Cellular Respiration PDF

Cellular Respiration  st 1 Law of Thermodynamics The total amount of energy in the universe is constant! Energy cannot be created or destroyed but only converted to one form into another! Activation Energy – Amount of E required to break chemical bonds  nd 2 La...

Cellular Respiration  st 1 Law of Thermodynamics The total amount of energy in the universe is constant! Energy cannot be created or destroyed but only converted to one form into another! Activation Energy – Amount of E required to break chemical bonds  nd 2 Law of Thermodynamics Entropy = Randomness and Chaos Universe favours Entropy – think of how messy your room gets! In all Rxns – Energy and Entropy are needed!  ENDERGONIC REACTIONS Energy of products more than reactants Photosynthesis Light energy converted to stored chemical energy C6H12O6 Every molecule of glucose contains 2870kJ Photosynthesis  EXERGONIC REACTIONS Energy of products is less than reactants Free energy is released! Cellular respiration The energy from glucose is released and harnessed into ATP at a controlled rate! Cellular Respiration  Cellular Respiration Overview ⦿ The Goal of C.R. is to create ATP from Glucose! ⦿ Four main parts... 1) Glycolysis 2) Pyruvate Oxidation 3) Krebs Cycle (Citric Acid Cycle) 4) Electron Transport Chain  Important Reactions! Redox Reactions Substrate Level Phosphorylation Oxidative Phosphorylation These rxns occur frequently throughout the cellular respiration pathways!  Redox Reactions ⦿ Energy metabolism in cells involves oxidation reactions. ⦿ Oxidation involves the transfer of an electron from a molecule, which is said to be oxidized, to another molecule, which is said to be reduced. ⦿ An oxidation cannot occur without a corresponding reduction. They are PAIRED reactions. ⦿ Many important redox reactions in cells require the presence of coenzymes. ⦿ The redox reactions of cellular respiration commonly involve the following coenzymes:  Redox Rxns Make Energy Carriers 1) NAD: Nicotinamide adenine dinucleotide NAD+ + 2 e- + 2 H+ → NADH + H+ *the second H+ dissolves into cytosol * NAD+ is reduced to form NADH. NADH is the reduced form. 2) FAD: Flavin adenine dinucleotide FAD + 2e- + 2 H+ → FADH  A Memory Trick! ⦿ LEO the lion says GER ⦿ Lose ⦿ Electrons ⦿ Oxidized! SAYS... ⦿ Gain ⦿ Electrons ⦿ Reduced!  “Reduced” means that the overall positive charge of the molecule has decreased (due to accepting the electrons!)  Oxidative Phosphorylation ATP formed in-directly Uses redox rxns (see previous slides) NADH FADH2 These molecules harvest energy and transfer it to ATP by the end of Cellular Resp.  STEP 1 - Glycolysis A glucose is broken down into 2 Pyruvate molecules Brief overview... Occurs in the cytoplasm Anaerobic (doesn’t need oxygen!)  Key Points 1- Two ATP are used to phosphorylate substrate molecules 2- 6 carbon compound Fructose 1,6 biphosphate turners into Dihydroxyacetone phosphate (DHAP) and Glyceraldhyde 3- phosphate (G3P) 3- DHAP turns into G3P 4-Inorganic phosphate is added to to G3P NAD+ is reduced to form NADH 5-ADP is converted to ATP by substrate level phosphorylation 6- The three carbon substrate molecules are rearranged and water is removed 7- ADP is converted to ATP by substrate level phosphorylation Glycolysis cont. Recall that there are 2 GAP or G3P per glucose.  Glycolysis Balance sheet for ~P bonds of ATP: ⬥ How many ATP ~P bonds expended? ________ ⬥ How many ~P bonds of ATP produced? (Remember there are two 3C fragments from glucose.) ________ ⬥ Net production of ~P bonds of ATP per glucose: ________  Overall Equation Glucose + 2 ADP + 2 Pi + 2 NAD+ 2 Pyruvate + 2 ATP + 2 (NADH + H+) Mitochondrion Anatomy  STEP 2 -Pyruvate Oxidation Occurs in the Matrix 2 Pyruvate + 2 NAD+ + 2 CoA -> 2 acetylCoA + 2 NADH + 2H+ +2CO2 Acetyl CoA then enters the Kreb Cycle!!  STEP 3 - Krebs Cycle ⦿ In mitochondria ⦿ Mostly on inner membrane ⦿ Many enzymes, coenzymes and other molecules are in an organized pattern on the inner membrane.  Krebs Steps 1- Acetyl-CoA delivers 2 C from glucose. It reacts with oxaloacetate to produce Citrate (6C) 2- Citrate undergoes 5 reactions to produce succinate. 