MICR221 Lecture 9 - Respiration Without Oxygen

Question 1

what do facultative anaerobes use for respiration?

Answer 1

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

Question 2

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

Answer 2

fermentation

Question 3

what do bacteria use when oxygen is limiting for respiration?

Answer 3

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

Question 4

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

Answer 4

complex III-IV
cytochrome bo3
cytochrome bd

Question 5

what is complex III-IV?

Answer 5

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

Question 6

what is complex cytochrome bo3?

Answer 6

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

Question 7

what is the function of cytochrome bd?

Answer 7

works at low oxygen but pumps 3 fold less H+

Question 8

what do pathogens and facultative anaerobes use during microaerobiosis?

Answer 8

cyt-bd

Question 9

what are low affinity oxidases?

Answer 9

very inflexible with O2 not too high or too low

Question 10

what are an example of low affinity oxidases?

Answer 10

mycobacterium leprae that cause leprosy

Question 11

what is infection best on in low affinity oxidases?

Answer 11

best on extremities that is ideal for O2

Question 12

what do both low affinity and high affinity oxidases present?

Answer 12

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

Question 13

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

Answer 13

most cultured bacteria eg E.coli

Question 14

what are high affinity oxidases?

Answer 14

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

Question 15

what are anaerobic electron acceptors?

Answer 15

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

Question 16

what are 2 anaerobic electron acceptors?

Answer 16

nitrate and fumarate

Question 17

what is nitrate?

Answer 17

a highly prevalent nitrogen source in the environment

Question 18

where is fumarate highly prevalent?

Answer 18

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

Question 19

what is respiratory nitrate reductase?

Answer 19

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

Question 20

what does Fdn-Nar stand for?

Answer 20

stands for formatedehydrogenase oxidative complex

Question 21

what is Fdn-Nar?

Answer 21

the prototypical redox loop

Question 22

what is the electron carrier for Fdn-Nar?

Answer 22

menaquinone

Question 23

what is the reductive complex for Fdn-Nar?

Answer 23

nitrate reductase

Question 24

when is formate produced?

Answer 24

produced during fermentation in E coli

Question 25

what increases energy gain in terms of formate?

Answer 25

detoxifying formate increases energy gain

Question 26

what is Frd?

Answer 26

fumarate reductase

Question 27

what is fumarate reductase?

Answer 27

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

Question 28

what is the last ditch option for oxidative phosphorylation?

Answer 28

fumarate reductase (Frd)

Question 29

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

Answer 29

redox balance radical detoxification protect other enzymes

Question 30

what is redox balance?

Answer 30

maintains NADH/NAD+ to promote catabolic processes eg NDH2

Question 31

what is radical detoxification?

Answer 31

no electron transport chain where cytochrome bd can detoxify hydrogen peroxide

Question 32

what is the function of NQR?

Answer 32

translocates sodium

Question 33

what is the function of NADH dehydrogenase?

Answer 33

generates a membrane potential

Question 34

what is NDH2?

Answer 34

a type II NADH dehydrogenase involved in non-proton pumping

Question 35

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

Answer 35

by inactivating nitrogen fixing enzymes by oxygen to use oxidases

Question 36

what is proton motive force?

Answer 36

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

Question 37

what is the result of a high PMF?

Answer 37

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

Question 38

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

Answer 38

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

Question 39

what is the result of low biomass synthesis?

Answer 39

low ATP demand

Question 40

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

Answer 40

more biomass and can cause accidental exit from persistence

Question 41

what are the alternate strategies to increase ATP?

Answer 41

ATP hydrolysis and transporters that use H+

Question 42

what determines differences in ETC configurations?

Answer 42

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

Question 43

what is TCA (the citric acid cycle) rerouting?

Answer 43

the production of NADH and FADH2

Question 44

why is TCA rerouting not always desirable?

Answer 44

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

Question 45

when are alternative pathways that avoid NADH production used?

Answer 45

used under hypoxia or for antibiotic persistence | e.g mycobacterium tuberculosis

Question 46

what direction does rTCA operate in?

Answer 46

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

Question 47

why does CO2 not need photosynthesis?

Answer 47

because CO2 is fixed from the atmosphere without needing photosynthesis

Question 48

what branches do a TCA half cycle have?

Answer 48

a reductive branch and an oxidative branch

Question 49

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

Answer 49

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

Question 50

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

Answer 50

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

Question 51

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

Answer 51

used if there is no or limited citric acid cycle

Question 52

what is the ETC used for in terms of NADH?

Answer 52

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

Question 53

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

Answer 53

opportunistic pathogens can use extra energy for infection

Question 54

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

Answer 54

redox balance

Question 55

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

Answer 55

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