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Law_Sherrice_B4_MM6 (Fermentation enables some cells to produce ATP…
Law_Sherrice_B4_MM6
Fermentation enables some cells to produce ATP without use of oxygen
Oxidizing agent for glycolysis is NAD+
Fermentation is extension of glycolysis to generate ATP with enough NAD+
Types of Fermentation
Glycolysis + regenerate NAD+ by transferring e- from NADH to pyruvate or derivatives of pyruvate
Alcohol fermentation (pyruvate converted to ethanol)
Release CO2 from pyruvate and converted to 2 C acetaldehyde
Acetaldehyde reduced by NADH to ethanol
Bacteria carry this out; yeast(a fungus) also uses it
Lactic acid fermentation (pyruvate reduced directly by NADH to form lactate as end product without CO2)
By fungi and bacteria make cheese and yogurt
Produce acetone and methanol
Human muscle cells make ATP by lactic acid fermentation
When sugar catabolism overpaces muscle supply of O from blood
Lactate is converted back to pyruvate by liver cells
Fermentation and Cellular Respiration Compared
Both use glycolysis to oxidize glucose and other organic fuels to pyruvate with net 2 ATP by substrate level phosphorylation
NAD+ is oxidizing agent that accepts e-s from food during glycolysis
Ferm
Final e- acceptor is organic molecule such as pyruvate or acetaldehyde
Resp
Final acceptor is O
Regenerates NAD+ but pays ATP bonus
Yields 19 times more ATP per glucose molecule
Facultative anaerobes can make enough ATP to survive using either
Muscle cells
Pyruvate
No oxygen (fermentation)
Ethanol or lactate
Oxygen (cellular respiration)
Acetyl CoA
Citric acid cycle
Serve as e- acceptor to recycle NAD+
The Evolutionary Significance of Glycolysis
Early prokaryotes may have generated ATP exclusively from glycolysis
The citric acid cycle completes the energy-yielding oxidation of organic molecules
Glycolysis release less than a quarter of chem E stored in glucose
If oxygen present, pyruvate enters mitochondrion where enzymes of CAC complete oxidation of organic fuel
Pyruvate converted to acetyl coenzyme A (acetyl CoA)
Fully oxidized and thus have little chem E and removed and given off as molecule CO2
Remaining 2 C oxidized forming acetate → e- go to NAD+ storing E in form of NADH
Coenzyme A attach to acetate by unstable bond making acetyl group very reactive
Product is acetyl CoA
Generates 1 ATP but most E is in NAD+ and related coenzyme FAD
Reduced coenzymes NADH and FADH2 move all the high E e- to ETC
Catabolic pathways yield energy by oxidizing organic fuels
Catabolic Pathways and Production of ATP
Enzymes help cell degrade complex organic molecules rich in PE to simple waste products with less energy; energy out=work or heat
catabolic=breaking down
fermentation=partial degradation of sugars that occurs without oxygen
Most efficient and prevalent is cellular respiration (mitochondria in eukaryotes)
Redox Reactions: Oxidation and Reduction
Principle of Redox
Loss of e is oxidation; gain of e is reduction
E donor=reducing agent; e acceptor=oxidizing agent
When O2 reacts with Hydrogen from methane to form water, electron of covalent bonds drawn closer to O→ each O “gained” e
Release energy when e move closer to more electro- atom
Oxidation of Organic fuel Molecules During Cellular Respiration
Hydrogen are good fuels bc energy released when e transfers to O
carbs/fats are reservoirs of e associated with hydrogen
Enzymes in cells lower Ea→ sugar oxidized
Stepwise E Harvest via NAD+ and the Electron Transport Chain
Hydrogen aren’t transferred directly to oxygen but instead are passed to coenzyme NAD+ that is an e- acceptor and acts as ox agent in respiration
Enzymes called dehydrogenases remove pair of H atoms (2p 2e) from substrate (sugar for ex)
Delivers 2 e- and 1 p to NAD+
NADH and H+
NADH molecule=stored E that can be used to make STP when e- complete their fall down an energy gradient from NADH to O2
Exergonic
E- removed from food by NADH to top higher E end of chain
At bottom lower E end, O captures these e- with H nuclei (H+) forming water
Respiration uses e- transport chain to break fall of e- to O into several releasing steps instead of one explosive reaction; transport chain built from mostly proteins into inner mitochondrion
Vs NADH→ O2 when H2 and O2 react explosively and form water
food→ NADH→ e- transport chain→ oxygen
The Stages of Cellular Respiration: A Preview
