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CAMPBELL & REECE CHAPTER 9.  metabolic pathways that released stored nrg by breaking down complex molecules.

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Presentation on theme: "CAMPBELL & REECE CHAPTER 9.  metabolic pathways that released stored nrg by breaking down complex molecules."— Presentation transcript:

1 CAMPBELL & REECE CHAPTER 9

2  metabolic pathways that released stored nrg by breaking down complex molecules

3  a catabolic pathway  partial degradation of sugars or other organic fuel  anaerobic  not as efficient as aerobic respiration

4  generally means aerobic  cells mostly use glucose as fuel  energy released: ATP + heat (so is exergonic)

5  nrg released:  ΔG = -686 kcal/mol [2870kJ]

6  answer based on transfer of e- during chemical reactions  moving e- releases nrg stored in organic molecules which is ultimately used to synthesize ATP

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11  substance giving away e- is called the reducing agent  substance taking e- is called the oxidizing agent

12  some do not involve complete transfer of e- (as in forming ions)

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14  *generally, organic molecules that have lots of hydrogen make excellent fuels because their bonds are source of “hilltop” e- whose nrg will be released as the e- “fall” down nrg gradient when transferred to O 2

15  H is transferred from glucose  O 2  as e- transferred nrg state of e- is lowered  that released nrg is available for ATP synthesis

16  without E A barrier, glucose or other foods would spontaneously combine with O 2 in air  body temperature not high enough to initiate combustion of glucose, enzymes required to lower E A

17  glucose & other molecules are broken down in series of steps (each w/own enzyme) key steps e- are stripped from glucose  each oxidation step involves e- traveling with H atom  NAD+  NADH  oxidized reduced  state state

18  Nicotinamide Adenine Dinucleotide  derivative of niacin

19  enzymes called dehydrogenases remove a pair of H atoms (with 2 e-) from substrate (glucose) thereby oxidizing it.  dehydrogenase then delivers the 2 e- along with 1 H (1 proton) to its coenzyme NAD+  2 nd H+ is released to surroundings

20  by receiving 2 e- & 1 H+, NAD+ loses its (+) charge  NAD+ most versatile e- acceptor in cellular respiration (used in several redox reactions)

21  When e- passed from glucose  NAD+ they lose very little of their nrg  cellular respiration uses e- transport chain to break fall of e-  O 2 into several nrg-releasing steps

22  consists of a # of molecules (proteins mostly) in inner membrane of mitochondria & plasma membrane of those prokaryotes that have aerobic respiration “top” of chain NADH carries higher nrg e- removed from glucose   “bottom” of chain lower nrg e- passed to O 2

23  e- transfer from NADH  O 2 is exergonic reaction with a free energy change of : -53 kcal/mol (-222 kJ/mol)  instead of releasing all that nrg in 1 explosive step, e- cascade down the chain from 1 carrier molecule to next in series of redox reactions  each carrier is more electronegative than previous molecule

24  O 2 is final e- acceptor because it is the most electronegative  can think of it as O 2 pulling e- down the chain in nrg-yielding tumble

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26 1. Glycolysis 2. Pyruvate Oxidation & Citric Acid Cycle 3. Oxidative Phosphorylation  e- transport chain  chemiosmosis

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28  2 parts: 1. Energy Investment Phase 2. Energy Payoff Phase

29  anaerobic  in cytoplasm  no CO 2 released  uses 2 ATP, makes 4 ATP  2 NAD+ + 4 e- + 4H+  2 NADH + 2H+  glucose  2 pyruvate + 2 H 2 O

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34  pyruvate  mitochondria via active transport (eukaryotic cells)  pyruvate  stays in cytoplasm in prokaryotes that perform aerobic respiration

35 1. Pyruvate’s carboxyl group (already oxidized so has little chemical nrg) is removed as CO 2 2. Remaining 2 C fragment is oxidized  acetate (ionized form of acetic acid) with e-  NAD+  NADH 3. CoA (derived from vit. B) attached via S atom to acetic acid  acetyl CoA

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38  aka: Krebs Cycle  tricarboxylic acid cycle  functions as metabolic furnace that oxidizes organic fuel derived from pyruvate

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41  for each acetyl group entering cycle:  3 NAD+  3NADH  1 FAD + 2 e- + 2H+  1 FADH 2  * 1 GDP + 1ATP  1GTP + 1ADP  * GTP made in many animal cell mitochondria: GTP similar to ATP in structure & function /example of substrate-level phosphorylation

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43 end of Citric Acid Cycle only have 4 ATP made (counting glycolysis)  also have NADH & FADH 2 (hi nrg e- carriers) which accounts for most of nrg extracted form glucose

44  collection of molecules embedded in inner membrane of mitochondria (prokaryotes have them embedded in their plasma membrane)  inner membrane has multiple folds allowing for multiple copies of e- transport chain to be working at same time

45  most of the molecules are proteins, rest are nonprotein components necessary for catalytic functions of certain enzymes  there is a drop in free nrg as e- move thru e- transport chain alternating reduced state  oxidized state

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47  html html  hill.com/sites/ /student_view0 /chapter25/animation__electron_transport_ system_and_formation_of_atp__quiz_1_.html hill.com/sites/ /student_view0 /chapter25/animation__electron_transport_ system_and_formation_of_atp__quiz_1_.html  s/Biology/Bio231/etc.html s/Biology/Bio231/etc.html

