energy for use in the form of ATP photosynthesis cellular respiration A Heterotroph Must Convert: To ATP in order to perform work (ATP is form of chemical energy that is usable by the cell). What is Cellular Respiration? The process of converting food energy into ATP energy because organic compounds contain stored (potential) chemical energy in their bonds (the steps of cellular respiration can be traced using glucose as an example ) C 6 H 12 O O 2 6 CO H 2 O + 36 ATP ATP is a form of chemical energy and cellular enzymes can easily make use of this energy source (when that energy is released, cells can use it for metabolism) All living organisms must perform cellular respiration (plants and animals) to get ATP. Cell Respiration Big Picture Cellular Respiration The Big Idea Glycolysis is the first step in cellular respiration Two types of cellular respiration: Aerobic (uses oxygen) and anaerobic (without oxygen) Two types of anaerobic respiration: Lactic acid fermentation (humans) and alcoholic fermentation (yeast) Glycolysis Big Picture Glycolysis Big Picture Flower Warm-up Glycolysis Big Picture consists of two major phases Big Overview of Glycolysis A closer look at the energy investment phase A closer look at the energy payoff (yielding) phase The Link Reaction - A Segue To the Mitochondrion Link Reaction Big Picture Oxidation of Pyruvate /Link Reaction When Oxygen is present, the 2 Pyruvates are translocated to the matrix of the mitochondrion where they are converted into 2 Acetyl CoA (C 2 ). Each Pyruvate releases CO 2 (decarboxylation) to form Acetate. The Acetate is oxidized and gives electrons and H + ions to 2 NAD + 2 NADH. The Acetate is combined with Coenzyme A to produce 2 Acetyl CoA molecules. Next stop is the Krebs cycle 2 NADHs carry electrons and hydrogens to the Electron Transport Chain. The Link Rxn Krebs Cycle Big Picture The Krebs Cycle Acetyl-CoA will now contribute its acetate, to the starting step of the Krebs cycle for further oxidation. During this cycle CO 2 is released Substrates are oxidized give electrons and H + ions to NAD + NADH. For each entering acetate, 3 molecules of NADH are produced. Another electron acceptor is FAD (flavin adenine dinucleotide) which is reduced to FADH2. This will also pass on electrons (like NADH) to ETC. After all the steps, the same compound (the starting point, oxaloacetate) is returned, hence a cycle. The Link Rxn The Buzz Terminology NADH Link & Krebs Oxidation Anaerobic Phosphorylation ATP Mitochondria C4 + C2 C6 C5 C4 C4 SLP CoA Matrix FADH 2 Decarboxylation What Happens to all the Reduced Coenzymes and Oxygen? NADH and FADH 2 produced earlier, go to the ETC NADH and FADH 2 release electrons to carriers/proteins embedded in the membrane of the cristae. NADH and FADH 2 (less energy) both hand over the electrons to ETC, but at different levels. As the electrons are transferred, H + ions are pumped from the matrix to the intermembrane space up the concentration gradient. Electrons are passed along a series of carriers until they are ultimately donated to an Oxygen molecule. O electrons + 2 H + (from NADH and FADH 2 ) H 2 O. The H+ diffuses down its gradient through channels provided by ATP synthases and the enzyme uses this flow to drive the oxidative phosphorylation of ADP to ATP Electron Transport Chain and Oxidative phosphorylation /ATP synthesis Cell Respiration Wrap Up The Buzz Terminology NADH Ox Phos ETCOxygen Phosphorylation ATPInner Membrane Chemiosmosis ATPase FADH 2 Proton pump Inner Membrane space cristae The account in terms of ATP output Each NADH will result in ~ 3ATPs (except for cytosol derived products), and each FADH2 in ~2 ATPs, through ETC and chemiosmosis. From glycolysisATPs 2 ATP (SLP) 2 2 NADH (ox phos) 6 (4) From Krebs cycle 8 NADH (ox phos)24 2 FADH 2 (ox phos) 4 2 ATP (SLP) 2 After ETC and Chemiosmosis38 (36) Oxidative phosphorylation will stop in the absence of electronegative oxygen that pulls electrons down the transport chain. Fermentation Overview An extension of glycolysis A process in which ATP is produced without the help of oxygen. Without the electronegative oxygen to pull electrons down the transport chain, oxidative phosphorylation ceases ATP generated soley by Substrate level phosporylation Sufficient supply of some oxidizing agent is required (usually, NAD+, which needs to be recycled). No ETC since there is no oxygen NAD+ gets recycled by use of an organic hydrogen acceptor forming lactate or ethanol. Common in prokaryotes and very useful to humans. Fermentation Factoids Two Types of Fermentation Alcoholic Fermentation Produces ethyl alcohol and CO 2 Yeast/Fungi and some prokaryotes Used to make wine and beer CO 2 released by yeast as a byproduct causes bread to rise Lactic Acid Fermentation Produces lactic acid when O 2 isnt available Animals and most bacteria A build up of lactate in your muscles from over exerting yourself and not taking in enough oxygen causes muscle fatigue (i.e.rubbery feeling) and leads to some soreness. Alcohol Fermentation Pyruvate is converted to ethanol in two steps. Alcohol fermentation by yeast is used in brewing and winemaking. Lactic Acid Fermentation Pyruvate is reduced directly by NADH to form lactate Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt The waste product, lactate, is converted back to pyruvate in the liver. The metabolism of all macromolecules is tied to cellular respiration Excess intermediates of glycolysis and the Krebs cycle can be converted to stored carbohydrates, fats and proteins. Glucose Lactate (from fermentation) Fatty acids Krebs cycle Several intermediaries used as substrates in amino acid synthesis Phospholipids Fats Pathway for synthesis of RNA, DNA Glycogen or starch Pruvate Acetyl CoA A Visual Guide to Cellular Respiration and Fermentation