Lecture 8 - Digestion, Metabolism, Carbohydrates PDF

## Lecture 8- Digestion, Metabolism, Carbohydrates ### 1. Know the structure of ATP and its uses in the cell Adenosine Triphosphate: cellular currency derived from energy source (fuel/light) * **Hydrolysis** highly exergonic due to presence of unstable bonds * **Energy** used for: *...

## Lecture 8- Digestion, Metabolism, Carbohydrates ### 1. Know the structure of ATP and its uses in the cell Adenosine Triphosphate: cellular currency derived from energy source (fuel/light) * **Hydrolysis** highly exergonic due to presence of unstable bonds * **Energy** used for: * Mechanical work * Active transport of molecules/ions * Synthesis of macromolecules * Unfavorable reaction coupling * **structure**: * Adenine * Ribose * 3 x Phosph group ### 2. Be able to recognize an oxidation-reduction reaction and determine which substance are oxidized/reduced, which are the oxidizing agent/reducing agent * **Oxidation reaction**: lose electrons, or lose hydrogen, or gain oxygen * **Reduction reaction**: gain electrons, or gain hydrogen, or lose oxygen ### 3. Know the carrier molecules discussed in this Unit and what they carry Carrier molecule: molecules used in multiple metabolic reactions to carry a molecular group or electrons * **ATP**: activated carrier of phosphoryl groups * **Activated electron carriers** derived from fuel oxidation during oxid. Phosph.: * **Nicotinamide Adenine Dinucleotide (NAD+)**: * **FAD**: * **Coenzyme A**: activated carrier of acyl groups (ex: acetyl group) ### 4. Know the enzymes that carry out digestion of complex (di, tri, poly) carbohydrates and how their breakdown products enter the glycolytic pathway **Entry of saccharides into the glycolytic pathway** * **Starch**: plants' form of stored glucose * Contains two types of glucose polymers- amylose and amylopectin * **Alpha-amylase**: enzyme present in saliva that cleaves α1-4 glycosidic bonds in starch * Generates glucose monosaccharides and maltose disaccharides * **Maltase**: cleaves maltose into glucose * Glucose from starch enters glycolysis at step 1 * **Glycogen**: storage form of glucose in animal cells * Polymer of α1-4 linked glucose subunits * α1-6 linked branch points occur every 8-12 residues * **Glycogen phosphorylase**: phosphorylates glycogen, yielding glucose 1-phosphate * **Phosphoglucomutase**: moves phosphate group from C-1 to C-6, forming G6P * **G6P** enters glycolysis at step 2 * **Galactose**: product of lactose hydrolysis * **Galactokinase**: uses ATP to phosphorylate galactose at C-1, forming galactose 1-phosphate * **G1P uridyltransferase**: uses UDP-glucose to convert galactose 1-phosphate to glucose 1-phosphate (G1P) * **Phosphoglucomutase**: moves G1P phosphate group from C-1 to C-6, forming G6P * **G6P** enters glycolysis at step 2 * **Fructose**: product of sucrose hydrolysis or enters diet via honey/fruits/corn syrup * **Most cells**: * **Hexokinase**: phosphorylates fructose to F6P * F6P enters glycolysis at step 3 * **Liver cells**: most of our fructose is processed here * **Fructokinase**: phosphorylates fructose at C-1, forming fructose 1-phosphate (F1P) * **Aldolase**: cleaves F1P into DHAP and glyceraldehyde (GA) * **Triose kinase**: phosphorylates GA at C-3, forming G3P * G3P enters glycolysis at step 5(DHAP) and 6(G3P) * The unique processing of fructose in the liver results in regulatory enzyme of PFK being bypassed * Can result in production of excess energy which may be stored as fats ### 5. Be able to identify the important characteristics of a simple sugars in their linear form and cyclic form (aldose, ketose, triose, pentose, hexose, carbonyl, hydroxyl, pyranose, furanose, a and ẞ orientation) and be able to tell the number for each carbon **Carbohydrates**: aldehydes or ketone w/ +2 hydroxyl groups (CH2O)n * **Aldose**: carbonyl group at end of carbon chain * **Ketose**: carbonyl group at any other position * **Monosaccharides**: unbranched carbon chains with one carbonyl group and multiple hydroxyl groups * Pentoses and hexoses are common but trioses also exist. * All contain +1 chiral