Topic 9- Heterotrophic Metabolism PDF

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Heterotrophic Metabolism Pi… i= inorganic Heterotrophic Metabolism Chemoheterotrophic metabolism     

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Chemical (food) is the energy source Carbon source also derived from this Figure 9.5 Electrons move through redox reactions Transfer Energy into NAD+NADH (ETC powers proton pump) o Figure 9.4  NAD + 2H (food) NADH + H Fate of carbon Oxidized to CO2 Partially oxidized to precursors o Ex. Organic acidsfermentation  Lactic acid; acetic acid; alcohols

Obligative vs. Facultative   

Obligate organism has to follow the metabolic pathway of aerobic or anaerobic o Ex. Obligate aerobic bacteria will die if exposed to O2 Facultative organism can switch metabolic pathways of aerobic or anaerobic o Ex. Yeast Overview/review o 3 major metabolic pathways  Fermentation  Glycolysis  No O2  No ETC  TEA (terminal electron acceptor) ethanol or lactic acid (facultative anaerobes. Ex. Yeast, animal cells, prokaryotes)  Anaerobic respiration  Glycolysis  No O2  ETC  TEA inorganic (ex. NO3, SO4 , obligate anaerobes. Ex. Prokaryotes)  Aerobic Respiration  Glycolysis  O2

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ETC TEA O2 (obligate anaerobes. Ex. Prokaryotes, eukaryotes)

Metabolism, the details Glycolysis 

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Note: o In cytoplasm o In all domains (very primitive) o No O2 o No CO2 Figure 9.9 Energy investment and energy payof o Energy investment phase: glucose is phosphorylated and split to 2 G3P molecules  Phosphorylation destabilizes glucose (makes it easier for the cell to break C=C bonds) o Energy payof phase  G3P pyruvate  ADPATP  Substratephosphorylation: Phosphate transferred to ADP using substrate (PEP) and an enzyme  *all ATP in glycolysis is made this way  Fig 9.7 Enzymes o Classes:  Kinases- transfer P, process of phosphorylation  Isomerase- catalyze structural rearrangement  Dehydrogenase- oxidizes substrate and transfers to an electron acceptor  Ex. NAD+  Phosphofructokinase- the ‘pacemaker’ of glycolysis or rate-limiting enzyme  Fig 9.20 Summary (fig 9.8) o Input Yield  6 carbon glucose -Pyruvate  2 ATP -2 ATP (net)  2 NAD+ -2 NADH  2Pi -2 H2O  2 ADP (net) -2 H+ o Glycolysis- Energy investment (2 ATP) to get energy payof (4 ATP, but a net of 2 ATP) o End product pyruvate (2 molecules) contains most of the energy of the original glucose

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Pyruvates can now enter other pathways:  *Fermentation  Anaerobic respiration  *Aerobic respiration

Fermentation 

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Note: o Includes glycolysis o Transfers electrons to organic molecules o Runs in cell cytoplasm o Anaerobic; NO ETC o Generates NAD+ and a TEA **CO2 is generated Regenerates NAD+needed in glycolysis Two main types: Ethanolic and Lactic acid (fig 9.18… after glycolysis) o Ethanolic: occurs in yeast cells- no O2 switch  When oxygen is present, yeast does not produce alcohol o Lactic acid: occurs in muscle cells Fermentation- alcohols and other organic acids (Ex. Candid albicans) Pros o Keeps glycolysis running o Runs when no O2 present o Product used in defence Cons o Very inefficient o 2 ATP/glucose o Poisonous to cell

Aerobic Respiration 

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Note: o 1st stage runs in cytoplasm o 2nd to 4th run in mitochondria or membrane of prokaryotes Review of mitochondrial structure (fig 6.17)

