Microbiology Chapter 14: Electron Flow

How does the electron transfer system/chain carry energy?

The ETC carries energy by pumping e- and H+ ions donated by electron carriers through several cytoplasmic membrane pumps which pump them from the cytoplasm into the cytoplasmic membrane, generating an electrochemical gradient

Organotrophy

uses organic electron donors and inorganic/organic terminal electron acceptors (O2, NO3-, C4H4O4)

Lithotrophy

uses inorganic electron donors (Fe2+, H2) an inorganic/organic terminal electron acceptors (CO4, C4H4O4, etc.)

Phototrophy

involves light capture by chlorophyll, usually coupled to splitting of H2S, H2O, or organic molecules

How does the electron transport chain store the energy of the ion gradient?

The ETC stores the energy of the ion gradient through electrical potential (Δψ) or the pH difference (ΔpH), these gradients are the result of pumping electrons and H+ ions

Which forms of energy contribute to the proton motive force?

electrical potential (Δψ) and the pH difference (ΔpH) both contribute to the proton motive force

What cell processes are driven by the proton motive force?

• uptake of nutrients

• efflux of antibiotics

• flagellar movement

• synthesis of ATP

Oxidoreductases

receive a pair of e- from an organic (NADH) or inorganic (H2) molecule, coupled with Q to pump 4H+ ions across the membrane

Quinone pool (Q)

mobile electron carrier, coupled with oxidoreductases to pump 4H+ ions across the membrane

Terminal Oxidase

usually contains cytochrome, receives 2 e- from quinol (QH2)

Why would a bacteria use a metal or inorganic terminal electron receptor?

metal/inorganic terminal electron receptors are useful if the organism lives in an environment where oxygen is scarce but other materials are abundant. these receptors enable it to respire even in anaerobic conditions

Anaerobic vs. Aerobic Respiration

Anaerobic respiration uses a wide range of different terminal electron acceptors, aerobic respiration uses O2 as a terminal electron acceptor

How do bacteria benefit from producing alternative oxidoreductases?

doing so allows bacteria to conduct lithotrophy by oxidizing H2 of Fe2+, enabling them to acquire energy from inorganic electron donors

How does oxidation of inorganic minerals (lithotrophy) yield energy?

inorganic minerals are used to provide electrons to the electron transport chain, which can then be accepted by anaerobic acceptors, producing energy

How does methanogenesis affect the environment?

methanogenesis produces methane, which is a greenhouse gas, and its accumulation can contribute to global warming

Chemolithotrophy

uses inorganic electron donors and inorganic/O2 electron acceptors to preform respiration

• Helicobacter pylori

Chemoorganotrophy

uses organic electron donors and organic/inorganic/O2 electron acceptors to preform respiration

• E. coli

Methanogenesis

the process of reducing CO2 and other single carbon compounds into methane, this process is used by archaea to generate the energy needed for growth