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MICR221 Lectures 1-38 > MICR221 Lecture 9 - Respiration Without Oxygen > Flashcards

MICR221 Lecture 9 - Respiration Without Oxygen Flashcards

1
Q

what do facultative anaerobes use for respiration?

A

they are flexible with diverse organic/inorganic e- donors and oxygen/anaerobic e- acceptors

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2
Q

what is the terminal sustained mode of energy generation for respiration without oxygen?

A

fermentation

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3
Q

what do bacteria use when oxygen is limiting for respiration?

A

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

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4
Q

what are the 3 complexes bacteria make for terminal oxygen reduction?

A

complex III-IV
cytochrome bo3
cytochrome bd

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5
Q

what is complex III-IV?

A

often exists as a supercomplex with cytochrome c trapped in the complex

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6
Q

what is complex cytochrome bo3?

A

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

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7
Q

what is the function of cytochrome bd?

A

works at low oxygen but pumps 3 fold less H+

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8
Q

what do pathogens and facultative anaerobes use during microaerobiosis?

A

cyt-bd

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9
Q

what are low affinity oxidases?

A

very inflexible with O2 not too high or too low

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10
Q

what are an example of low affinity oxidases?

A

mycobacterium leprae that cause leprosy

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11
Q

what is infection best on in low affinity oxidases?

A

best on extremities that is ideal for O2

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12
Q

what do both low affinity and high affinity oxidases present?

A

obligate aerobes that survive in low O2 and facultative anaerobes that maximise energy

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13
Q

what are an example of both low affinity and high affinity oxidases?

A

most cultured bacteria eg E.coli

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14
Q

what are high affinity oxidases?

A

don’t usually use the ETC just substrate level phosphorylation and cant help opportunists be infectious

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15
Q

what are anaerobic electron acceptors?

A

electron acceptors that are usually highly prevalent but have less of a redox potential difference therefore less energy is released

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16
Q

what are 2 anaerobic electron acceptors?

A

nitrate and fumarate

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17
Q

what is nitrate?

A

a highly prevalent nitrogen source in the environment

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18
Q

where is fumarate highly prevalent?

A

in the cell as it is a citric acid cycle intermediate but has less energy compared to nitrate

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19
Q

what is respiratory nitrate reductase?

A

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

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20
Q

what does Fdn-Nar stand for?

A

stands for formatedehydrogenase oxidative complex

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21
Q

what is Fdn-Nar?

A

the prototypical redox loop

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22
Q

what is the electron carrier for Fdn-Nar?

A

menaquinone

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23
Q

what is the reductive complex for Fdn-Nar?

A

nitrate reductase

24
Q

when is formate produced?

A

produced during fermentation in E coli

25
Q

what increases energy gain in terms of formate?

A

detoxifying formate increases energy gain

26
Q

what is Frd?

A

fumarate reductase

27
Q

what is fumarate reductase?

A

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

28
Q

what is the last ditch option for oxidative phosphorylation?

A

fumarate reductase (Frd)

29
Q

what are the 3 alternative roles of the electron transport chain?

A

redox balance
radical detoxification
protect other enzymes

30
Q

what is redox balance?

A

maintains NADH/NAD+ to promote catabolic processes eg NDH2

31
Q

what is radical detoxification?

A

no electron transport chain where cytochrome bd can detoxify hydrogen peroxide

32
Q

what is the function of NQR?

A

translocates sodium

33
Q

what is the function of NADH dehydrogenase?

A

generates a membrane potential

34
Q

what is NDH2?

A

a type II NADH dehydrogenase involved in non-proton pumping

35
Q

how i does the alternate role of the ETC protect other enzymes?

A

by inactivating nitrogen fixing enzymes by oxygen to use oxidases

36
Q

what is proton motive force?

A

a chemical product of proton pumping reactions and subject to equilibrium chemistry

37
Q

what is the result of a high PMF?

A

a high PMF shifts equilibrium to substrates therefore is no longer spontaneous and this is called back-pressure showing no need for homeostatic balance

38
Q

what is the relationship between catabolic:anabolic balance and non-proton pumping ETC’s?

A

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

39
Q

what is the result of low biomass synthesis?

A

low ATP demand

40
Q

what is the result of increased ATP in terms of biomass synthesis?

A

more biomass and can cause accidental exit from persistence

41
Q

what are the alternate strategies to increase ATP?

A

ATP hydrolysis and transporters that use H+

42
Q

what determines differences in ETC configurations?

A

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

43
Q

what is TCA (the citric acid cycle) rerouting?

A

the production of NADH and FADH2

44
Q

why is TCA rerouting not always desirable?

A

because of back pressure or the lack of a terminal electron acceptor

45
Q

when are alternative pathways that avoid NADH production used?

A

used under hypoxia or for antibiotic persistence

e.g mycobacterium tuberculosis

46
Q

what direction does rTCA operate in?

A

rTCA (reverse TCA cycle) operates in the reverse direction as it is reductive rather than oxidative with many enzymes replaced, especially those performing decarboxylation

47
Q

why does CO2 not need photosynthesis?

A

because CO2 is fixed from the atmosphere without needing photosynthesis

48
Q

what branches do a TCA half cycle have?

A

a reductive branch and an oxidative branch

49
Q

what does the 2 branches of the TCA half cycle allow?

A

allows for the production of key precursors while fumarate is used as the terminal electron acceptor

50
Q

what does the genome of the TCA half cycle typically lack?

A

typically lacks alpha-KG dehydrogenase or it is not expressed anaerobically

51
Q

when are facultative/obligate anaerobes that are normally fermenters used?

A

used if there is no or limited citric acid cycle

52
Q

what is the ETC used for in terms of NADH?

A

the ETC is used to regenerate NADH to gain extra energy and avoid toxic end products

53
Q

what is the relationship between opportunistic pathogens and energy for infection?

A

opportunistic pathogens can use extra energy for infection

54
Q

what links central carbon metabolism with electron transport chains (ETC’s)?

A

redox balance

55
Q

what is the relationship between maintaining redox balance when ETCs fail and fermentation?

A

fermentation maintains redox balance when ETC’s fail but fermentation end products need to be secreted

MICR221 Lectures 1-38 (10 decks)

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