carbon atom(s) and occur as optically active isomeric forms. * Pentoses and greater occur as cyclic structure in aq. Solution * Reaction creates new chiral center producing two stereoisomers * **a form**: new hydroxyl below ring * **ẞ form**: new hydroxyl above ring * **Pyranoses**: six-membered ring (C-6/C-2) * Can exist as chair and boat conformations * Chair is common due to less steric hinderance * **Furanoses**: five-membered ring (C-5/C-2) ### 6. Understand the terms enantiomer and epimer as regards carbohydrates * **Epimers**: two sugars that differ only in configuration around one carbon * **Enantiomers**: nonsuperimposable mirror images * Only a chiral molecule can have enantiomers * Creates D-/L- isomers ### 7. Be able to identify a glycosidic bond and label it correctly in terms of a and ẞ orientation and carbons bonded * **Glycosidic bond**: covalent linkage via condensation reaction b/t two monosaccharides * Hydroxyl group of one monosaccharide reacts with carbon of another. ### 8. Know the structures and functions of common polysaccharides from plants and animals **Polysaccharides**: sugar polymers 10+ monosac. Long * **Homopolymer**: polymer of all identical monosac. * **Glycogen**: storage form of glucose in animals * C1-C4 polymer linking glucose with C1-C6 branch points every 8-12 residues * **Starch**: storage form of glucose in plants: * Amylose and amylopectin * **Cellulose**: linear, unbranched only in plants * Linked by 1-4 glycosidic bonds * Tough, fibrous, and water-insoluble * Component of plant cell wall, most abundant polysac. * Cant be hydrolyzed by animals due to lack of enzyme * **Chitin**: N-acetyl glucosamine residues in 1-4 linkage * Second most abundant polysac. * Water-insoluble * Non-digestible by humans but possible in other mammals * Forms part of fungi' cell wall * **Heteropolymer**: different monosacc. Included * **Glycosaminoglycans**: linear polymers of repeating disaccharide units * One will have negative charge * One always N-acetylglucosamine or N-acetylgalactosamine * Provide strength, adhesiveness, and viscosity to the ECM ### 9. Know examples of carbohydrate linkage to proteins and lipids and where such carbohydrate-modified molecules may be found in cells or tissues * **Glycoproteins**: oligosaccharides covalently bound to protein * Present on outer surface of PM, blood, and organelles, and present in ECM * Differ in types of attachments: * O-linked: glycoside bond b/t carb. and OH of Ser/Thr residue * N-linked: N-glycosyl bond b.t carb and amide of Asn residue * Ex: Erythropoietin- glycoprotein secreted by kidney into blood to stimulate RBC production * **Glycolipids**: plasma membrane components where oligosacch. Act as hydrophilic head groups * **Glycosphingolipids**: contain a specific backbone structure that acts as signaling molecules in cells * **Gangliosides**: membrane lipids in euk. Cells where oligosach. containing sialic acid and other monosach act as polar head group * **Lipopolysaccharides**: present on surface of bacteria * Immune system responds to this ## Lecture 9- Glycolysis ### 10. Know the carbon and energy inputs into glycolysis, the carbon and energy outputs, the function of the two ‘stages', the overall reaction equation, the free energy change that occurs and the location where glycolysis occurs **Glycolysis**: nearly universal pathway for producing ATP by oxidizing glucose * **Occurs** within the cytoplasm * **General Process**: * **Preparatory phase**: requires ATP * 2 ATP used to active glucose to fructose 1,6-bisphosphate * Bond between C-3 and C-4 broken to yield 2 trioses * **Payoff phase**: Produces 4 ATP, 2 NADH, & 2 pyruvate (triose) * Both sugars oxidized at C-1 * Energy from oxidation conserved as NADH and ATP * **Equation**: glucose + 2NAD+ + 2ADP + 2P; → 2 pyruvate + 2NADH + 2H+ + 2ATP + 2H2O * **Is essentially irreversible** * Glucose → 2 x pyruvate ΔG´°1 = −146 kJ/mol * 2 ADP → 2 ATP ΔG′°2 = 2(30.5 kJ/mol) = 61.0 kJ/mol * **Overall** ΔG´° = −85 kJ/mol ### 11. Given a reaction from glycolysis, be able to identify the enzyme that carries out that reaction from