2 oxidative rnx make CO2, while NAD+ is reduced to form NADH with each CO2 being produced 3- ATP is produced by substrate-level phosphorylation Phosphate group is added to the molecule guanosine triphosphate (GTP). Its then transferred to ADP. 4-Steps 7 to 9 are oxidation rxn. NAD+ and FAD are reduced 5- Final product is oxaloacetate.  The Balance Sheet so far... ⦿ By the end of the Krebs Cycle (thru Steps 1-3) the entire glucose molecule is consumed. ⦿ 6C get converted to 6 CO2 along the way! ⦿ HARNESSED ENERGY (NET)! › 4 ATP (2 Glycolysis, 2 Krebs) › 12 reduced coenzymes: 2 NADH (Glycolysis) 2 NADH (Pyruvate Oxidation stage) 6 NADH (Krebs) 2FADH2 (Krebs) STEP 4 – The Electron Transport Chain  ETC Details... ⦿ Occurs on the inner membrane of mito ⦿ Transports electrons (from NADH and FADH2) thru a series of redox rxns that release free energy. ⦿ This free energy is used to pump H+ protons into the inner membrane space of the mitochondria ⦿ This creates an electro-chemical gradient that is a source of free energy which is used to create ATP! The Key Structures...  The Importance of Oxygen Oxygen is the final acceptor of electrons that pass thru the ETC!! Its high electronegativity pulls the electrons through the ETC Electrons fall (like a skydiver)...this energy pumps H+ ions into the inner membrane space so they can “fall” back into the matrix and make ATP!  Chemiosmosis ⦿ Protons move through a Proton Channel and ATP synthase to produce ATP molecules ⦿ Oxidative Phosphorylation!! ⦿ Electrochemical Gradient must be maintained (by eating!) or ATP production stops!  Protons (indicated by + charge) enter back into the mitochondrial matrix through channels in ATP synthase enzyme complex. This entry is coupled to ATP synthesis from ADP and phosphate (Pi)  What happens to the NADH from Glycolysis? Electrons are delivered to NAD+ NADH passes electrons to FAD to make FADH2  NADH vs. FADH2 In simplified terms NADH pumps 3 H+ ions across...therefore creating 3 ATP molecules! FADH2 enters the ETC at Q...therefore only pumping 2 H+ ions across and making 2 ATP molecules! 2 electrons through each hydrogen pump (1 H per pump) creates 1 ATP  Aerobic Respiration Efficiency 36 to 38 ATP per glucose Proton leak through inter membrane without passing through ATP synthase complex Some protons are used to transport pryuvate molecules generated from glycolsis from the cytoplasm into the mitochondria Some energy is used to transport ATP out if the mitochondria for use in the cytoplasm  Metabolic Rate An organism’s Metabolic rate is the amount of energy consumed at a given time and a measure of the overall rate of C.R. Rxns!  Control Mechanisms Phosphofructokinase (catalyzes step 3 of Glycolysis) controls C.R. (has allosteric site) It is activated by ADP and inhibited by ATP/ Cirtate NADH inhibits pyruvate dehydrogenase and prevents Acetyl-CoA from forming Related Pathways  Protein Catabolism PRO’s Broken down into individual A.A.’s in the body. First stage of this is deamination (removal of amino group as ammonia NH3), a waste. The remaining parts of the A.A.’s are converted into components of glycolysis or Krebs cycle  Lipid Catabolism Triglycerides are digested into glycerol and fatty acids Fatty Acids are transported to the matrix, undergo beta-oxidation (conversion into acetyl CoA...enters the Kreb cycle) Anaerobic Respiration – No O2  Lactic Acid Fermentation Occurs during vigorous exercise when O2 is in short supply. Very inefficient…but quick! After glycolysis, the pyruvic acid is converted into lactic acid. L.A. is toxic and must be removed by delivering O2 to the cells…this is why you suck in wind after a sprint!!!  Lactic Acid Fermentation Elite athletes can tolerate higher L.A. levels in their blood. Eg. Lance Armstrong 4x the normal threshold! This process is also used to make cheese and yogurt…bacteria do the work!  Ethanol Fermentation Occurs in cytoplasm of yeast cells. After glycolysis, pyruvic acid is converted to CO2 and alcohol. Ethanol could be a valuable, clean burning fuel for industry and transportation.