Cellular Respiration Harvesting Chemical Energy Honors Biology 2006-2007

Chemical Recycling The products of respiration are the raw materials for photosynthesis. Photosynthesis produces glucose and oxygen, the raw materials for cellular respiration. Chemical elements essential for life are recycled, but energy is not. Honors Biology 2006-2007

ATP The Point is to Make ATP! What’s the point? Honors Biology 2006-2007

Harvesting stored energy Energy is stored in organic molecules heterotrophs eat food digest organic molecules serve as raw materials for building & fuels for energy controlled release of energy series of step-by-step enzyme-controlled reactions (metabolic pathway) We eat to take in the fuels to make ATP which will then be used to help us build biomolecules and grow and move and… live! heterotrophs = “fed by others” vs. autotrophs = “self-feeders” Honors Biology 2006-2007

Harvesting energy stored in glucose Glucose is the model breakdown of glucose to produce ATP glucose + oxygen  carbon + water + energy dioxide + heat respiration C6H12O6 6O2 6CO2 6H2O ATP  + Movement of hydrogen atoms from glucose to water fuel (carbohydrates) combustion = making heat energy by burning fuels in one step respiration = making ATP (& less heat) by burning fuels in many small steps ATP glucose CO2 + H2O + heat CO2 + H2O + ATP (+ heat) Honors Biology 2006-2007

Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around There are 2 in Cellular respiration NAD+ (NADH is reduced form FAD+2 (FADH2 is reduced form) reducing power! How efficient! Build once, use many ways Nicotinamide adenine dinucleotide (NAD) — and its relative nicotinamide adenine dinucleotide phosphate (NADP) which you will meet in photosynthesis — are two of the most important coenzymes in the cell. In cells, most oxidations are accomplished by the removal of hydrogen atoms. Both of these coenzymes play crucial roles in this. Nicotinamide is also known as Vitamin B3 is believed to cause improvements in energy production due to its role as a precursor of NAD (nicotinamide adenosine dinucleotide), an important molecule involved in energy metabolism. Increasing nicotinamide concentrations increase the available NAD molecules that can take part in energy metabolism, thus increasing the amount of energy available in the cell. Vitamin B3 can be found in various meats, peanuts, and sunflower seeds. Nicotinamide is the biologically active form of niacin (also known as nicotinic acid). FAD is built from riboflavin — also known as Vitamin B2. Riboflavin is a water-soluble vitamin that is found naturally in organ meats (liver, kidney, and heart) and certain plants such as almonds, mushrooms, whole grain, soybeans, and green leafy vegetables. FAD is a coenzyme critical for the metabolism of carbohydrates, fats, and proteins into energy. Honors Biology 2006-2007

Overview of cellular respiration 3 Stages 1. Glycolysis 2. Krebs cycle 3. Electron transport chain C6H12O6 6O2 6CO2 6H2O ATP  + (+ heat) Honors Biology 2006-2007

ATP The Point is to Make ATP! What’s the point? Honors Biology 2006-2007

Glycolysis - The Gateway Breaking down glucose “glyco – lysis” (splitting sugar) occurs in cytosol Anaerobic (Does not require oxygen) inefficient production of energy glucose      pyruvate 2x 6C 3C Why does it make sense that this happens in the cytosol? Who evolved first? Honors Biology 2006-2007

Glycolysis summary Energy Investment (endergonic) invest 2 ATP Energy Yielding (exergonic) harvest 4 ATP & 2 NADH Glucose is a stable molecule it needs an activation energy to break it apart. phosphorylate it = Pi comes from ATP. make NADH & put it in the bank for later. like $$ in the bank Net Result 2 ATP 2 NADH Honors Biology 2006-2007

Pyruvate is a branching point Anaerobic respiration (fermentation) - Other organic electron acceptor Aerobic Respiration - Oxygen accepts electrons Honors Biology 2006-2007

Fermentation: Recycling NAD+? Fermentation: The recycling of NAD+ using an organic electron acceptor instead of oxygen aerobic respiration to Krebs Cycle & Electron Transport Chain in mitochondria anaerobic respiration ethanol fermentation lactic acid fermentation O2 O2 NADH which path you use depends on who you are… Honors Biology 2006-2007

Fermentation (anaerobic) Alcoholic: Bacteria, yeast 1C 3C 2C pyruvate  ethanol + CO2 NADH NAD+ to glycolysis Lactic Acid: Bacteria, fungi, human muscles Count the carbons!! Lactic acid is not a dead end like ethanol. Once you have O2 again, lactate is converted back to pyruvate by the liver and fed to the Kreb’s cycle. pyruvate  lactic acid 3C NADH NAD+ to glycolysis Honors Biology 2006-2007

Alcohol Fermentation pyruvate  ethanol + CO2 Dead end process bacteria yeast Alcohol Fermentation 1C 3C 2C pyruvate  ethanol + CO2 NADH NAD+ Dead end process Makes our beer, wine, cheeses and other food products! Count the carbons! Honors Biology 2006-2007

Lactic Acid Fermentation Bacteria fungi Lactic Acid Fermentation O2 pyruvate  lactic acid 3C  NADH NAD+ Reversible process once O2 is available, lactate is converted to pyruvate by liver Count the carbons! Honors Biology 2006-2007