a list of alternatives, and vice versa. Be able to intuit the chemical reaction performed by an enzyme from its name. **Prep phase**: * **Hexokinase**: phosphorylates C-6, yielding glucose 6-phosphate (G6P) * Traps glucose in the cell * Largely irreversible * Allosterically inhibited by G6P * C1 no longer in ring * Reversible reaction * **Phosphoglucose isomerase**: converts G6P to fructose 6-phosphate (F6P) * **Phosphofructokinase (PFK)**: phosphorylates C1, yielding fructose 1,6-bisphosphate(F16P) * Traps sugar as fructose * Irreversible * Rate-limiting step of glycolysis * Allosterically regulated: * ATP: inhibitor * Citrate: inhibitor * AMP: activator * **Aldolase [lyase]**- cleaves F16P at C-3/C-4 bond, yielding glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP) * Reversible * G3P can be processed to pyruvate, not DHAP * **Triose phosphate isomerase**: interconverts G3P and DHAP * Reversible * Allows DHAP to be further metabolized **Payoff phase**: everything from here on is multiplied by 2 per initial glucose molecule * **Glyceraldehyde 3-phosphate dehydrogenase (G3PDH)**- oxidizes G3P and adds phosphate, yielding 1,3-bisphopshoglycerate (1,3-BPG) * Exergonic oxidation of C1 in G3P and reduction of NAD+ to NADH * Endergonic addition of phosphate, forming 1,3-bisphosphoglycerate * Reversible * Occurs in two steps * Energy-rich thioester forms in active site of enzyme in order to link these two reactions * **Phosphoglycerate kinase**: transfers phosph. group from 1,3-BPG to ADP, forming ATP and 3-phosphoglycerate (3-PG) * Reversible * **Phosphoglycerate mutase**: shifts phosph. group from C-2 to C-3 of glycerate, forming 2-phosphoglycerate (2-PG) * Reversible * **Enolase [lyase]**: remove H2O molecule from 2-PG, producing phosphoenolpyruvate (PEP) * Reversible * PEP has high phosph.-transfer potential * **Pyruvate kinase**: transfers phosph. group from PEP to ADP, yielding ATP and pyruvate * Irreversible * Highly exergonic ### 12. Know the enzymes of glycolysis that are allosterically regulated, and in what manner that occurs Regulation of the glycolytic pathway- * **Hexokinase**: allosterically inhibited by G6P (its product) * **Phosphofructokinase (PFK)**: allosterically inhibited by ATP, allosterically activated by AMP * ATP presence lowers affinity for F6P * AMP competes with ATP for allosteric site * **Pyruvate kinase**: allosterically inhibited by ATP and alanine, stimulated by F16P (much earlier intermediate) * Example of feedforward activation ### 13. Describe the concept of phosphoryl-transfer potential. Given transfer potential data, be able to predict which molecule would transfer a phosphate group to another. **Phosphoryl-transfer potential**: standard free energy involved in hydrolysis of a phosphoryl containing compound * Used to compare the tendency of organic molecules to transfer phosph. group to an acceptor molecule * ATP has an intermediate level phosph.-transfer potential among the important phosph. molecules * Allows to function efficiently as a carrier of phosph. groups ### 14. Define substrate level phosphorylation and explain how it differs from oxidative phosphorylation; know enzymes that carry it out in glycolysis and the TCA cycle **Substrate-level phosphorylation**: formation of ATP via transfer of phosph. group from substrate to ADP * Doesn't require oxygen * Only source of ATP production in anaerobic conditions/organisms * **Glycolysis**: * **Phosphoglycerate kinase**: transfers phosph. group from 1,3-BPG to ADP, forming ATP and 3-phosphoglycerate (3-PG) * Reversible * **Pyruvate kinase**: transfers phosph. group from PEP to ADP, yielding ATP and pyruvate * Irreversible * Highly exergonic * **TCA cycle**: * **Succinyl-CoA synthetase [ligase]**: cleaves thioester bond of succinyl-CoA, forming succinate * Regenerates CoA * Intermediate, succinyl phosphate, has high phosph. transfer potential * Donates phosph. group to ADP/GDP * Forms ATP/GTP via substrate-level phosphorylation ### 15. Know the steps and enzymes in glycolysis that require ATP, generate ATP and generate NADH **Glycolysis**: * **Hexokinase**: