MICR221 Lecture 9 - Respiration Without Oxygen Flashcards
what do facultative anaerobes use for respiration?
they are flexible with diverse organic/inorganic e- donors and oxygen/anaerobic e- acceptors
what is the terminal sustained mode of energy generation for respiration without oxygen?
fermentation
what do bacteria use when oxygen is limiting for respiration?
use alternative ETC configurations and bacteria use the best ETC configuration for the situation to maximise energy yields when environments change resulting in a change of the terminal electron acceptor availability
what are the 3 complexes bacteria make for terminal oxygen reduction?
complex III-IV
cytochrome bo3
cytochrome bd
what is complex III-IV?
often exists as a supercomplex with cytochrome c trapped in the complex
what is complex cytochrome bo3?
does the same job as complex III-IV as it also often exists as a supercomplex but only one complex is used and no cytochrome c is needed
what is the function of cytochrome bd?
works at low oxygen but pumps 3 fold less H+
what do pathogens and facultative anaerobes use during microaerobiosis?
cyt-bd
what are low affinity oxidases?
very inflexible with O2 not too high or too low
what are an example of low affinity oxidases?
mycobacterium leprae that cause leprosy
what is infection best on in low affinity oxidases?
best on extremities that is ideal for O2
what do both low affinity and high affinity oxidases present?
obligate aerobes that survive in low O2 and facultative anaerobes that maximise energy
what are an example of both low affinity and high affinity oxidases?
most cultured bacteria eg E.coli
what are high affinity oxidases?
don’t usually use the ETC just substrate level phosphorylation and cant help opportunists be infectious
what are anaerobic electron acceptors?
electron acceptors that are usually highly prevalent but have less of a redox potential difference therefore less energy is released
what are 2 anaerobic electron acceptors?
nitrate and fumarate
what is nitrate?
a highly prevalent nitrogen source in the environment
where is fumarate highly prevalent?
in the cell as it is a citric acid cycle intermediate but has less energy compared to nitrate
what is respiratory nitrate reductase?
a dissimilatory nitrate reduction that converts nitrate to nitrite (not directly for biomass production). It is not a proton pump but uses a redox loop to make a PMF
what does Fdn-Nar stand for?
stands for formatedehydrogenase oxidative complex
what is Fdn-Nar?
the prototypical redox loop
what is the electron carrier for Fdn-Nar?
menaquinone
what is the reductive complex for Fdn-Nar?
nitrate reductase
when is formate produced?
produced during fermentation in E coli
what increases energy gain in terms of formate?
detoxifying formate increases energy gain
what is Frd?
fumarate reductase
what is fumarate reductase?
the reverse reaction of complex II that doesn’t usually make a PMF but the PMF can come from oxidative complexes allowing for a continuation of other functions of oxidative phosphorylation
what is the last ditch option for oxidative phosphorylation?
fumarate reductase (Frd)
what are the 3 alternative roles of the electron transport chain?
redox balance
radical detoxification
protect other enzymes
what is redox balance?
maintains NADH/NAD+ to promote catabolic processes eg NDH2
what is radical detoxification?
no electron transport chain where cytochrome bd can detoxify hydrogen peroxide
what is the function of NQR?
translocates sodium
what is the function of NADH dehydrogenase?
generates a membrane potential
what is NDH2?
a type II NADH dehydrogenase involved in non-proton pumping
how i does the alternate role of the ETC protect other enzymes?
by inactivating nitrogen fixing enzymes by oxygen to use oxidases
what is proton motive force?
a chemical product of proton pumping reactions and subject to equilibrium chemistry
what is the result of a high PMF?
a high PMF shifts equilibrium to substrates therefore is no longer spontaneous and this is called back-pressure showing no need for homeostatic balance
what is the relationship between catabolic:anabolic balance and non-proton pumping ETC’s?
in terms of catabolic:anabolic balance non proton pumping electron transport chains (ETC) have increased flexibility to deal with environmental stressors when ATP demand is low
what is the result of low biomass synthesis?
low ATP demand
what is the result of increased ATP in terms of biomass synthesis?
more biomass and can cause accidental exit from persistence
what are the alternate strategies to increase ATP?
ATP hydrolysis and transporters that use H+
what determines differences in ETC configurations?
different ETC configurations are reflected in differences of central carbon metabolism due to direct (FADH2) or indirect (NADH) links to the citric acid cycle (CAC). These produce the necessary substrates or avoids them during reductive stress
what is TCA (the citric acid cycle) rerouting?
the production of NADH and FADH2
why is TCA rerouting not always desirable?
because of back pressure or the lack of a terminal electron acceptor
when are alternative pathways that avoid NADH production used?
used under hypoxia or for antibiotic persistence
e.g mycobacterium tuberculosis
what direction does rTCA operate in?
rTCA (reverse TCA cycle) operates in the reverse direction as it is reductive rather than oxidative with many enzymes replaced, especially those performing decarboxylation
why does CO2 not need photosynthesis?
because CO2 is fixed from the atmosphere without needing photosynthesis
what branches do a TCA half cycle have?
a reductive branch and an oxidative branch
what does the 2 branches of the TCA half cycle allow?
allows for the production of key precursors while fumarate is used as the terminal electron acceptor
what does the genome of the TCA half cycle typically lack?
typically lacks alpha-KG dehydrogenase or it is not expressed anaerobically
when are facultative/obligate anaerobes that are normally fermenters used?
used if there is no or limited citric acid cycle
what is the ETC used for in terms of NADH?
the ETC is used to regenerate NADH to gain extra energy and avoid toxic end products
what is the relationship between opportunistic pathogens and energy for infection?
opportunistic pathogens can use extra energy for infection
what links central carbon metabolism with electron transport chains (ETC’s)?
redox balance
what is the relationship between maintaining redox balance when ETCs fail and fermentation?
fermentation maintains redox balance when ETC’s fail but fermentation end products need to be secreted
