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CELLULAR RESPIRATION

CELLULAR RESPIRATION. CHAPTER 9. Cells require energy to do work:. from outside sources. Remember:. Matter (C-H-O) is ____________. recycled. Energy is a one-way flow: Enters as __________ → leaves as ______ . heat. sunlight.

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CELLULAR RESPIRATION

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  1. CELLULAR RESPIRATION CHAPTER 9

  2. Cells require energy to do work: from outside sources Remember: Matter (C-H-O) is ____________ recycled Energy is a one-way flow: Enters as __________ → leaves as ______ heat sunlight Energy in food is contained in bonds. When bonds break (________ reaction), energy is released but not used to do work directly. Instead, what it is the energy stored as? catabolic ATP

  3. Phosphorylation: • Transfer of phosphate group(s) from ATP to • other molecules. • Causes the molecule to undergo a change • that performs work. • ATP must be re-made: _______________ • powers the synthesis of ATP. Cellular Respiration

  4. Respiration is an Oxidation-Reduction Process • Chemical reaction involving the transfer of 1 or more ___________ between reactants electrons Also called: Redox Loss of electrons (lowers energy) • Oxidation = X = reducing agent, Y = oxidizing agent Xe- + Y → X + Ye- C6H12O6 + 6O2 → 6CO2 + 6H2O • Reduction = Gain of electrons (raises energy)

  5. Sometimes electrons are not transferred • completely. The reaction simply shifts the • degree of electron sharing in a covalent bond. • Oxygen is a good oxidizing agent because: It’s very electronegative (attracts electrons) • Electrons lose potential energy when shifted to a more electronegative atom. (releases energy) • Cellular respiration releases: 686 Kcal/mole glucose

  6. Respiration is a Step-by-Step Process • Energy is released due to the change in the • covalent status of electrons as H is transferred • from ________ to ________ glucose oxygen • H transfer requires many steps. • Each step catalyzed by a co-enzyme (accepts H’s): NAD+ (nicotinamide adenine dinucleotide) • NAD+ also called: oxidizing agent; e- acceptor

  7. How NAD+ traps electrons from glucose and other foods: Enzymes called Dehydrogenases remove 2 hydrogen atoms from the substrate. sugar • Two hydrogens = 2 protons & 2 electrons • Dehydrogenase delivers: 1 proton & 2 electrons to NAD+ to convert it to NADH (reduced form) • Remaining proton is released to the • surrounding solution as: Hydrogen ion (H+) • NADH stores the electrons’ energy until it can be released through an: electron transport chain

  8. Overview of Cellular Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O+ Energy (36 net ATP) 3 Metabolic Stages: • GLYCOLYSIS: Catabolic, in cytosol, splits glucose into 2 pyruvates. • KREBS CYCLE: (Also called Citric acid cycle, or carbon pathway) Catabolic, in mitochondrial matrix, decomposes food to CO2 • ELECTRON TRANSPORT CHAIN & Oxidative Phosphorylation: inner membrane of mitochondria, transfers e- from NADH to Oxygen and H+ to make H2O and release energy to make ATP.

  9. Small Amount of ATP is made through Substrate level Phosphorylation in glycolysis & Krebs Difference? Phosphate group transferred DIRECTLY from substrate to ADP.

  10. GLYCOLYSIS: “Splitting of sugar” • 10 Step process: Uses 10 different Enzymes • No CO2 released as Glucose is oxidized to _________. pyruvate • Reactions occur in two phases: 2 ATP’s used to phosphorylate • Energy Investing: intermediates • Energy Yielding: (When the 3-Carbon intermediates are oxidized) • Per Glucose: 4 ATP (2 ATP NETGAIN!!!) 2 NADH

  11. Energy Investment Phase: • Step1)Glucose is phosphorylated by: (Hexokinase) using 1 ATP Energizes glucose: makes it more reactive. Electric charge of PO4 traps glucose in cell – WHY? Membrane blocks charged particles • Step 2) Glucose-6-phosphate is rearranged by (phosphoglucoisomerase) and converted to: • Fructose 6-phosphate

  12. Step 3) Another ATP is added by (phosphofructokinase): Sugar now has phosphate groups at each end – it’s ready to be split Step 4) Sugar splits (Aldolase) into two 3-C sugars: PGAL (glyceraldehyde phosphate) and its isomer dihydroxyacetone phosphate. Step 5) An enzyme catalyzes the conversion of a dihydroxyacetone phosphate to PGAL because the next enzyme in glycolysis is unreceptive to the isomer. • Often, it is said that step 4 splits sugar into 2 PGAL’s (simplified)