phosphorylates C-6 using ATP, yielding glucose 6-phosphate (G6P) * Traps glucose in the cell * Largely irreversible * Allosterically inhibited by G6P * **Phosphofructokinase (PFK)**: phosphorylates C1 using ATP, yielding fructose 1,6-bisphosphate(F16P) * Traps sugar as fructose * Irreversible * Rate-limiting step of glycolysis * Allosterically regulated: * ATP: inhibitor * Citrate: inhibitor * AMP: activator * **Glyceraldehyde 3-phosphate dehydrogenase (G3PDH)**- oxidizes G3P and adds phosphate, yielding 1,3-bisphopshoglycerate (1,3-BPG) * Reversible * Occurs in two steps * Exergonic oxidation of C1 in G3P and reduction of NAD+ to NADH * Endergonic addition of phosphate, forming 1,3-bisphosphoglycerate * Energy-rich thioester forms in active site of enzyme in order to link these two reactions * **Phosphoglycerate kinase**: transfers phosph. group from 1,3-BPG to ADP, forming ATP and 3-phosphoglycerate (3-PG) * Reversible * **Pyruvate kinase**: transfers phosph. group from PEP to ADP, yielding ATP and pyruvate * Irreversible * Highly exergonic ### 16. Describes how the disaccharides lactose and sucrose are processed and how the products enter the glycolytic pathway **Lactase**: cleaves lactose into glucose and galactose * **Galactose**: product of lactose hydrolysis. * **Galactokinase**: uses ATP to phosphorylate galactose at C-1, forming galactose 1-phosphate * **G1P uridyltransferase**: uses UDP-glucose to convert galactose 1-phosphate to glucose 1-phosphate (G1P) * **Phosphoglucomutase**: moves G1P phosphate group from C-1 to C-6, forming G6P * G6P enters glycolysis at step 2 * **Sucrase**: cleaves sucrose into glucose and fructose * **Fructose**: product of sucrose hydrolysis or enters diet via honey/fruits/corn syrup * **Most cells**: * **Hexokinase**: phosphorylates fructose to F6P * F6P enters glycolysis at step 3 * **Liver cells**: most of our fructose is processed here * **Fructokinase**: phosphorylates fructose at C-1, forming fructose 1-phosphate (F1P) * **Aldolase**: cleaves F1P into DHAP and glyceraldehyde (GA) * **Triose kinase**: phosphorylates GA at C-3, forming G3P * G3P enters glycolysis at step 5(DHAP) and 6(G3P) * The unique processing of fructose in the liver results in regulatory enzyme of PFK being bypassed * Can result in production of excess energy which may be stored as fats ### 17. List the fates of pyruvate in aerobic and anaerobic situations; understand fermentation and the need for it, the two types of fermentation and their products **Fates of Pyruvate**: * **Fermentation**: anaerobic pathway for breaking down pyruvate * **Lactic acid fermentation**- * **Lactate dehydrogenase** reduces pyruvate to lactate and oxidizes NADH to NAD+ * No ATP produced * Buildup of lactate results in acidification of muscle cells and blood * Causes muscle cramps, fatigue, nausea * **Ethanol fermentation**: pyruvate catabolized to ethanol and CO2 * **Pyruvate decarboxylase**: converts pyruvate into acetaldehyde, releasing CO2 * **Alcohol dehydrogenase**: reduces acetaldehyde to ethanol and oxidizes NADH to NAD+ * **Respiration**- aerobic pathway for further oxidation of pyruvate (acetyl-CoA) * TCA cycle + ox phos. * NAD+ regenerated via ETC ## Lecture 10- TCA Cycle ### 18. Describe the structure and required cofactors of pyruvate dehydrogenase, the reactions it carries out, its role in metabolism, its substrates and products, and the mechanism by which enzyme activity is regulated **Pyruvate dehydrogenase (PDH) complex**: oxidatively decarboxylates pyruvate, forming acetyl CoA and CO2, while reducing NAD+ to NADH * **Irreversible** * Commits carbon atoms to oxidation or synthesis to fatty acids. * **Present** in the mitochondrial matrix * **Catalyzes** reaction in three steps (+ regeneration of complex): * **Decarboxylation**: CO2 released from pyruvate * E1 combines pyruvate with ionized form of TPP * Forms intermediate hydroxyethyl-TPP * CO2 liberated, leaving metabolite as 2 carbon molecule * **Oxidation of carbonyl**: produces 2 electrons * E1 oxidizes hydroxyethyl group to acetyl group * Acetyl group is transferred to LA as its disulfide