Glycolysis occurs in cytosol begins degradation process by breaking glucose into 2 molecules of a compound called pyruvate
Citric acid cycle which takes place within mitochondrial matrix completes breakdown of glucose by oxidizing derivative of pyruvate to CO2
Redox reactions when dehydrogenase enzymes transfer e- from substrates to NAD+ forming NADH
3rd stage of respiration: e- transport chain accepts e- from breakdown of products of first 2 stages → end of chain: e- are combined with molecular O and H ions forming water
ATP synthesis is oxidative phosphorylation bc powered by redox reactions of e- transport chain
90% of ATP; rest is substrate level phosphorylation (glycolysis and citric acid cycle)
Enzyme transfers phosphate group from substrate molecule to ADP
38 total ATP, 7.3 kcal/mol of free E
Inner membrane of mitochondria is site of e- transport and chemiosmosis (make up ox phos)
During oxidative phosphorylation chemiosmosis couples e- transport to ATP synthesis
The Pathway of E- Transport
Folding of inner membrane to form cristae increases surface area for space for copies of chains
Prosthetic groups (nonprotein components) bound to proteins that make up chain
NADH
Uphill: reduced so gain electron and more electro-
Downhill: oxidized so lose electron and less electro-
Passed to ubiquinone (only electron carrier that is not a protein and is small/hydrophobic)
Mobile within membrane rather than residing
Passed to cytochromes (remaining e- carriers that are proteins)
Heme group has iron atom that accepts and donates e-
Last cytochrome cyt a3 passes e-s to oxygen, very electro-
Each O atom picks up pair of H ion atoms from aqueous solution and forms water
FADH2
⅓ less energy for ATP synthesis than NADH bc lower energy level
Chemiosmosis: The E-coupling Mechanism
Protein complex ATP synthase in inner membrane of mitochondria that makes ATP to ADP and inorganic phosphate
Use E of existing ion gradient(proton/hydrogen ion) to power ATP synthesis
Difference in concentration of H+
Chemiosmosis=E stored in form of H ion gradient across membrane is used to drive cellular work like synthesis of ATP
ATP synthase: rotor in inner membrane of mitochondria, knob that protrudes matrix, internal rod extending rotor into knob, stator anchored next to rotor that holds knob stationary
ETC function is creating H+ gradient
ETC accepts and release protons H+ along with e=s
Transfer into surrounding solution sometimes (intermembrane space)
H+ gradient is proton-motive force
In mitochondria, the energy comes from exergonic redox reactions and ATP synthesis is the work formed
Chloroplasts use chemiosmosis to generate ATP during photosynthesis; light drives e- flow down ETC and resulting H+ gradient formation
Prokaryotes generate H+ gradients across plasma membranes and use proton-motive force to make ATP and pump nutrients/waste across membrane to rotate flagella
An Accounting of ATP Production by Cellular Respiration
glucose→ NADH→ ETC→ proton-motive force→ ATP
Ratio of number of NADH molecules to ATP is not whole #
1 NADH generates enough proton motive force for 2.4-3.3 ATP
FADH2 1.5-2 ATP
1 NADH=10H+ transported; 3 r 4 H+ reenter matrix via ATP synthase for 1 ATP
Different shuttles to transport e- from cytosol into mitochondrion
Use of proton motive force by redox reactions to drive other work
40% of E stored in glucose transferred to ATP; rest is heat
Glycolysis and the citric acid cycle connect to many other metabolic pathways
The Versatility of Catabolism
Starch is hydrolyzed to glucose → glycolysis
Glycogen can be hydrolyzed to glucose
Proteins can also be used for fuel
Aa must be removed (deamination)
Fats are digested to glycerol and fatty acids, glycerol is converted to intermediate of glycolysis
Beta oxidation breaks fatty acids into 2 and used as acetyl CoA in CAC
Biosynthesis (Anabolic Pathways)
Aa from hydrolysis of proteins make up own proteins
Intermediates diverted as precursors from which cell can synthesize molecule it requires
Regulation of Cellular Respiration via Feedback Mechanisms
Feedback inhibition: end product of anabolic pathway inhibits enzyme that catalyzes early step of pathway
Cell controls catabolism
Phosphofructokinase=pacemaker
Inhibited by ATP and stimulated by AMP
Enzyme active when ATP converts to AMP or ADP faster than ATP is regenerated
Glycolysis harvests chemical E by oxidizing glucose to pyruvate
Glycolysis broken down to 2 3 C sugars and oxidized to form 2 molecules of pyruvate