  13. Energy Yielding Phase: (Remember there are 2 PGAL’s per glucose) • Step 6) Two reactions by one enzyme (triose phosphate Dehydrogenase) • Sugar is oxidized (e- and H+ go to NAD): forms NADH, very exergonic • Phosphate group is attached to the oxidized substrate (came from inorganic phos) Step 7) Phosphate group just added is removed and joined to ADP (substrate level phosphorylation): remaining 3-phosphoglycerate is an acid (not sugar) By now 2ATP’s per glucose are made (ZERO net gain)

  14. Step 8) An Enzyme relocates the remaining phosphate group in order to: Prepare the substrate for the next reaction. Step 9) An enzyme forms a double bond in the substrate by removing H2O: Makes Phosphoenolpyruvate: (PEP) Step 10)PEP transfers a phosphate group to ADP to make ATP, remaining substance is pyruvate.What is this process called? Substrate-level phosphorylation 2 PER GLUCOSE, this step makes ___ ATPs.

  15. GLYCOLYSIS SUMMARY: 2 NAD+ Glucose 2 ATP _________________ + _____________ + _____________  ___________ + _______________ + _________________ 2NADH 4 ATP 2 Pyruvates At the End of glycolysis: • Much of the glucose energy is still left in the pyruvates • Without oxygen, this energy is WASTED (all the cell can do is fermentation). • With oxygen, __________ is transported into the ____________ where _____________ is completed. pyruvate mitochondria oxidation

  16. Pyruvate Shuttle: • As soon as pyruvate enters mitochondria, its carboxyl group (-COOH) is removed as: CO2 (Low energy -- released) and NADH (energy in the H) • Remaining 2-C acetyl group joins coenzyme A (CoA) to make it very reactive. Called: Acetyl CoA

  17. KREBS CYCLE: Also called Citric acid cycle; Carbon pathway • Discovered by: Sir Hans Krebs, 1930s • Occurs in: mitochondrial matrix (M-Compartment) • Completes __________ of organic fuel. oxidation • Removes carboxyl groups as ______ and ______ CO2 NADH • Regenerates oxaloacetate: to re-do the cycle! • 8 steps, controlled by: enzymes • Net Products per acetyl CoA (double numbers for “per glucose”): 3 NADH,1 FADH2 1 ATP,2 CO2

  18. KREBS CYCLE: Step 1) Unstable acetyl CoA bond breaks: CoA released,Acetyl group bonds 4-C oxaloacetate  6-C Citrate Step 2) Water is removed, another is added back to convert citrate to its isomer: isocitrate Step 3) Isocitrate loses CO2 and remaining 5-C is oxidized (ketoglutarate) to reduce: NAD+ to NADH Step 4) Multienzyme complex catalyzes: Removal of ______, oxidation of remaining 4-C compound to _______ NAD+ to ______, and attachment of ______ with a high energy bond to form succinyl CoA. CO2 reduce NADH CoA

  19. Step 5) Phosphate group is transferred to GDP (GTP) and then to ADP (ATP). The remaining 4-C compound is: succinate. (substrate-level phos) Step 6) Succinate is oxidized into fumarate as: 2 Hydrogens are transferred to FAD ( FADH2) Step 7) Water is added to fumarate which rearranges its bonds to become: malate Step 8) Malate is oxidized into oxaloacetate as: 1 Hydrogen is transferred to NAD+ ( NADH) Why is Step 8 “way cool”? oxaloacetate is re-generated to start over!

  20. ***Don’t Forget: For each glucose, there are 2 “turns” of the Krebs cycle: 2 ____ATP produced by ______________________ substrate level phosphorylation 6 NADH and 2 FADH2 carry many high energy electrons

  21. ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION: Electron transport chain is made of electron carrier molecules embedded in the inner mitochondrial membrane. Each successive carrier has a higher electronegativity than the carrier before it so: bits of energy are released as e- transfers. (Stored as potential energy – ATP is NOT made directly!) Except for ubiquinone(Q) the carrier molecules are proteins tightly bound to prosthetic (nonprotein) cofactors which alternate between reduced and oxidized states as they accept and donate e-.