bond is reduced * Forms acetyl-lipoamide which contains an (energy rich) thioester bond * TPP is regenerated * **Transfer of acetyl group to CoA**: forming acetyl CoA * E2 transfers acetyl group from acetyl-lipoamide to coenzyme A * Forms acetyl CoA * Leaves lipoamide in its reduced form: dihydrolipoamide * **Regeneration** * E3 reoxidizes dihydrolipoamide to lipoamide and reduces FAD to FADH2 * FADH2 oxidized back to FAD and NAD+ reduced to NADH * **Structure**: * E2 core consisting of 24-60 copies surrounded by variable numbers of E1 and E3. * Also consists of PDH kinase and PDH phosphatase * **Required cofactors**: * **Thiamine pyrophosphate (TPP)**: derived from vitamin B1 * **Lipoamide (LA)**: formed via attachment of lipoic acid vitamin to lysine residue on E2 * **Forms 2 NADH per glucose molecule entering glycolysis.** * **Utilizes substrate channeling**: passage of intermediates between enzymes without release. * **Regulated via Phosphorylation**: * **PDH kinase**: inhibits PDH complex via phosphorylation * Allosterically activated by products of PDH complex (ATP/NADH/Acetyl CoA) * Allosterically activated by substrates of PDH complex (ADP/NAD+/pyruvate) * **PDH phosphatase**: reverses inhibition from PDH kinase * **Summary**: * Activated by- low ATP/ADP ratio, lack of acetyl CoA * Inhibited by- high ATP/ADP and NADH/NAD+ ratios, ample fatty acids / acetyl CoA available ### 19. Know the carbon and energy inputs into the TCA cycle, the carbon and energy outputs, the function of the two ‘stages’, the overall reaction equation, and the location where the TCA cycle occurs **TCA Pathway**: harvests electrons from carbon fuels * **Summary**: * Six-carbon compound formed via condensation of acetyl group with four-carbon compound * Oxidative decarboxylation occurs twice, generating two CO2 molecules * Four-carbon compound regenerated * **Products**: (per acetyl CoA) * 2 CO2 * 3 NADH * 1 FADH2 * 1 GTP/ATP * **Steps**: * **Oxidative Decarboxylation Phase**: capture electrons in the form of NADH * **Regeneration of Oxaloacetate**: regenerate oxaloacetate to complete cycle * **Equation**: 2 acetyl CoA + 6NAD⁺ + 2 FAD + 2ADP + 2 P → 4 CO2 + 6 NADH + 6 H+ + 2 FADH2 + 2 ATP * **Takes place** in the mt matrix ### 20. Given a reaction from the TCA cycle, be able to identify the enzyme that carries out that reaction from a list of alternatives, and vice versa. Know the steps and enzymes in the TCA cycle that generate CO2, ATP, NADH and FADH2 **Oxidative Decarboxylation Phase**: * **Citrate synthase [ligase]**: joins acetyl CoA with oxaloacetate via condensation, forming citrate * Irreversible * CoA regenerated * Exhibits induced fit * Binding of oxaloacetate creates binding site for acetyl-CoA * Acetyl-CoA binds to active site and is joined with oxaloacetate * Forms reaction intermediate, citryl CoA. * Causes enzyme to undergo structural change * Citryl CoA cleaved to form citrate and coenzyme A * **Aconitase [isomerase]**: rearranges citrate, forming isocitrate * Reversible * Endergonic, requires flux through pathway to pull reaction forward * Formation occurs through an intermediate * **Isocitrate dehydrogenase**: converts isocitrate to α-ketoglutarate via oxidative decarboxylation (CO2 released) * Irreversible * Reduces NAD+ to NADH * **α-ketoglutarate dehydrogenase complex**: converts α-ketoglutarate to succinyl-CoA via oxidative decarboxylation (CO2 released) * Irreversible * Reduces NAD+ to NADH * Oxidation energy conserved in thioester bond of succinyl-CoA * **Regeneration of Oxaloacetate** * **Succinyl-CoA synthetase [ligase]**: cleaves thioester bond of succinyl-CoA, forming succinate * Regenerates CoA * Intermediate, succinyl phosphate, has high phosph. transfer potential * Donates phosph. group to ADP/GDP * Forms ATP/GTP via substrate-level phosphorylation * **Succinate dehydrogenase**: oxidizes succinate to fumarate and reduces FAD to FADH2. * Reversible * Flavoprotein present within the IMM * Part of ETC Complex II * FADH2 generated never leaves complex, instantly sent down ETC. * **Fumarase [lyase]**: converts fumarate to L-malate via hydration * Reversible * **L-malate dehydrogenase**: oxidizes malate to oxaloacetate and reduces NAD+ to NADH * Reversible * Regenerates oxaloacetate * Highly endergonic * Rxn pulled forward via low oxaloacetate conc. ### 21. Know the enzymes of the TCA cycles that are allosterically regulated, and in what manner that occurs * **Pyruvate dehydrogenase**: controls entry of glucose * Activated by- low ATP/ADP ratio, lack of acetyl CoA * Inhibited by- high ATP/ADP and NADH/NAD+ ratios, ample fatty acids / acetyl CoA available * **PFK**: negatively regulated by citrate * Reports on status of citric acid cycle / whether carbon is needed for biosynthesis ### 22. In considering the oxidation of glucose by glycolysis and the TCA cycles, be able to identify steps that generate ATP directly versus those that generate it indirectly. Know how many ATP are generated from NADH versus FADH2 and why, and the total number of ATP generated from one glucose. Be able to predict alternate values if the system is manipulated so that certain enzymes do not function or if substrates enter at different points **ATP conversion:** | Form of Energy | ATP Conversion | Quantity | ATP produced (pyruvate) | ATP produced (glucose) | |---------------------|-----------------|----------|---------------------------|-------------------------| | ATP | 1 | 1 | 1.0 | 1 | | NADH | 2.5 | 3 | 7.5 | 15 | | FADH2 | 1.5 | 1 | 1.5 | 3 | | **TOTAL** | | | **~10** | **~20** | * **Molecule of glucose entering TCA cycle produces ~20 ATP** * **Including glycolysis: 30-32 ATP produced** ### 23. Define an anaplerotic reaction and explain the need for them **Role of TCA cycle in Anabolism**: Intermediates of TCA are also precursors for key biomolecules * Examples: heme groups, NT's, AA's, fatty acids, glucose * **Anaplerotic reactions**: replenish these intermediates * Ex: Pyruvate carboxylase: catalyzes carboxylation of pyruvate, forming oxaloacetate * Occurs in kidney, liver, brown adipose tissue * Utilizes ATP but allows TCA cycle to continue ## Lecture 11- Ox Phos: Electron Transport Chain ### 24. Know the locations where the following reactions or pathways occur: glycolysis, pyruvate dehydrogenase reaction, the TCA cycle, the electron transport chain, ATP synthesis * **Glycolysis**: cytoplasm * **PDH rxn**: matrix * **TCA cycle**: matrix * **ETC**: within the IMM * **ATP synthesis**: across the IMM, (ATP made in matrix) ### 25. Know how key reactants and products get into and exit the location where they are required, including how cytoplasmic NADH is dealt with **Mitochondrial transport**: * **Pyruvate**: * Pyruvate Crosses OMM through large pores * It then crosses the IMM via active transport by mitochondrial pyruvate carrier (MPC) * **Electron transport of Glycolytic NADH**: electrons must be moved from cytoplasm to the IMM * NADH enters OMM through porins * **Glycerol 3-phosphate (G3P) shuttle**: moves electrons from NADH to the IMM in the muscle * G3P dehydrogenase (cytoplasmic) oxidizes NADH to NAD+ and reduces DHAP to G3P. * G3P dehydrogenase (mt) then oxidizes DHAP back to G3P and reduces *FAD* to FADH2. * FADH2 then oxidizes back to *FAD* by reducing Q to QH2 within the Q pool; then taken to Complex III so electrons can enter the ETC * **Summarized electron movement**: NADH → DHAP * Inner mt membrane: G3P → FAD * Enters membrane: FADH2 → Q * Yields 1.5 ATP per NADH since Complex I is bypassed * **Malate-aspartate shuttle**: moves electrons from NADH to the IMM in the heart/liver * Cytoplasmic NADH used to generate mitochondrial NADH * Utilizes two membrane transporters. * Yields 2.5 ATP since mt NADH enters at Complex I * **Movement of ADP/ATP/P¡ across IMM**: * **Phosphate translocase (symporter)**: supplies P₁ to matrix for ATP synthesis * Uses energy from proton gradient. * Imports one phosph. group and one proton * **Adenine nucleotide translocase (antiporter)**: supplies cell with ATP and matrix with ADP * Moves ATP into intermembrane space (eventually cytoplasm) * Moves ADP into matrix * **ATP synthasome**: complex consisting of these two translocases and ATP synthase enzyme ### 26. Define oxidative