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Microbiology 200 > Topic 3-L4 - Catabolism in chemoorganotrophs > Flashcards

Topic 3-L4 - Catabolism in chemoorganotrophs Flashcards

1
Q

There are three different terms used for how ATP is generated:

A

1) Substrate level phosphorylation.
2) Oxidative phosphorylation
3) Photophosphorylation

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2
Q

Substrate level phosphorylation:

A

ATP generated as a product of a metabolic reaction – energy from an exergonic reaction (energy-rich bone) used to power transfer of phosphate onto ADP to form ATP

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3
Q

Oxidative phosphorylation:

A

Energy from Electron transfer reactions generate a proton motive force, that is used to generate ATP using ATP synthase

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4
Q

Photophosphorylation:

A

Energy captured from light is used to generate a proton motive, that is used to generate ATP using ATP synthase

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5
Q

For many chemoorganotrophs, sugars like glucose are a preferred energy source ?

Can other organic compounds can also be used to generate energy ?

A

Yes

Yes

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6
Q

Many other sugars (disaccharides, polymers, monomers other than glucose) can be converted to

A

glucose or into an intermediate in glycolysis or the citric acid cycle

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7
Q

Glucose to CO2 – Slow and controlled oxidation, not a single step which would release a tremendous amount of energy all at once.

A
  • not in a single step
  • releases ALOT of E
  • happens over a series of rxns in which high E substrates are oxidized to lower E molecules, ultimately into CO2
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8
Q

Is glycolysis conserved in all domains of life?

A

YES

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9
Q

Glycolysis

A
  • doesn’t require O2

- Can be followed by either respiration or fermentation

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10
Q

2 stages for glycolysis

A
  • investment stage and second stage
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11
Q

Investment stage

A
  • requires ATP
  • no redox rxns
  • starts and ends with 6 carbon mol.
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12
Q

Stage 2 of glycolysis

A
  • ATP generated via substrate-level phosphorylation
  • ATP generated when intermediate I (phosphoenolpyruvate - PEP) – high energy
    phosphate bond
  • pyruvate final product
    (important metabolite)
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13
Q

Between investment stage and stage 2 of glycolysis

A

NAD+ reduced to NADH (redox rxn)

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14
Q

Substrate level phosphorylation in glycolysis produces

A

2 ATP per glucose

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15
Q

NADH (in glycolysis ) is useful for

producing additional

A

ATP

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16
Q

Glycolysis Lacks redox balance! Produces NADH, but no electron acceptor to regenerate NAD+. Redox balance can be restored using

A

fermentation or via the citric acid cycle/respiration.

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17
Q

Glycolysis generated

A

2 pyruvate and 2 NADH per glucose

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18
Q

Oxidation of pyruvate can be used to

A

generate a great deal more ATP using the citric acid cycle/respiration (preferred pathway for chemoorganotrophs

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19
Q

For organisms who can’t for respiration to oxidize pyruvate, they must use

A

Fermentation

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20
Q

Before the CAC, pyruvate is converted to

A

acetyl-COA – acetyl-COA then enters the citric acid cycle

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21
Q

What else can be fed into the CAC?

A

other organic molecules (lipids, amino acids, etc)

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22
Q

What else can the CAC provide?

A

provides key metabolic intermediates used anabolic reactions

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23
Q

The CAC is a Sentra hub for metabolism - not just found in

A

aerobic chemotrophs

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24
Q

Where does CAC take place?

A

Mitochondria for eukaryotes

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25
Q

Steps for CAC

A

1) 2C acetyl-CoA + 4C oxaloacetate = 6C citrate
2) via series of oxidations, citrate converted to 4C oxaloacetate which begins another cycle with addition of acetyl-CoA mol.
3) 2 redox rxns occur, no CO2 released from succinate to oxoacetate
4) oxaloacetate can be made from 3C compounds by addition of CO2

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26
Q

Substrate level phosphorylation in CAC produces

A

1 more ATP per pyruvate (2 per glucose)

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27
Q

CAC Produces how many NADH and FADH?

A

2 NADH and 1 FADH2 per pyruvate (2x per glucose)

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28
Q

This reducing power (NADH/FADH2) is fed into __________. Why?

A

electron transport chain

to generate more ATP or anabolic reactions (NADPH).