  22. Electron transport chain: NADH transfers e- to flavin mononucleotide: (FMN) e- transferred to iron-sulfur protein: (Fe.S) e- transferred to ubiquinone: (Q) e- transferred to cytochrome b: All cytochromes have a heme (iron) group e- transferred to: (Fe.S) e- transferred to:Cyt-c1 Cyt-c Cyt-a Cyt-a3 e- finally transferred to: oxygen (1/2 O2) *FADH2 adds its electrons to the first Fe.S carrier so they: produce less ATP.

  23. As molecular O2 is reduced, it also picks up 2 protons to form water. For every __________, one ______ is reduced to ___________ molecules. O2 2 NADH’s 2 H2O The Electron transport chain does NOT produce ATP directly. It generates a _________ gradient across the inner _______________ membrane, which stores ___________ energy that can be used to ______________ ADP. proton mitochondrial potential phosphorylate

  24. Chemiosmosis: Proposed by Peter Mitchell, 1961 Explains how a H+ gradient produced during E.T.C. powers the synthesis of ATP. Site: inner mito. memb. where ATP synthase is embedded. (enzyme – helps make ATP) Hydrogens (from NADH and FADH2) are separated into H+ and e- as only the electrons are transferred through the chain. Exergonic flow of electrons pumps H+: across membrane, from matrix to the inter membrane space

  25. proton-motive force (because H+ gradient = it can do work) BOOK p. 172!!! It is an electrochemical gradient (H+ conc. and charge conc.) H+ diffuses back through the membrane: ONLY through ATP synthase ATP synthase uses H+ gradient “current” to: phosphorylate ADP and make ATP. The mechanism by which this occurs is not fully known (Perhaps YOU will discover it one day!!!)

  26. Respiratory Poisons: Inhibit cellular respiration by disrupting chemiosmosis. Cyanide: blocks e- flow to O2 during E.T.C. Oligomycin (antibiotic): inhibits ATP synthase (in bacteria) Dinitrophenol (DNP): called “uncoupler”, makes lipid bilayer leaky to H+, E.T.C. energy turns to heat, cell “burns up”

  27. Uses of Chemiosmosis: Cellular respiration: oxidative phosphorylation Photosynthesis: photophosphorylation, (light energy drives the e- flow) Bacteria: (no mitochondria), create H+ gradients across plasma membranes (pump across memb)

  28. ATP Gain during all Steps of Cellular Respiration: ATP made by direct substrate level phosphorylation: Glycolysis = Krebs cycle = 2 ATP (net) 2 ATP ATP made when chemiosmosis couples E.T.C. to oxidative phosphorylation: Maximum = 34 ATP Some energy is lost: as heat Eukaryotic cells are about 40-60% efficient (compared to cars – only 25%)

  29. Oxygen requirements: All organisms fit into one of three categories: require oxygen (us) Strict Aerobes: Strict Anaerobes: poisoned by oxygen, use respiration – sulfates or nitrates receive e- instead of O2 (some bacteria) Facultative Anaerobes: Use O2 if available

  30. Anaerobic Respiration = Fermentation (See Figure 9.17, p. 175!) Starts with glycolysis: occurs in cytosol, no O2 needed, 2 ATP gained only Steps after glycolysis do NOT yield ATP: purpose is to recycle NAD+

  31. Two main types of fermentation: Yeast ALCOHOL FERMENTATION: NADH NAD+ 2 pyruvate --------------------> 2 ethanol + 2 CO2

  32. LACTIC ACID FERMENTATION: Human Muscle, fungi, bacteria – (cheese & yogurt) NAD+ NADH 2 pyruvate --------------------> 2 lactic acid  to the liver 2 pyruvate

  33. Catabolism of other “chow”: Carbohydrates: hydrolyzed to glucose Proteins: hydrolyzed to amino acids, deamination, enter as pyruvates or later Lipids: glycerol enters ___________ (as glyceraldehyde), fatty acids enter at ____________ glycolysis acetyl CoA REMEMBER: Not all food is used for ATP, some provides carbon skeletons!

  34. Control of Respiration: Krebs cycle is controlled by ____________________. Citrate and ATP can both inhibit phosphofructokinase (glycolysis enzyme). ADP activates it. What type of enzyme is it? feedback inhibition Allosteric

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