48  ailed-ElectronTransport-Chain ailed-ElectronTransport-Chain  c/movie-flash.htm c/movie-flash.htm

49  e- transport chain makes no ATP directly  it does break the fall of e- from food to O 2 into a series of smaller steps that releases nrg in manageable amts  for every 4 e- 1 O H+  2 H 2 O  (O 2 is final e- acceptor)

50  inner membrane protein ATP Synthase makes ADP + Pi  ATP using the proton (H+) gradient as nrg source  chemiosmosis is the process in which nrg stored in H+ gradient across membrane is used to drive cellular work (see animations)

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52  % of chemical nrg in glucose  ATP  oxidation of 1 mol glucose under standard conditions = 686 kcal/mol  1 ATP stores 7.3 kcal/mol  efficiency of cellular respiration = 7.3kcal/mol x 32mol ATP/1 mol glucose÷ 686 kcal/mol = 0.34  34%  actually a little higher: under cell conditions ΔG is lower

53  66% of nrg from oxidation of glucose lost as heat  adaptation in hibernating animals:  use brown fat: cells packed full of mitochondria & that has a protein in inner membrane that allows H+ to flow down its concentration gradient w/out making ATP (so oxidation of stored fats generates heat w/out making ATP)

54 Brown Fat

55  w/out this adaptation ATP would build up to point where cellular respiration would shut down

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57  without an adequate supply of O 2 “pulling” e- thru transport chain oxidative phosphorylation eventually stops  2 things cells can do to get some ATP out of organic fuel w/out O 2 1. Anaerobic respiration 2. Fermentation

58  uses e- transport chain (fermentation does not)  used in anaerobic bacteria:  have e- transport chain but O 2 is not the final e- acceptor  some marine prokaryotes use (SO 4 -²) sulfate ion as final e- acceptor  H 2 S

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60  uses no O 2 & no e- transport chain  is extension of glycolysis in cytoplasm that generates ATP by substrate-level phosphorylation of glycolysis & recycles NADH back to NAD+

61  Alcohol  pyruvate  ethanol in 2 steps: 1. 2 pyruvate  2 CO2 + 2 acetaldehyde 2. 2 acetaldehyde + 2 NADH  2 ethanol + 2 NAD+

62  Lactic Acid  pyruvate is reduced directly by NADH  lactate (end product)  lactate is ionized form of lactic acid  used by fungi & bacteria to make cheese & yogurt

63  all 3: 1. produce ATP by harvesting chemical nrg in food 2. use glycolysis to oxidize glucose  pyruvate with a net production of 2 ATP by substrate-level phosphorylation 3. use NAD+ as oxidizing agent

64  methods of oxidizinf NADH  NAD+ 1. Fermentation  pyruvate or acetaldehyde 2. Anaerobic Respiration  e- transport chain  atom less electronegative than O like S  H 2 S 3. Aerobic Respiration  e- transport chain  O 2  H 2 O

65  oxidative phosphorylation yields up to 16x more ATP/glucose molecule

66  only carry out fermentation or anaerobic respiration  O 2 is toxic to them

67  yeasts & many bacteria  make enough ATP to survive w/out aerobic oxidation but if O 2 available can go thru oxidative phosphorylation  muscle fibers (cells) can behave as faculative anaerobes

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70  ancient prokaryotes used glycolysis to make ATP b/4 O 2 present in atmosphere  oldest prokaryotes: 3.5 billion yrs old  2.7 billion years ago O 2 in atmosphere: source: cyanobacteria thru photosynthesis

71  Glycolysis is a metabolic “heirloom” from early cells that continues to function in fermentation & as 1 st stage in breakdown of organic molecules by respiration

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73  Glycolysis & Citric Acid Cycle lead to many other metabolic pathways  food we eat has very little glucose in it:  glycolysis can accept other carbohydrates  glycogen  breaks down to glucose  disaccharides  monosaccharides

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75  1 st broken down to their a.a.  those not needed for protein synthesis can be converted to intermediates of glycolysis & Citric Acid Cycle 1 st amino group removed (deamination)

76  1st  glycerol & fatty acids  glycerol  glyceraldehyde 3-phosphate (intermediate in glycolysis)  fatty acids  beta oxidation  2-C fragments  Citric Acid Cycle as acetyl- CoA  beta oxidation process generate NADH & FADH 2  e- transport chain (reason why lipids have more nrg stored than carbs)

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78  cpds formed as intermediaries in glycolysis & Citric Acid Cycle diverted to anabolic pathways as precursors cell uses to synthesize what it needs (using ATP in process)  a.a. (can make ~12)  pyruvate  glucose  acetyl CoA  fatty acids

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80  cells use supply & demand principles (does not synthesize more cpds than it needs)  Feedback inhibition: end product of anabolic pathway inhibits enzyme(s) that catalyze early step of pathway

81  if cell “working” harder will speed up rate of respiration  when plenty of ATP for work cell is doing production slows down  control achieved by regulating strategic places in pathway

82  enzyme in glycolysis that catalyzes addition of 2 nd phosphate group which is 1 st step that commits the substrate irreversibly to glycolytic pathway  allosteric enzyme: has receptor sites for specific inhibitors & activators

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84  inhibitor is ATP  activator: AMP  is also sensitive to concentration of citrate: when citrate builds up in mitochondria some diffuses into cytoplasm and acts as inhibitor

85  The energy that keeps us alive is released, not produced, by cellular respiration


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