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29
Q

The electron transport chain is also known as

A

Respiration

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30
Q

Where does ETC take place

A

Takes place in the cytoplasmic membrane (inner mitochondrial membrane for eukaryotes)

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31
Q

In ETC, redox balance is

A

restored and oxidized forms of electron carriers (NAD+) regenerated

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32
Q

How does the ETC work?

A

1) Electrons passed down a series of electron carriers with increasingly +ve reduction potentials (Eo’) until a final electron
acceptor (‘external’ or ‘terminal’ electron acceptor) is reduced

2) Protons pumped out of the cell in the process – generates the proton motive force (ultimately used to generate ATP)

33
Q

For aerobic respiration (most efficient) ___ is the terminal electron acceptor in ETC.

A

O2

34
Q

For anaerobic respiration, what kind of terminal electron acceptor used?

A

A wide range of terminal acceptors can also be used (anaerobic respiration)

35
Q

Electron carriers generated by

A

glycolysis/CAC

36
Q

In ETC, NADPH is generally used primarily for

A

biosynthetic reactions (rather than ATP generation)

37
Q

In ETC, key electron carriers are

A

1) NADH Dehydrogenase & Flavoproteins
2) Iron-sulfur proteins
3) Quinones (such as ubiquinone)
4) Cytochromes

38
Q

NADH Dehydrogenase & Flavoproteins

A
  • Where NADH electrons are deposited (to recycle back to NAD+)
  • NADH Dehydrogenase transfers 2
    electrons to a flavoprotein
  • Flavoproteins contain either FAD/
    FADH 2 or FMN/FMNH2.
39
Q

Iron-sulfur proteins

A
  • Iron sulfur clusters are metal cofactors used by many different proteins involved in electron transfers
  • ETC complexes often contains multiple Fe/S clusters
  • Oxidation state and reduction potential
    (Eo’) varies depending on nature of cluster & protein
40
Q

Quinones (such as ubiquinone)

A
  • they aren’t proteins – small
    molecules that move within membrane
  • Accept 2 electrons, transfer to next
    carrier in chain
  • Often serve to link Fe/S proteins to
    cytochromes
41
Q

Cytochromes

A
  • Cytochromes are proteins that contain heme prosthetic groups (iron
    coordinated within organic molecule)
  • Different proteins/different heme
    groups, different reduction potentials
  • ETC Complexes often contain multiple
    cytochromes – typically the last stop
    before terminal acceptor
42
Q

In the ETC, Electrons transferred from

A

lower reduction potential carriers (such as flavoproteins, Fe/S proteins) to higher reduction potential carriers (such as cytochromes) and then ultimately to their final electron acceptor (O2 for aerobic respiration).

43
Q

In the final step of ETC, does the final electron acceptor get used up?

A

YES, needs of continuous source to keep going.

44
Q

In the ETC, what are complexes (complex l, ll, lll)

A

multiple proteins (and often multiple electron acceptors). Can include proton pumps that couple energetically favourable electron transfer to proton pumping

45
Q

Which complexes do e- enter at ?

A

Complex l and ll

46
Q

ETC e- pathway through the complex l

A

Complex I starts with NADH (lower Eo’) – pumps 4 more protons per 2e…generates more energy

47
Q

ETC e- pathway through the complex ll

A

Complex 2 starts with FADH2 (higher Eo’), pumps fewer protons

48
Q

Once e- passed through either complex ll or l,

A

quinone is reduced – passes electrons

on to complex III

49
Q

What’s the terminal e- acceptor

A

O2 (aerobic respiration) , generates H2O

  • From NADH to H2O = 10 protons pumped (per NADH)
50
Q

Individual microbes can operate multiple different electron transport chains with different components – sometimes simultaneously ?

A

Yes

51
Q

Common electron examples that aren’t O2 are

A

NO2^- and SO4^(2-)

52
Q

Do microbes have to always use a single terminal electron acceptor

A

NO, Some microbes have the ability to use multiple different terminal
electron acceptors, depending on availability

53
Q

Can different electron donors be fed into ETC?

A

Yes

54
Q

What is ATP synthase and where’s it found

A

Enzyme located in cytoplasmic membrane (prokaryotes) and in mitochondrial membrane (eukaryotes)

55
Q

How does ATP synthase produce ATP?

