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Metabolic regulation > Microbial metabolism > Flashcards

Microbial metabolism Flashcards

1
Q

What does the nitrogen cycle maintain?

A

pool of biologically available nitrogen

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2
Q

What do Nitrosomonas do?

A

NH4+ → NO2-

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3
Q

What do Nitrobacter do?

A

NO2- → NO3-

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4
Q

Why does ammonia stay in soil more regularly than nitrate?

A

Nitrate is readily assimilated by plants, but is water soluble and is easily leached from the soil. However, positively charged ammonia is adsorbed to negatively charged clay soils

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5
Q

What kind of process is denitrification?

A

Anaerobic

reduction

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6
Q

What is ammadox?

A

Ammonia is oxidised to dinitrogen anaerobically using nitrite as an electron acceptor process is called anammox
performed by bacteria called
Planctomycetes

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7
Q

What special organelle does planctomycetes have that stops hydrazine diffucing across the membrane?

A

Ladderane

fused cyclobutane rings of ladderanes pack tightly together to form a dense barrier

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8
Q

Is the reducion of nitrogen to ammonia exergonic?

A

Yes

with high energy barrier

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9
Q

How is activation enegry of nitrogen fixation overcome in biological fixation?

A

Binding and hydrolysis of ATP

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10
Q

What is Nitrogen fixation catalysed by?

A

Dinitrogenase reductase and dinitrogenase

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11
Q

Describe the structure of Dinitrogenase Reductase?

A

MW= 60kDa
is a dimer (identical subunits)
4Fe-4S cluster at the interface and a binding site for ATP/ADP on each subunit

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12
Q

Describe the structure of Dinitrogenase?

A

Two types of cofactor

i) two p clusters consisting of bridged pairs of 4Fe-4S clusters
ii) Two iron molybdenum cofactors containing sulphur and homocitrate

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13
Q

How are electrons transfered from pyruvate to dinitrogenase?

A

Via ferredoxin( or flavodoxin) and dinitrogenase reductase

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14
Q

What does Dinitrogenase reductase do?

A

reduces dinitrogenase one electron at a time with at least 6 electrons required to fix one molecules of N2

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15
Q

Why are there 8 electrons per N2 molecule in nitrogen fixation?

A

6 electrons to fix one N2

2 electrons to reduce H+ to H2

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16
Q

explain e- flow in nitrgenase reductase?

A

Only reduced nitrogenase reductase with 4Fe-4S in oxidation stae +1 with two MgATP molecules can associate with nitrogenase.
During this MgATP are hydrolysed to MgADP
single electron tranfered from Fe protein (4Fe-4S) cluster into the MoFe protein.
Fe protein then regenerated

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17
Q

in Nitrogenase complex what is the site of substrate binding and reduction? evidence?

A

FeMo cofactor
Certain mutant strains that are deficient in FeMo cofactor biosynthesis are inactive, but can be activated by the addition of an isolated FeMo cofactor
In a CO-inhibited MoFe protein, electron-nuclear double resonance (ENDOR) spectroscopy shows that the CO binds to the FeMo cofactor, not to the P cluster

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18
Q

What does the p cluster do?

A

mediates electron transfer between the Fe protein and the substrate reduction site of the feMo cofactor because
X-ray crystal structures place the P cluster between the Fe protein [4Fe-4S] cluster and the FeMo cofactor

Amino acid substitutions between the P cluster and the FeMo cofactor perturb the intramolecular transfer of electrons from the P cluster to the FeMo cofactor

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19
Q

How do Leguminous plants remove o2

A

leghaemoglobin

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20
Q

Why is No toxic to bacteria

A

diffuse across bacterial membrane
cause respiratory inhibition and cell death
No can react with superoxide (made by NADPH oxidase) to form peroxynitrite this can nitrate protein tyrosine residues

21
Q

How do Bacteria encounter No during infection

A

dietary nitrite with stomach acids produce NO
Reduction of nitrate and nitrite by gut bacteria
Production via iNOS and eNOS

22
Q

How does the immune system respond to bacterial antigens?

A

Gram negative pathogens have LPS moieties
Two glucosamine residues are bound to six fatty acids, and a complex oligosaccharide
o specific chain determines serotype of the bacterium

In response to bacterial lipopolysaccharide (LPS), a signalling mechanism triggers the production of nitric oxide (NO) by iNOS in macrophages and neutrophils.