phosphorylation or respiration and know which organisms do it. **Reduction/Redox Potential (E0)**: measure of a molecule's electron-transfer potential * Can be likened to the phosphate-transfer potential * Describes the tendency of a molecule to donate or accept electrons * **Value + Indication**: * **Negative E0**: strong reducing agent; readily donates electrons * Reductant is oxidized when it donates electrons * **Positive E0**: strong oxidizing agent; readily accepts electrons * Oxidant is reduced when it accepts electrons * **Electron transfer**: occurs from positive to negative **Free-energy change**: indicates how likely a redox reaction is to occur * ∆G°' = −nF∆Ε᾽。 * n = # electrons transferred * F = Faraday constant (96.48 kJ/mol*V) * ΔΕ'Ο = standard redox potential * **Free energy change from reducing oxygen to water = -220 kJ/mol** * This energy is what powers the proton gradient across the IMM ### 27. Describe the concept of reduction potential. Given reduction potential data, be able to predict which molecule would transfer electrons to another **Reduction/Redox Potential (E0)**: measure of a molecule's electron-transfer potential * Can be likened to the phosphate-transfer potential. * Describes the tendency of a molecule to donate or accept electrons * **Value + Indication**: * **Negative E0**: strong reducing agent; readily donates electrons * Reductant is oxidized when it donates electrons * **Positive E0**: strong oxidizing agent; readily accepts electrons * Oxidant is reduced when it accepts electrons * **Electron transfer**: occurs from positive to negative ### 28. Given the mathematical equation and reaction reduction potential values, be able to calculate the free energy change for a redox reaction **Free-energy change**: indicates how likely a redox reaction is to occur * ∆G°' = −nF∆Ε᾽。 * n = # electrons transferred * F = Faraday constant (96.48 kJ/mol*V) * ΔΕ'Ο = standard redox potential ### 29. Know the four complexes of the ETC (electron transport chain), the redox groups found within them, the compound each one starts (oxidizes) and ends with (reduces), and be able to describe the mobile electron carriers that move between them (ubiquinone and cytochrome c). Understand the purpose and unique role of Complex II. Know how NADH and FADH2 enter the ETC and why there is a differential in ATP payoff for the two electron carriers. **Electron-transport chain**: set of oxidation-reduction reactions that generate a proton gradient used to power ATP synthesis * **Consists of four large complexes within the IMM**: likely associated together in a supramolecular complex called the respirasome * **Complex I (NADH-Q oxidoreductase)**: pumps 4 protons per NADH (5 taken from matrix) * Electron path: NADH → FMN → Fe-S → Q * Q is reduced to QH2 and enters the Q pool * **Complex II (succinate-coenzyme Q reductase)**: no protons pumped * FADH2 generated by succinate dehydrogenase within the complex * Electron path: FADH2 → Fe-S → Q * Q is reduced to QH2 and enters the Q pool * **Complex III (Q-cyt c oxidoreductase)**: pumps 4 protons per QH2 (2 taken from matrix) * Q pool (QH2) supplies complex with electrons * Electron path: QH2 → cyt b → Fe-S → cyt c * Two cyt c are reduced; Q is re-oxidized * **Complex IV (cyt c oxidase)**: pumps 2 proton per 2(cyt c) (4 taken from matrix) * 4 molecules of cytochrome c required for oxidation reaction * Used to reduce O2 to 2(H2O) ) * 8 protons removed from matrix * 4 (chemical) protons used to reduce oxygen * 4 protons are pumped into intermembrane space * Electron path: cyt c → Cu → 02 * **Ubiquinone (Coenzyme Q10 (Q))**: transfers 2 electrons at a time * Contains long hydrophobic side chain * Allows for mobility within membrane * Accepts one electron at a time (allows for several oxidation states) * Fully oxidized: ubiquinone (Q) * Partial reduction/oxidation: intermediate (QH*) * Fully reduced: ubiquinol (QH2) * **Present within** the IMM * **Q pool**: supply of coenzyme Q within the IMM * Present at various oxidation states * **Cytochromes**: Transfers 1 electron at a time * Synthesized within the mt *