Electron Flow

Flashcards about electron flow in biological systems.

How do microbes transfer energy?

By moving electrons.

What does the electron transport system generate?

A proton motive force that drives protons across the membrane.

What is the function of the proton motive force (PMF)?

Stores energy to make ATP.

What is required for most energy-yielding reactions?

Transfer of electrons from a reduced electron donor to an oxidized electron acceptor.

What is the electron transport system (ETS)?

A series of membrane-soluble carriers through which electrons are transferred in aerobic respiration.

Name an alternate name for the electron transport system (ETS)

Electron transport chain (ETC)

What is the general equation for aerobic respiration?

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

What are the three major classes of prokaryotic energy-acquiring processes using an ETS?

Organotrophy, lithotrophy, and phototrophy.

What is organotrophy?

Involves organic electron donors and inorganic or organic terminal electron acceptors.

What is lithotrophy?

Involves inorganic electron donors and inorganic or organic terminal acceptors.

What is phototrophy?

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

In redox reactions, what are the DG values proportional to?

The reduction potential (E) between the oxidized form (e– acceptor) and its reduced form (e– donor).

What is reduction potential (E)?

A measure of the tendency of a molecule to accept electrons.

What type of values of E favor a reaction?

Positive values.

What does the standard reduction potential assume?

All reactants and products equal 1 M at pH 7.

Where does the ETS function?

Within a membrane.

What is the proton motive force?

The transfer of H+ through a proton pump generates an electrochemical gradient of protons

What is the function of ATP synthase?

It drives the conversion of ADP to ATP.

What is the chemiosmotic theory?

The process of the PMF driving the conversion of ADP to ATP through ATP synthase.

When protons are pumped across the membrane, how is energy stored?

In two different forms: the electrical potential and the pH difference.

What does the electrical potential arise from?

The separation of charge between the cytoplasm and solution outside the cell membrane.

What does the pH difference represent?

The log ratio of external to internal chemical concentration of H+.

What is DNP (2,4-Dinitrophenol)?

A weight loss agent with significant acute toxicity and risk of death.

Name some processes driven by the proton motive force.

Flagellar rotation, ATP formation by F1Fo ATP synthase, drug efflux pump, uniport, antiport, and symport.

What is the respiratory ETS most commonly presented?

That of the mitochondrial inner membrane.

What do NADH and FADH2 do in the mitochondrial inner membrane?

Transfer electrons ultimately to O2, producing H2O.

What do microbes use as alternative electron donors and acceptors?

A multitude of alternative electron donors and acceptors, some of which are toxic to most other organisms.

Bacillus macyae sp. nov.

An arsenate-respiring bacterium isolated from an Australian gold mine.

What does Anaeromyxobacter dehalogenans strain 2CP-C reduce?

Uranium(VI) to Uranium (IV)

What is the required electron donor for U(VI) reduction in Anaeromyxobacter dehalogenans strain 2CP-C?

Hydrogen.

What are ETS proteins called?

Oxidoreductases.

What are cytochromes?

Colored proteins whose absorbance spectrum shifts when there is a change in redox state.

What do ETS proteins such as cytochromes associate?

Electron transfer with small energy transitions, which are mediated by cofactors.

Give examples of molecular structures involved in energy transitions

Metal ions, conjugated double bonds and heteroaromatic rings

What are the three things that are required to build an ETS?

An initial substrate oxidoreductase, a mobile electron carrier, and a terminal oxidase.

List the electron acceptors from the "Electron Tower" of standard reduction potentials, from top to bottom.

CO2+4H+ + 4e-, 2H+ + 2e-, NAD++ 2H+ + 2e-, Sº + H+ + e-, CO2+2H++ 3H2 + 2e-, SO42– + 10H+ + 8e-, FAD + 2H+ + 2e-, FMN + 2H+ + 2e-, Menaquinone + 2H+ + 2e-, Fumarate + 2H+ + 2e-, Fe3+ + e-, Ubiquinone + 2H+ + 2e-, NO3– + 2H + + 2e-, NO2–+8H++ 6e-, MnO2 + 4H+ + 2e-, NO3– + 6H+ + 5e-, 1/2O2+2H+ + 2e-

List the electron donors from the "Electron Tower" of standard reduction potentials, from top to bottom.

[CH2O] glucose + H2O, H2, NADH + H+, HS-, CH4 + 2H2O, H2S+ 4H2O, FADH2, FMNH2, Menaquinol, Succinate, Fe2+(at pH 7), Ubiquinol, NO2–+ H2O, NH4+ + 2H2O, Mn2+ + 2H2O, 1/2 N2+ 3H2O, Fe2+ (at pH 2), H2O

What does the NADH:quinone oxidoreductase complex contain in the reaction centers for electron transport?

Iron-sulfur cluster [4Fe-4S] and Flavin mononucleotide (FMN).

What does the Cytochrome bo quinol oxidase complex contain in the reaction centers for electron transport?

Heme b

What do aerobic organisms use as a terminal electron acceptor?

O2

Name some prokaryotes that use terminal electron acceptors other than O2.

Metals, oxidized ions of nitrogen, and sulfur.

Where does anaerobic respiration generally occur?

In environments where oxygen is scarce.

What type of organisms usually possess alternative electron donors and electron acceptors?

Prokaryotes

What is the end product of nitrate being successively reduced?

nitrogen gas

What is the end product of sulfate being successively reduced?

hydrogen sulfide

What is lithotrophy?

The acquisition of energy by oxidation of inorganic electron donors.

What type of organisms are lithotrophs?

Bacteria or archaea

Name an example of Lithotrophy

Hydrogenotrophy

Name other electron donors and acceptors for lithotrophy

Sulfate, Iron, or Ammonia oxidation

Define Hydrogenotrophy

Use of molecular hydrogen (H2) as an electron donor

What is methanogenesis?

the reduction of CO2 and other single-carbon compounds to methane, performed only by archaea called methanogens

What does methanogenesis provide?

niches for methanotrophs, prokaryotes that oxidize methane with a TEA, such as O2, nitrate, or sulfate

What does the F1Fo ATP synthase consists of?

Fo: membrane bound Pumps protons, and F1: cytoplasmic Generates ATP

Give examples of terminal electron acceptors

Oxygen, metals, oxidized ions of nitrogen, and sulfur.

Where does anaerobic respiration generally occur?

In environments where oxygen is scarce.

which organisms are uniquely known to possess alternative electron donors and electron acceptors?

Prokaryotes

What happens when Nitrate os successively reduced?

Nitrate is successively reduced as follows: NO3 – → NO2 – → NO → 1/2 N2O → 1/2 N2

What is the result of Sulfate being successively reduced by many bacteria

Sulfate is successively reduced by many bacteria as follows: SO42– → SO32– → 1/2 S2O32– → S0 → H2S

Define Lithotrophy

Lithotrophy (or chemolithotrophy) is the acquisition of energy by oxidation of inorganic electron donors.

What oxidation causes hidden hazards for human technology, such as the corrosion of steel in underwater bridge supports?

Nitrogen oxidation

Name an example of of external corrosion

External corrosion on buried gas transmission pipeline in bog soil of Germany.

Define Hydrogenotrophy

Hydrogenotrophy is the use of molecular hydrogen (H2) as an electron donor.