Created by Candice Young
almost 7 years ago
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Question | Answer |
Fermentation | occurs in the absence of an electron acceptor that can be used for respiration --> partially oxidize substrate to suitable intermediate --> use electrons generated to reduce intermediate to an e- acceptor |
Key concepts behind fermentation | 1) no exogenous electron acceptor involved 2) No ETC 3) ATP generated by substrate level phosphorylation 4) Energetically inefficient, not a first choice for organisms who can respire |
why does fermentation yield much less ATP per substrate used? | because the starting compound is only PARTIALLY oxidized, and because energy rich compounds are excreted from the cell as waste |
fermentation vs respiration mechanisms of ATP synthesis | fermentation uses substrate level phosphorylation, has phosphate attached to substrate, expense of high energy waste respiration uses oxidative phosphorylation has free phosphate, expense of PMF |
What is the consequence of fermentation only yielding a small amount of ATP? | Because of this, the cell must use almost all of the carbon substrate for energy production rather than for building up biomass! |
Glycolysis | the oxidation of glucose to a pyruvate that can then be reduced to create fermentation products or fed into the citric acid cycle |
Stage 1 of glycolysis | stage that uses 2ATP/glucose, no redox reactions glucose -----> P-fructose-1,6-P |
Stage 2 of glycolysis | stage that generates 4 ATP/glucose by substrate level phosphorylation, converts 2 NAD+ to 2NADH 2 Glyceraldehyde --> 2 Pyruvate + 2 NADH |
Stage 3 of glycolysis | if respiration possible, pyruvate enters citric acid cycle before this stage can begin if not, reduction reactions make fermentation products and regenerate NAD+ at this stage Pyruvate --> Ethanol + Lactose + CO2 (dehydrogenating 2NADH in the process) |
Net energy gain from glycolysis alone | +2 ATP per cycle (low because substrate is not fully oxidized to CO2) |
The Pasteur Cycle | the change in rate of glucose consumption depending on whether bacteria are performing respiration or fermentation to see this change, try to make bacteria eat a lot of glucose without growth (deplete oxygen for example) |
Respiration mechanism | pyruvate completely oxidized to CO2 using citric acid cycle for every glucose molecule, substrate level phosphorylation produces 8 NADH, 2 FADH2, 2ATP (reduced forms of e- carriers) many intermediates of biosynthetic pathways are generated |
What is the theoretical maximum yield of ATP for an organism performing respiration? | 38 ATP per glucose much HIGHER because glucose is fully oxidized to CO2! |
Where do the electrons from NADH and FADH2 go in respiration? | the electrons go down the ETC, which generates a proton gradient that drives ATP production |
How is a proton gradient generated by respiration? | bacteria perform several small e transfers across the IM, and at each site the energy of reaction can be converted into a proton gradient (aka stored energy) if we just transferred e' directly to O acceptor --> most energy would be lost as heat! |
How do ETCs help generate ATP? | protein complexes in ETC span membrane --> some ETCs generate enough energy to pump protons from in to outside cell --> membrane becomes charged --> protons that move back in, down concentration gradient power ATP synthesis |
in what direction are electrons passed among proteins with different E0′ charges? | they are passed from LOWER to HIGHER E0' in order to release energy that is conserved as a proton gradient |
NAD+ | oxidation–reduction coenzyme "nicotinamide adenine dinucleotide" carries two H atoms (two protons, two electrons) common cytoplasmic molecule that delivers electrons from the start |
FMN | "flavin mononucleotide" intermediate electron carrier in ETC, non-covalently bound to proteins carries 2 protons and 2 electrons |
cytochrome proteins | contain covalently bound heme (porphyrin ring) cofactors has Fe coordinated at center (2+ if electron is accepted, 3+ if electron is donated) hemes are electron-only carriers diff reduction potentials depending on structure of protein |
Iron sulfur clusters | covalently bound to ETC proteins via cysteine residues Fe can be 2+ or 3+ reduction potential varies on how cluster is attached to protein and number of Fe & S |
quinones | mobile, small e- carriers that diffuse in plane of cytoplasmic membrane carry 2 e- and 2 H+ ONLY accepts e- from upstream donor (will take up proton from cytoplasm during this) passes e- on to downstream acceptor --> proton released to periplasm held in membrane by very hydrophobic R group, otherwise similar to NAD+/NADH |
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