Cellular Respiration Flashcards
Substrate-level phosphorylation
Substrate (organic molecule) gives phosphate to ATP
3 steps of cellular respiration
Glycolysis
Citric acid cycle
Oxidative phosphorylation
Glycolysis
“Splitting of sugar”
Oxidation of 1 glucose molecule to 2 pyruvate molecules
Occurs in cytoplasm of cell
2 major phases: energy investment phase and energy payoff phase
Overall yield: 2 pyruvate, 2 ATP, 2 NADH
Cell’s energy
ATP (GTP)
Reduced electron carriers (NADH, FADH, NADPH)
Chemotrophy
Use of organic material for energy (source of electrons)
Fructose 1,6-bisphosphate
Non-reversible intermediate generated in glycolysis
Oxidation of glucose
6O2 + C6H12O6 -(burning)> 6CO2 + 6H2O
G=-686 kcal/mol
Fate of pyruvate
Depends on O2 availability and availability of electron transport chain
Obligate aerobes
Require O2 as electron receptor
Cannot ferment
Facultative aerobes
Can switch between anaerobic respiration and fermentation (use NO2, CO2, or SO4 as electron receptor)
Fermentation
Takes place in absence of oxygen
Use pyruvate as an electron receptor
Regenerates NAD+
Less ATP than respiration
Alcohol: glucose is transformed into ethanol (2 steps, one of which releases CO2)
Lactic acid fermentation: glucose is transformed into lactate (direct reduction)
Comparison of cellular respiration and fermentation
Both use glycolysis to oxidize glucose and other organic fuels to pyruvate
Different final electron receptor: O2 (cellular respiration), NAD+ (fermentation)
Cellular respiration produces more ATP
Conversion of pyruvate to acetyl-CoA
Occurs in mitochondria
Products of sugar and fats converted
Citric acid cycle
Takes place in mitochondrial matrix
Step 1: addition of acetyl CoA
Step 2: oxidation- CO2 lost
Step 3: regeneration of oxaloacetate
Step 1: Acetyl CoA + oxaloacetate -> citrate
Steps 2-8: Citrate -> oxaloacetate
Net result: 3 NADH, 1 GTP, 1 FADH2, -2 CO2
Biosynthetic intermediates
Glycolysis and the citric acid cycle supply them
Cell doesn’t use all of its glucose to make energy
Gluconeogenesis
Transformation of lactic acid into glucose
Used when glucose is unavailable
Glycogen
Storage form of glucose
Beta-oxidation of fatty acids
Hydrocarbons from fat -> acetyl CoA + reduced electron carriers
Occurs in mitochondria
Fat is the main storage form of energy
Mitochondrial matrix
Highly concentrated mixture of hundreds of enzymes, including those required for the oxidation of pyruvate and fatty acids and for the citric acid cycle
Inner mitochondrial membrane
Folded into cristae
Contains proteins that carry out oxidation reactions of electron transport chain and ATP synthase
Electrochemical gradient forms across
Outer mitochondrial membrane
Contains porins- permeable
Mitochondrial intermembrane space
Contains enzymes that use ATP passing out of matrix to phosphorylate other nucleotides
Protons from electron transport chain accumulate here
Chemiosmotic hypothesis
Peter Mitchell (1970s) Proton gradient that is generated by electron transport chain drives ATP synthesis
Electron transport chain
NADH dehydrogenase complex -> ubiquinone -> cytochrome b-c1 complex -> cytochrome c -> cytochrome oxidase complex -> O2
Proton pumps: NADH dehydrogenase complex, cytochrome b-c1 complex, cytochrome oxidase complex
Mobile electron carriers: ubiquinone, cytochrome c
Proton motive force
H+ gradient
Used to drive ATP synthesis, energy source for transport (mitochondria), bacterial flagellar movement
ATP synthase
Uses proton gradient to synthesize ATP
Inorganic phosphate in matrix joins to ADP: energy comes from protons turning motor
2 parts: transmembrane H+ carrier (F0), F1 ATPase
Reversible: ATP can be broken down to make H+ gradient
Total ATP yield
Cell: 30 ATP/ glucose
121: 30-36 ATP/ glucose
