Cellular Respiration
Metabolism Cellular Metabolic Respiration Pathways: & a summary Metabolism
Bioenergetics Coupled Reactions: Bioenergetics • Flow of energy in living systems obeys: • Energy transfer from one molecule to another • 1st law of thermodynamics: couples chemical reactions – Energy can be transformed, but it cannot be created or destroyed. • Exergonic reaction: reaction releases energy • 2nd law of thermodynamics: • Endergonic reaction: reaction requires energy – Energy transformations increase entropy (degree of • Coupled bioenergetic reactions: the energy released disorganization of a system). by the exergonic reaction is used to power the – Only free energy (energy in organized state) can be used endergonic reaction. to do work. • Systems tend to go from states of higher free energy to states of lower free energy.
Cellular Respiration: ATP is the Coupled Pathways: Bioenergetics cell’s rechargable battery • Energy transfer from one metabolic pathway • Breaking down complex glucose molecule to another by means of ATP. releases energy. • Catabolic pathway (catabolism): breaking down of • That energy is used to convert ADP into macromolecules. Releases energy which may be used ATP. to produce ATP. ADP + P + energy —› ATP • Anabolic pathway (anabolism): building up of • Energy is released as ATP breaks down into macromolecules. Requires energy from ATP. ADP and AMP. • Metabolism: the balance of catabolism and anabolism in the body. ATP —› energy + ADP + P
Heyer 1 Cellular Respiration
Forward reaction is exergonic Back reaction is endergonic Coupled Metabolic Pathways: via ATP
• Cells use ATP by breaking phosphate bond and transferring energy to other compounds • Cells make ATP by transferring energy from other compounds to form phosphate bond
ATP drives endergonic reactions Cellular Metabolism • The three types of cellular work are powered by the hydrolysis of ATP • Cellular Respiration provides ATP P i • Cellular “Work” requires ATP P
Motor protein Protein moved (a) Mechanical work: ATP phosphorylates motor proteins
Membrane protein ADP ATP + P i
P P i
Solute Solute transported (b) Transport work: ATP phosphorylates transport proteins
P NH 2 NH + P Glu + 3 i Glu
Reactants: Glutamic acid Product (glutamine) and ammonia made
Figure 8.11 (c) Chemical work: ATP phosphorylates key reactants
Exergonic Oxidation of Organic Fuel
• Controlled oxidation releases energy in small, usable increments • Redox reactions regulated through Coupled reactions using ATP. reducing and oxidizing agents
Heyer 2 Cellular Respiration
Coupled Reactions: Redox Transfer of electrons is called a redox process oxidation-reduction
• AKA, Reduction–oxidation [“Redox”]
The Hindenburg explosion: Respiration: a redox process
is oxidized
C6H1206 + 6 O2 Ë 6 H20 + 6 CO2
is reduced
An exergonic redox reaction ∆G= –686 kcal/mol; \ exergonic & spontaneous
So how does the cell prevent spontaneous combustion? 2 H2+O2 2 H2O • Keep the oxidation reactions and reduction reactions separate! But the reduction of oxygen drives the oxidation of sugar!? • Couple them by means of electron shuttles.
Oxidation-Reduction (continued) Coenzymes: Electron Carriers • NAD+ (nicotinamide adenine dinucleotide) – {Derived from vitamin B : niacin} 3 - NAD+ + H+ + 2e ¤ NADH + • FADH (flavin adenine dinucleotide) – {Derived from vitamin B2: riboflavin} + + - FADH + H + 2e ¤ FADH2
• Reminder: Hydrogen = H+ + e-
Heyer 3 Cellular Respiration
Respiration Cellular Respiration vRespiration is a redox process. • Controlled oxidation of organic fuel vRespiration uses a proton gradient to power ATP (exergonic) synthesis. – coupled with vAn electron transport chain • Phosphorylation of ADP to ATP links the oxidation of food (endergonic) molecules to the production of the proton gradient.
Respiration mechanisms Preview vHarvesting electrons from food: glycolysis & the Krebs cycle. vMaking a proton gradient: electron transport chain. vUsing the proton gradient to power ATP synthesis: chemiosmosis & oxidative phosphorylation.