ATP The Point is to Make ATP! What’s the point? Honors Biology 2006-2007

Pyruvate is a branching point Anaerobic respiration (fermentation) - Other organic electron acceptor Aerobic Respiration - Oxygen accepts electrons Honors Biology 2006-2007

Cellular respiration Honors Biology 2006-2007

Formation of Acetyl CoA The link between glycolysis and the Krebs Cycle is the change of of pyruvate to acetyl CoA. Pyruvate (3C) has to be “shortened” by one carbon so that in can enter the mitochondria It must enter the cycle as a 2 carbon molecule, Acetyl-CoA (2C). Honors Biology 2006-2007

Formation of Acetyl CoA Releases 2 CO2 (count the carbons!) Makes 2 NADH Sometimes creates 2 ATP. Acetyl CoA enters Krebs cycle where does CO2 go? [ 2x ] pyruvate    acetyl CoA + CO2 3C NAD NADH 2C 1C CO2 is fully oxidized carbon == can’t get any more energy out it CH4 is a fully reduced carbon == good fuel!!! Take a deep breath… now exhale! Honors Biology 2006-2007

Krebs cycle 1937 | 1953 aka Citric Acid Cycle Happens in mitochondria Aerobic 5 step pathway each catalyzed by specific enzyme digestion of 6C molecule Hans Krebs 1900-1981 Honors Biology 2006-2007

Count the carbons! x2 3C 2C 4C 6C 4C 6C 5C 4C 4C 4C pyruvate 3C 2C acetyl CoA citrate 4C 6C x2 4C 6C This happens twice for each glucose molecule oxidation of sugars CO2 A 2 carbon sugar went into the Krebs cycle and was taken apart completely. Two CO2 molecules were produced from that 2 carbon sugar. Glucose has now been fully oxidized! But where’s all the ATP??? 5C 4C CO2 4C 4C Honors Biology 2006-2007

Kreb’s Cycle Krebs cycle produces large quantities of electron carriers NADH FADH2 These go on to Electron Transport Chain Honors Biology 2006-2007

Energy accounting of Krebs cycle 3 NAD + 1 FAD 3 NADH + 1 FADH2 2x pyruvate          2CO2 1 ADP 1 ATP 3C ATP Net gain = 2 ATP = 6 NADH + 2 FADH2 Honors Biology 2006-2007

So why the Krebs cycle? If the yield is only 2 ATP, then why? value of NADH & FADH2 electron carriers carry energy in the form of excited electrons!!! like $$ in the bank Honors Biology 2006-2007

ATP The Point is to Make ATP! What’s the point? Honors Biology 2006-2007

ATP accounting so far… There’s got to be a better way! Glycolysis  2 ATP Kreb’s cycle  2 ATP Acetyl CoA  ~ 2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP! There’s got to be a better way! What’s the point? A working muscle recycles over 10 million ATPs per second Honors Biology 2006-2007

That sounds more like it! There is a better way! Electron Transport Chain series of molecules built into inner mitochondrial membrane transport proteins transport of electrons down ETC linked to ATP synthesis yields double-digit ATP!!!!!!!!!!!!!!!! only in presence of O2 (aerobic) O2 That sounds more like it! Honors Biology 2006-2007

Oooooh! Form fits function! Mitochondria Matrix central fluid-filled space Double membrane outer membrane inner membrane highly folded cristae fluid-filled space between membranes = intermembrane space Oooooh! Form fits function! Honors Biology 2006-2007

Time to break open the bank! Remember the NADH? Krebs cycle Glycolysis G3P 6 NADH 2 FADH2 4 NADH Time to break open the bank! Honors Biology 2006-2007

Electron Transport Chain Electron carrier pass electrons to ETC electrons passed from one electron carrier to next in mitochondrial membrane (ETC) transport proteins in membrane pump H+ across inner membrane Oxidation refers to the loss of electrons to any electron acceptor, not just to oxygen. Uses exergonic flow of electrons through ETC to pump H+ across membrane. H+ TA-DA!! NAD+ Q C NADH H2O H+ e– 2H+ + O2 FADH2 1 2 NADH dehydrogenase bc1 complex Cytochrome oxidase complex FAD ADP + Pi ATP Honors Biology 2006-2007

“proton-motive” force We did it! H+ ADP + Pi Set up a H+ gradient Allow the H+ to flow through ATP synthase Synthesizes ATP ADP + Pi  ATP ATP Are we there yet? Honors Biology 2006-2007

Electron Transport Chain Honors Biology 2006-2007

Cellular respiration + + + ~38 ATP 2 ATP ~2 ATP 2 ATP ~34 ATP Honors Biology 2006-2007

Summary of cellular respiration C6H12O6 6O2 6CO2 6H2O ~38 ATP  + Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe? Where did the glucose come from? from food eaten Where did the O2 come from? breathed in Where did the CO2 come from? oxidized carbons cleaved off of the sugars Where did the CO2 go? exhaled Where did the H2O come from? from O2 after it accepts electrons in ETC Where did the ATP come from? mostly from ETC What else is produced that is not listed in this equation? NAD, FAD, heat! Honors Biology 2006-2007