23
Q

Describe iNOS

A

N terminal
Oxygenase domain initial binding for substrate uses a haem prosthetic and BH4
C terminal domain Reductase (FMN and FAD)
Calmodulin binding group between iNOS isoform calcium sensitibe

24
Q

Mechanism for NOS?

A

Some isoforms of NOS are activated by Ca2+/calmodulin (e.g. endothelial eNOS)
NO stimulates guanylate cyclase which increases cGMP levels: this inhibits calcium entry into the cell resulting in diminished eNOS-dependent NO production
iNOS is calcium insensitive binds CAM permenantly

25
Q

How do Ecoli combat CO toxicity?

A

No is converted to nitrate or nitrous oxide by flavohaemoglobin Hmp under aerobic or anaerobic conditions respectively
NO is converted to nitrous oxide via the Flavorubredoxin/Flavorubredoxin Reductase system NorVW under anaerobic conditions.

NO is reduced by the periplasmic cytochrome c nitrite reductase NrfA.

The diiron protein YtfE repairs iron-sulphur clusters damaged by nitrosative stress.
An NO-tolerant respiratory oxidase is induced, Cytochrome bd-I (or CydAB), which facilitates aerobic respiration under microaerobic conditions.

26
Q

How does Cytochrome bd confer resistance to No mediated respiratory inhibition in E coli?

A

facilitates growth of bacteria in the presence of NO

27
Q

How does flavohaemoglobin Hmp of E coli detoxify NO?

A

NO is detoxified to nitrate or nitrous oxide under aerobic or anaerobic conditions, respectively:

28
Q

How is Hmp regulated?

A

Transcriptional regulator NsrR represses hmp transcription in the absence of NO upon NO exposure iron sulphur clused nitrosylated causing loss of DNA binding hmp expression is then induced.
regulated at transciptional lebel by homocysteine.

29
Q

Hmp regulation anaerboic conditions?

A

NO reacts with the iron sulphur cluster of FNR

alleviates repression of hmp gene

30
Q

How can NO cause antibiotic resistance?

A

bNOS

31
Q

What does Hydroxamate do?

A

import iron

32
Q

What are iron binding agents called?

A

siderophores

33
Q

What are Enterobactins?

A

produced by bacteria
Chelate extracellular iron.
siderophores
bind iron extremely tightly

34
Q

What kind of pathogens utilise haem as an Fe source?

A

Gram negative pthogens

35
Q

Explain regulation of iron uptake genes by Fur

A

Fur is a transcriptional repressor
under condiitions of low iron apo-fur dissociates from the promoter regions of iron-responsve genes allowing transcription to take place.

36
Q

What are Lf and CP produced by?

A

Neutrophils

37
Q

What does the host do in resoinse erythrocyte lysis?

A

hemopexin sequesters liberated haem.

haptoglobin sequester haemoglobin

38
Q

How does S aureus compete for iron with the host?

A

Expression of S aureus iron acquisition systems. Alleviation of FUr mediated transcriptional respression.
Produces sideophores to scavenge iron from serum.#
Isd catalyses extraction of haem through cell wall

39
Q

Explain Isd system?

A

isdC transports haemto the isdDEF membranetransport system.

40
Q

How do metals help s.aureus combat host defences?

A

iron deals with NO and peroxide
Manganese
superoxide

41
Q

When are secondary metabolites formed?

A

End of exponential growth or during stationary phase
its not needed for growth and repoduction
highly dependent on growth conditions.

42
Q

What are the most well known auto inducers?

A

gama butyrolactones of the actinomysetes (Gram+)
AHL of Gram-
Oligopeptides of Gram+ (bacteriocins)

43
Q

example of Gama butrolactones?

A

A factor

44
Q

What can A factor do?

A

induce Antibiotic production becuase stimulates the formation of more than 10 mRNA transcripts

45
Q

A factor mechanism?

A

A factor binds to ArpA repressor is emoved from DNA binding site allowing expression of target genes

46
Q

What is a modified Bacteriocins called?

A

lantibiotics

47
Q

How is bacteriocin production regulated?

A

Quorum sensing

48
Q

What has the smallest genome?

A

Endosymbionts and parasites

archaeon nanoarchaeum equitans 490kbp

Metabolic regulation (3 decks)

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