Lecture 17 PMB

Frage	Antworten
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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