CH. 14 ETS & Respirations, Lithotrophy & Phototrophy Flashcards
What is the basic function of an electron transport system? What is the proton motive force?
The ETS enables a microbe to store energy as a proton motive force (promotes movement of protons across membranes downhill the electrochemical potential by ATP synthase) that is used for cellular work
How do the following differ in terms of electron donor and terminal electron acceptors:
a. Respiration
b. Lithotrophy
c. Phototrophy
Respiration:
- Electron donor -> NADH (organic)
- Electron acceptor -> oxygen or NO3 (anaerobic)
Lithotrophy:
- Electron donor -> Fe or H2 (inorganic)
- Electron acceptor -> oxygen or NO3 (anaerobic)
Phototrophy:
- Electron donor -> light energy
- Electron acceptor -> H2S, water, or carbon dioxide
What is meant by reduction potential & “redox couple”? How is reduction potential related to ∆G? How does this change when a redox reaction is reversed?
Reduction potential (E): the tendency of a molecule to accept electrons. It is proportional to ∆G, so they have opposite signs of each other
Redox couple: Combine energetically favorable couples to obtain net -∆G
When redox reactions are reversed, the sign of E changes to the opposite sign (ex. negative to positive)
Where are electron transport components of the chain located in a bacterial cell and how are they arranged? Are the components of the ETS strictly proteins?
The electron transport components are within the inner cell membrane in a bacterial cell
They are arranged by Complex I, Complex II, Coenzyme Q (ubiquinone), Complex III (cytochrome c reductase), Complex IV (cytochrome x oxidase)
They are not strictly proteins; some are made up of NADH dehydrogenase (complex I), quinone molecules, etc.
What is the theory of chemiosmosis? How does the proton motive force relate to this? What cellular processes are driven by the PMF?
Chemiosmosis is the process of diffusion of ions (usually H+ ions, protons) across a selectively permeable membrane
PMF is related to this by having differences in charges across the membrane which is used to drive ATP synthesis
What are the stages of electron transfer in the ETS? What are the components involved?
- The transfer of electrons by NADH and FADH2 to cytochrome complex I and II by redox reactions from a donor molecule to an acceptor molecule
- The establishment of an electrochemical gradient by proton pumping and movement of electrons through the chain
- Generation of ATP molecules by ATP synthase
Components:
- Functions in the membrane
- Electron transport molecules arranged in order from NEGATIVE to the POSITIVE reduction potential
- Cytochrome, non-cytochrome proteins; contain iron, sulfur, and/or copper atoms to form oxidoreductase
- Small organic cofactors
What is the role and function of the F1F0 ATP synthase?
It is a molecular machine; a multi-subunit protein
The movement of protons through the F0 subunit turns the rotor which turns the F1 subunit (the “knob”). The rotation exposes binding sites for ADP & Pi; catalyzes ADP + P into ATP
How does anaerobic respiration differ from aerobic respiration?
Aerobic respiration uses oxygen while anaerobic respiration does not. Anaerobic uses other molecules as the terminal electron acceptor (ex. NO3, SO4, etc.)
What are examples of terminal electron acceptors in
anaerobic respiration? What are these reduced to?
SO4 is a terminal electron acceptor and is reduced to hydrogen sulfide
NO3 is a terminal electron acceptor and is reduced to NO2
What is dissimilatory denitrification?
Reduced oxidized forms of nitrogen for energy
What are the different forms of nitrogen and sulfur that can be reduced as a terminal electron acceptor AND oxidized as an energy source?
Nitrogen:
- Energy source (oxidized): ammonium -> nitrite -> nitrate
- Electron acceptor (reduced): nitrate -> nitrite -> nitrous oxide -> nitrogen
Sulfur:
- Energy source (oxidized): hydrogen sulfide -> sulfur -> disulfur trioxide
- Electron acceptor (reduced): sulfate -> sulfite -> disulfur trioxide -> sulfur -> hydrogen sulfide
How does dissimilatory metal reduction differ from assimilatory metal reduction? Where are the latter types of activities found in nature?
Dissimilatory metal reduction: the reduction of metal cations and subsequent exclusion of the metal from the cell (catabolic). It is anaerobic and can be found often in lakes & wetlands
Assimilatory metal reduction: metal is incorporated into cellular components (anabolism)
What is lithotrophy? What is phototrophy?
Lithotrophy: Inorganic molecules serve as electron donors to the electron transport system (ETS)
Phototrophy: Utilizes light energy to excite electrons; the energy captured is used to power metabolism
How does sulfur metabolism by bacteria lead to corrosion?
Hydrogen sulfide can be oxidized by sulfur-oxidizing bacteria to form sulfuric acid, which corrodes steel and iron
What is hydrogenotrophy?
Hydrogen is used as the ETS electron donor (hydrogen is oxidized with a variety of electron acceptors)
It is within heterotrophs & lithotrophs - both anaerobic respirers & anaerobic lithotrophs
