LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane
LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 9 Cellular Respiration and Fermentation Lectures by Erin Barley Kathleen Fitzpatrick 2011 Pearson Education, Inc. Harvesting stored energy Energy is stored in organic molecules carbohydrates, fats, proteins
Heterotrophs eat these organic molecules food digest organic molecules to get raw materials for synthesis fuels for energy controlled release of energy burning fuels in a series of step-by-step enzyme-controlled reactions Figure 9.2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO2 H2O Cellular respiration in mitochondria ATP
Heat energy Organic molecules O2 ATP powers most cellular work Living economy Fueling the bodys economy eat high energy organic molecules food = carbohydrates, lipids, proteins, nucleic acids break them down digest = catabolism capture released energy in a form the cell can use Need an energy currency
a way to pass energy around need a short term energy storage molecule Whoa! Hot stuff! ATP ATP Adenosine TriPhosphate modified nucleotide nucleotide = adenine + ribose + Pi AMP AMP + Pi ADP ADP + Pi ATP adding phosphates is endergonic How efficient! Build once, use many ways
high energy bonds How does ATP store energy? AMP ADP ATP I think hes a bit unstable dont you? O O O OP O P OP OP O
O O O Each negative PO4 more difficult to add a lot of stored energy in each bond most energy stored in 3rd Pi 3rd Pi is hardest group to keep bonded to molecule Bonding of negative Pi groups is unstable spring-loaded Pi groups pop off easily & release energy Instability of its P bonds makes ATP an excellent energy donor How does ATP transfer energy? ADP ATP O O O
OP OP OP O O O O O OP O + O ATP ADP releases energy G = -7.3 kcal/mole Fuel other reactions Phosphorylation released Pi can transfer to other molecules destabilizing the other molecules enzyme that phosphorylates = kinase 7.3
energy ATP / ADP cycle Cant store ATP good energy donor, cellular not good energy storage respiration ATP 7.3 kcal/mole too reactive transfers Pi too easily only short term energy ADP + Pi storage carbohydrates & fats are A working muscle recycles over long term energy storage 10 million ATPs per second
Whoa! Pass me the glucose (and O2)! How do we harvest energy from fuels? Digest large molecules into smaller ones break bonds & move electrons from one molecule to another as electrons move they carry energy with them that energy is stored in another bond, released as heat or harvested to make ATP loses e- gains e- + e- oxidized
reduced + + eoxidation ereduction redox Coupling oxidation & reduction REDOX reactions in respiration release energy as breakdown organic molecules break C-C bonds strip off electrons from C-H bonds by removing H atoms C6H12O6 CO2 = the fuel has been oxidized
electrons attracted to more electronegative atoms in biology, the most electronegative atom? O2 H2O = oxygen has been reduced O couple REDOX reactions & use the released energy to synthesize ATP 2 oxidation C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction Oxidation & reduction Oxidation Reduction
adding O removing H loss of electrons releases energy exergonic removing O adding H gain of electrons stores energy endergonic oxidation C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction
Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around NAD+ NADH (reduced) FAD+2 FADH2 (reduced) NAD+ nicotinamide Vitamin B3 niacin O OP O O phosphates O
OP O O NADH O H C N+ + adenine ribose sugar H H O
NH2 H C reduction O OP O oxidation O O OP O O carries electrons as a reduced molecule N+ NH
How efficient! Build once, use many ways Overview of cellular respiration 4 metabolic stages Anaerobic respiration 1. Glycolysis respiration without O2 in cytosol Aerobic respiration respiration using O2 in mitochondria 2. Pyruvate oxidation 3. Citric Acid (Krebs) cycle 4. Electron transport chain C6H12O6 +
6O2 ATP + 6H2O + 6CO2 (+ heat) Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis (splitting of sugar) breaks down glucose into two molecules of pyruvate Glycolysis occurs in the cytoplasm and has two major phases Energy investment phase Energy payoff phase Glycolysis occurs whether or not O2 is present 2011 Pearson Education, Inc. Glycolysis Breaking down glucose
glyco lysis (splitting sugar) glucose pyruvate 2x 3C 6C In the cytosol? Why does that make evolutionary sense? ancient pathway which harvests energy where energy transfer first evolved transfer energy from organic molecules to ATP still is starting point for ALL cellular respiration but its inefficient generate only 2 ATP for every 1 glucose
occurs in cytosol Thats not enough ATP for me! Evolutionary perspective Prokaryotes first cells had no organelles Enzymes of glycolysis are well-conserved Anaerobic atmosphere life on Earth first evolved without free oxygen (O2) in atmosphere energy had to be captured from organic molecules in absence of O2 Prokaryotes that evolved glycolysis are ancestors of
all modern life ALL cells still utilize glycolysis You mean were related? Do I have to invite them over for the holidays? endergonic invest some ATP exergonic harvest a little ATP & a little NADH net yield 2 ATP 2 NADH If you get boredbut you dont need to know this!!!