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2 membranes

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Inner membrane- prokaryote origin  Folded- cristae  Outer membrane- host cell origin o Rod shaped o Used in aerobic respiration Stage 1: Glycolysis Stage 2: Acetyl Coenzyme A (fig. 9.10) o Goes into mitochondria, carbons break of o Pyruvate is moved through the mitochondrial membrane using active transport  Entrance via porins and carriers (on inner membrane) Pyruvate Dehydrogenase= key enzyme for steps 1 to 3 (fig 9.10) 1. Oxidative decarboxylation 2. NADH formed 3. Co-A (coenzyme A)= transfer agent for acetyl a. Has the most energy that remains from the original pyruvate Stage 3: Krebs cycle (Citric acid cycle; TCA) o Where it occurs: matrix of the mitochondria o What happens: complete carbon oxidation o How it works: 8 steps, releases energy of Acetyl Co-A  Has most energy o Figure 9.11 o Get CO2, NADH, ATP, FADH2 o Note: most of energy of glucose is transferred to carriers (NADH, FADH 2)  electron shuttles carry energy of electrons to the ETC Stage 4: Electron Transport Chain o Where: inner mitochondria membrane of eukaryotes; in plasma membrane of prokaryotes o What: energy of electron is transferred in a chain of electron carriers o How: exergonic redox reactions: NADH, FADH2, feed energy into ETC to pump protons to intermembrane spaceprotons difuse back past ATP synthase to produce ATP (chemioosmosis) o Fig 10.17; 9.15 o Oxidative phohphorylation: produce ATP using energy from redox reactions of ETC Overview: Fig 9.16; 9.13 Proton pumps at 4 sites in the ETC  NADH- feeds energy to all 4 pumps  FADH2- feeds energy to 3 pumps  Energy fed in powers proton pumps Fig 9.06; 9.17 Net yields of aerobic respiration o Glycolysis: 2 ATP, 2 NADH o o

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Shuttle system: 0 to 2 ATP used Krebs cycle: 2ATP by substrate phosphorylation ETC: 26-28 ATP by oxidative phosphorylation

Prokaryotes aerobic respiration 

How does it difer vs. eukaryotesno mitochondrial membrane o Use plasma membrane instead of mitochondria o Has inner membrane, no outer membrane o

No NADH uptake(don’t need energy to pump NADH… doesn’t have to go in mitochondria because it doesn’t exist)

Efficiency of cellular metabolism of glucose  

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Complete glucose oxidation= 686kcal/mol In a lab testube: o Aerobic respiration =7.3 kcal/mol of ATP (minimum)  7.3 kcal/mol x 32 ATP = 233 kcal  233/686= 34% efficiency o Loses as heat & to transporters Estimate in the cell runs about 65% efficient (organelles or compartmentalization of reactions= controlled)

Oxidation of other nutrients (fig 9.20) 

Sort of random… Ketones- harmful byproducts- from a lot of protein o Goutfrom excess protein in diet

Requirements of aerobic respiration 

Note: (summary) o O2 acts as TEA (terminal electron acceptor) o ECT energy is linked to proton pumps o Protons flow past ATP synthase o

ADP and phosphate feed in producing ATP

Metabolic poisons  

O2 deprivation (by poison/toxin or asphyxia) o ETC is blocked (can’t remove excess electrons) Cytochrome poisons o Block or slow ETC  ex. Cyanide: binds iron in cytochrome A  *Can get cyanide in apple juice from China …apple seeds…

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Uncouplers: compounds that interfere with chemiosmosis, ETC, ATP synthase o Uncouplers mechanism(s) of activity  Open mitochondrial membrane channel  H+ bypass ATP synthase  Heat generated o Ex. DNP (2,4-dinitrophenol) o Natural uncouplers  In some cells (ex. Fat cells)  Bypass proton pumps, produce heat  Ex. Brown fat- models… normally cold, eat and then become warm  Ex. Voodoo lily o Produces heat o Use enzyme termed alternative oxidase  Uncouples ETC from all but 1 proton pump  Stapelia?  Fruit ripening  Positive feedback drives the cycle  Alternative oxidase goes up- due to an increase in ethylene gas- due to an increase in temperature  Releases aeromatic compounds Antibiotic activity o Ex. Oligomycin  Blocks ATP synthase activity in prokaryotes...