Cellular Respiration (making ATP) Respiration Respiration “sugar splitting”
hexokinase 1 C6 glucose Getting started Ø q“Light the match” 2 C3 pyruvates ß Spend an ATP to phorhorylate glucose ß “activated glucose” qGlucose gate is not permeable to glucose-6-phosphate ß Glucose trapped in cell
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Glycolysis summary Glycolysis v “Light two matches” to get started v Glucose partially ozixidized. v Electrons harvested, ATP made. v Pyruvate is end product.
Anaerobic Respiration Anaerobic Respiration = “fermentation”
Pyruvate Reduction Pyruvate Reduction
Fermentation pathways regenerate NAD+ & dispose of pyruvate. lactate fermentation alcohol fermentation
Heyer 5 Cellular Respiration
Aerobic Respiration
OXIDIZED Glycolysis can COENZYMES lead to
REDUCED respiration or COENZYMES fermentation
OXIDIZED COENZYMES
REDUCED COENZYMES
Pyruvate transport & oxidation to acetate Pyruvate / H+ symporter
Proton gradient drives cotransport of pyruvate & H+ into matrix
Pyruvate H+
inter- mitochondrial cytosol membrane matrix space
Aerobic Respiration Krebs Cycle
•Acetate completely oxidized to CO2 •For each acetate through the cycle: • 3 (NAD+)Æ 3 (NADH+H+)
• 1 FAD Æ 1 FADH2 • 1 ADP Æ 1ATP •(Remember, 1 glucose produced 2 acetates)
Heyer 6 Cellular Respiration
Krebs Cycle Aerobic Respiration (Citric Acid Cycle) (Tricarboxylic Acid [TCA] Cycle)
Carboxylic acid and keto acid intermediates
Respiration mechanisms Intermembrane space vHarvesting electrons from food: glycolysis & the Krebs cycle. Matrix vMaking a proton gradient: electron transport chain.
vUsing the proton gradient to Inner power ATP synthesis: membrane chemiosmosis & oxidative Outer phosphorylation. membrane
Oxidative phosphorylation: 2 parts Electron pumping protons proton gradient powers ATP synthesis Transport Chain
H+ v Series of increasingly H+ high energy e- electronegative e- + + H + carriers in 3 HH+ HH+ ATP + + membrane-bound H + H + H H ADP + P H+ H+ i complexes. H+ H+ H+ e- lower energy H+ v NADH starts at high H+ H+ H+ H+ energy level, H+ H+ proton H+ H+ H+ FADH2 slightly lower. H+ H+ H+ e- electron H+ - v O2 is the final e acceptor.
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Electron Electron transport chain & oxidative Transport Chain phosphorylation
v Each complex transports 3–4 protons for each pair of e-.
v2e- from NADH pumps 10 H+;
- 2e from FADH2 pumps only 6–7.
Respiration mechanisms
vHarvesting electrons from food: glycolysis & the Krebs cycle. ATP Synthase: vMaking a proton gradient: Facilitated electron transport chain. diffusion powers ADP vUsing the proton gradient to phosphorylation power ATP synthesis: chemiosmosis & oxidative phosphorylation.
ATP Synthase ATP Synthase v Proton gradient is electrochemical. vATP synthase v As protons move couples through ATP facilitated synthase, they turn diffusion of the rotor. + H with ATP v Active sites on knob formation. change shape, causing ADP phosphorylation. 1 ATP for 3–4 H+
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Review Yield from the electron transport chain
v Each NADH (2 e-) pumps 10 H+. + v Each FADH2 pumps 6-7 H . v 3-4 H+ Ë 1 ATP. v 1 glucose: 10 NADH Ë 25-33 ATP.
2 FADH2 Ë 3-4 ATP. about 32-34 ATP v Plus the 4 ATP from glycolysis & TCA cycle = 34–38 ATP/glucose
How much ATP would you have to eat? Aerobic Respiration
v1 mole glucose Ë 32 moles ATP. vGlucose: 180 g/mole vATP: 507 g/mole v25 g glucose = 2.3 kg ATP
Fig. 6.16 Cellular Respiration
• Anaerobic • Aerobic Respiration Respiration “with air” “without air” • = glycolysis • = glycolysis + pyruvate oxidation + pyruvate reduction + Krebs cycle + electron transport system • Produce ATP • Produces much more ATP per in absence of O2 sugar molecule • Non-toxic waste product
(CO2) • Allows use of fats and protein for fuel * { PGAL = 3PG }
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