The Evolutionary Significance of Glycolysis Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP Glycolysis is a very ancient process 2011 Pearson Education, Inc. Concept 9.3: After pyruvate is oxidized, the citric acid cycle completes the energyyielding oxidation of organic molecules In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed 2011 Pearson Education, Inc.
The Citric Acid Cycle The citric acid cycle, also called the Krebs cycle, completes the break down of pyruvate to CO2 The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn 2011 Pearson Education, Inc. Figure 9.12-8 Acetyl CoA CoA-SH NADH H2 O
1 + H NAD 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD H2 O
Citric acid cycle 7 Fumarate NADH 3 + H CO2 CoA-SH -Ketoglutarate 6 4
CoA-SH 5 FADH2 NAD FAD Succinate GTP GDP ADP ATP Pi Succinyl CoA
NADH + H CO2 Energy accounting of Krebs cycle 4 NAD + 1 FAD 2x 4 NADH + 1 FADH2 pyruvate CO2 3C 3x 1C 1 ADP 1 ATP
ATP Net gain = 2 ATP = 8 NADH + 2 FADH2 Value of Krebs cycle? If the yield is only 2 ATP then how was the Krebs cycle an adaptation? value of NADH & FADH2 electron carriers & H carriers reduced molecules move electrons reduced molecules move H+ ions to be used in the Electron Transport Chain like $$ in the bank There is a better way!
Electron Transport Chain series of proteins built into inner mitochondrial membrane along cristae transport proteins & enzymes transport of electrons down ETC linked to pumping of H+ to create H+ gradient yields ~36 ATP from 1 glucose! only in presence of O2 (aerobic respiration) That sounds more like it! O2 Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis NADH and FADH2
account for most of the energy extracted from food They donate electrons to the electron transport chain, powers ATP synthesis via oxidative phosphorylation 2011 Pearson Education, Inc. Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins intermembrane space
fluid-filled space between membranes Oooooh! Form fits function! Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen each carrier (most are proteins except CoQ)more electronegative controlled oxidation (alternate red/ox) controlled release of energy make ATP instead of fire! Electron Transport Chain Building proton gradient!
NADH NAD+ + H e p intermembrane space H+ H+ H e- + H+ H+ C e Q e
NADH H FADH2 NAD NADH dehydrogenase + inner mitochondrial membrane e
H FAD 2H+ + cytochrome bc complex 1 O2 H2O 2 cytochrome c oxidase complex mitochondrial matrix What powers the proton (H+) pumps? Stripping H from Electron Carriers +
Electron carriers pass electrons & H to ETC H cleaved off NADH & FADH2 electrons stripped from H atoms H+ (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) flowing electrons = energy to do work transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space H H TA-DA!! Moving electrons do the work! H H +
+ H H + + H+ + + H+ + H+ H+ H + H+ H H+
C e NADH Q e FADH2 FAD NAD+ NADH dehydrogenase e
2H+ + cytochrome bc complex 1 O2 H2O 2 cytochrome c oxidase complex ADP + Pi ATP H+ But what pulls the electrons down the ETC? H 2O
O2 electrons flow downhill to O2 oxidative phosphorylation We did it! proton-motive force H+ Set up a H+ gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + Pi ATP Are we
there yet? H+ H+ H+ H+ H + H+ H+ ADP + Pi ATP H+
Chemiosmosis The diffusion of ions across a membrane build up of proton gradient (also a pH gradient) just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis So thats the point! Pyruvate from cytoplasm Inner + mitochondrial H membrane
H + Intermembrane space Electron transport C system Q NADH Acetyl-CoA 1. Electrons are harvested and carried to the transport system. NADH Krebs
cycle e- e- FADH2 to pump protons across the membrane. HO e- 2 e- 3. Oxygen joins 1 O 2 +2
2H+ with protons to form water. O2 H+ CO2 ATP Mitochondrial matrix H+ 2. Electrons provide energy ATP
ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. H+ ATP synthase Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration (Energy stored in NADH and FADH2 is used to produce ATP) 2011 Pearson Education, Inc. A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation For each molecule of glucose degraded to CO2