A

Protons flow back along their

gradient –generates mechanical energy – used to power ADP à ATP (ATP synthesis)

56
Q

ATP synthase - mechanism

A

Fo and F1 parts connected by stalk (y) – Fo in membrane – F 1 in cytosol

  • Fo : P+ flow through, spins like turbine
  • F1 : held in place, drives conformational change
57
Q

How many H+ pumped and how many ATP made?

A

3.3 H+ pumped to generate 1 ATP

58
Q

Is ATP formation in ATP synthase reversible?

A

YES. ATP hydrolysis can generate PMF

E.g. – fermentative organisms

59
Q

Oxidative phosphorylation makes a lot of ATP?

A

YES

60
Q

aerobic respiration of glucose

A
  • Cell takes in: High energy electron donor (glucose) and excellent e- acceptor (O 2)
  • Traps energy of moving those electrons to a lower energy state in the form of ATP
  • Spits out fully oxidized CO2 and generates H2O as biproduct
61
Q

Many chemoorganotrophs are metabolically flexible

A

Chemoorganotrophs have preferred energy sources (e.g. glucose) that they will use first, if available

  • In a pinch (probably quite common) they can use of a wide range of high energy organic molecules
62
Q

Many bacteria used a pathway called __________ to convert fatty acids to acetyl-CoA, which can then be fed into CAC/respiration

A

β-oxidation

63
Q

Can chemoorganotrophs be consumed for E source

A

Amino acids can be converted to entry points to the citric acid cycle
(e.g., pyruvate).

64
Q

Catabolite repression

A

if a better energy source (e.g. glucose) is around, enzymes to use other energy source inhibited/not expressed

65
Q

The glyoxylate cycle

A
  • Variation on the citric acid cycle
  • Used in order to grow on 2-carbon
    molecules like acetate/acetyl CoA
  • Because oxaloacetate (4 carbon)
    gets drawn off for biosynthesis –
    need to regenerate extra to run
    citric acid cycle
  • Produces less reducing power (less ATP) but provides oxaloacetatebuilding block for synthesis of amino acids, glucose, etc.
66
Q

E. coli is a facultative anaerobe meaning is can

A

live/grow with or without O2

67
Q

E.coli can

A
  • do aerobic respiration, anaerobic respiration & fermentation
  • Can assemble different electron transport chains. Under anaerobic conditions, can respire using nitrate (if available). If not available – fermentation as a last resort
68
Q

Nitrate respiration is less

A

efficient – pumps fewer protons than with O2

69
Q

Fermentation

A
  • Chemotrophic metabolism without the use of an external electron acceptor
  • Anaerobic!
  • Substrate-level phosphorylation can be used to generate ATP
  • Redox balance achieved by excretion of reduced fermentation products
70
Q

Lactic acid fermentation

A
  • Fermentation regenerates NAD+ and so maintains redox balance
  • Can continue to break down glucose for ATP…but generates little energy/ATP
  • Some bacteria are heterofermentive lactic acid fermenters – they generate mix of lactose + other fermentation products. Can be useful to avoid lactate accumulation
71
Q

Fermentation pathway used by

A

Yeast and to produce beer

72
Q

Ethanol fermentation produces

A

3C pyruvate produces CO2 (1C) and

ethanol (2C) – both excreted

73
Q

Ethanol fermentation

A
  • NAD+ replenished

- Saccharomyces cerevisiae – yeast widely used in food/beverage fermentations

74
Q

Ethanol fermentation…Beer!

A
  • The ethanol generated by yeast alcoholic fermentation used to make
    alcoholic beverages
  • The CO2 generated by alcoholic fermentation used to make dough rise
    (alcohol mostly evaporated off when baking the bread)
  • The CO2 can also be used to naturally carbonate – beer (also sodas like root beer…before modern “forced carbonation technology)
75
Q

In addition to glucose (via pyruvate), microbes can ferment a wide range of

A

organic compounds (E.g. fatty acids, amino acids, purine/pyrimidines, etc)

76
Q

Common theme:

A

Generate an energy-rich molecule (bond) that can be hydrolyzed to produce ATP, donate electrons to (reduce) a metabolite and excrete to obtain redox balance

77
Q

Fermentation can vary from a

A

last resort option to the sole source

of energy - depends on the microbe

78
Q

Laxative acid fermentation makes

A

2 lactate and 2 ATP

79
Q

Aerobic fermentation produces

A

6 CO2, 6 H2O, 38 ATP

Microbiology 200 (32 decks)

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