and water by respiration, the cell makes up to 32 molecules of ATP 2011 Pearson Education, Inc. ~4 0 Cellular respiration 2 ATP + 2 ATP + ~36 ATP
AT P Taking it beyond What is the final electron acceptor O 2 in Electron Transport Chain? H+ H+ H+ C e NADH
Q e FADH2 FAD NAD+ NADH dehydrogenase e 2H+ + cytochrome bc complex
1 O2 H2O 2 cytochrome c oxidase complex So what happens if O2 unavailable? ETC backs up nothing to pull electrons down chain NADH & FADH cant unload H 2 ATP production ceases cells run out of energy and you die! An Accounting of ATP Production by Cellular Respiration During cellular respiration, most energy flows
in this sequence: glucose NADH electron transport chain proton-motive force ATP About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32 ATP 2011 Pearson Education, Inc. Concept 9.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Most cellular respiration requires O2 to produce ATP Without O2, the electron transport chain will cease to operate In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP
2011 Pearson Education, Inc. Pyruvate is a branching point Pyruvate O2 O2 fermentation anaerobic respiration mitochondria Krebs cycle aerobic respiration AP Biology Types of Fermentation Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be
reused by glycolysis Two common types are alcohol fermentation and lactic acid fermentation 2011 Pearson Education, Inc. Alcohol Fermentation pyruvate ethanol + CO2 3C NADH 2C NAD+ back to glycolysis Dead end process at ~12% ethanol, kills yeast cant reverse the reaction Count the
carbons! AP Biology 1C bacteria yeast recycle NADH Figure 9.17a 2 ADP 2 P i Glucose 2 ATP Glycolysis
2 Pyruvate 2 NAD 2 Ethanol (a) Alcohol fermentation 2 NADH 2 H 2 CO2 2 Acetaldehyde Lactic Acid Fermentation pyruvate lactic acid 3C NADH 3C
NAD+ back to glycolysis Reversible process once O2 is available, lactate is converted back to pyruvate by the liver Count the carbons! AP Biology O2 animals some fungi recycle NADH Figure 9.17b
2 ATP 2 ADP 2 P i Glucose Glycolysis 2 NAD 2 Lactate (b) Lactic acid fermentation 2 NADH 2 H 2 Pyruvate In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce 2011 Pearson Education, Inc. Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example sulfate Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP 2011 Pearson Education, Inc. Comparing Fermentation with Anaerobic and Aerobic Respiration All use glycolysis (net ATP = 2) to oxidize glucose and harvest chemical energy of food In all three, NAD+ is the oxidizing agent that
accepts electrons during glycolysis The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule 2011 Pearson Education, Inc. Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2 Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes 2011 Pearson Education, Inc.
The Versatility of Catabolism Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration Glycolysis accepts a wide range of carbohydrates Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle 2011 Pearson Education, Inc. Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) Fatty acids are broken down by beta oxidation and yield acetyl CoA
An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate 2011 Pearson Education, Inc. Biosynthesis (Anabolic Pathways) The body uses small molecules to build other substances These small molecules may come directly from food, from glycolysis, or from the citric acid cycle 2011 Pearson Education, Inc. Regulation of Cellular Respiration via
Feedback Mechanisms Feedback inhibition is the most common mechanism for control If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway 2011 Pearson Education, Inc. Figure 9.6-3 Electrons carried via NADH and FADH2
Electrons carried via NADH Glycolysis Glucose Pyruvate CYTOSOL Pyruvate oxidation Acetyl CoA Citric acid cycle Oxidative phosphorylation:
electron transport and chemiosmosis MITOCHONDRION ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation
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