BIO2041: Lecture 3

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  • Created by: LMoney
  • Created on: 14-05-14 10:39
what is redox potential?
(Eh - measured in volts) is a measure of the ability of a system to gain or lose electrons (ie to be reduced or oxidised)
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what does the redox potential determine?
whether or not oxidation-reduction reactions will take place- important as a source of energy
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An individual oxidation-reduction reaction is made up of two parts which are called?
redox couples- one oxidizing agent, one reducing agent
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what does the potential of a compound to be oxidised or reduced depend on?
Eo’
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if the standard redox potential is positive what does this mean?
The more +ve the value the greater the potential to be reduced – act as oxidising agent
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Whether or not a specific oxidation-reduction reaction will occur depends on the actual redox potentials- what do actual redox potentials depend on?
the concentrations of the reductant and oxidant within the redox couples
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what are some factors that affect the Eh (actual redox potential) of a system?
1) Concentrations of oxidant and reductant 2) Redox couples involved in reactions 3) pH ([H+]) 4) Oxygen concentration
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what is the Eh for the redox couple ½O2 + 2H+ + 2e => H2O?
+820 mV- very high
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The Eh range over which different microorganisms will grow is associated with their dependence on/tolerance to what?
oxygen
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what is the Eh range for Aerobes?
+500 to +300 mV
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what is the Eh range for Facultative anaerobe?
+300 to -100 mV
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what is the Eh range for anaerobe?
+100 to –250 mV
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what does it mean to the environment if the Eh is more +ve?
means environment is more oxidised
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what are these groupings (aerobes, anaerobes etc.) dependent on?
These groupings depend on what mechanisms the organisms use for their energy (ATP) generation
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what mechanism do obligate aerobes use?
Metabolise carbohydrate by glycolysis and TCA cycle with ATP generated by oxidative phosphorylation using oxygen as terminal electron acceptor
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what mechanism do microaerophiles use?
Same as obligate aerobes but can only survive at low oxygen concentrations – not more than 10%
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what mechanism do facultative anaerobes use?
If oxygen is present behave as aerobes but when oxygen is absent they use other compounds, either inorganic or organic, as terminal electron acceptor
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what mechanism do obligate anaerobes use?
Cannot grow in presence of oxygen. Generate energy by fermentation – organic terminal electron acceptors
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what mechanism do oxygen independent use?
Generate energy by oxygen independent mechanism, usually fermentation, even if oxygen is present
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which group is oxygen toxic to?
obligate anaerobes
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which superoxide anion can normal cell metabolism in the presence of oxygen result in?
O2-
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which antioxidant enzymes prevent the build up of potentially damaging superoxide?
superoxide dismutase (SOD) and catalase- Anaerobes do not produce these enzymes
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what do Lactic acid bacteria contain rather than catalase to help destroy the superoxide anion?
peroxidase
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what else do lactic acid bacteria use to help destroy the anion?
Mn
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what effects does Carbon Dioxide have on growth of microorganisms?
Carbon dioxide can be lethal or just inhibit growth- may displace oxygen required by aerobes. Also influences carboxylation/decarboxylation reactions.
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what happens when Carbon Dioxide dissolves in water?
forms the weak acid carbonic acid – effect on intracellular and extracellular pH
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what other factors can have an effect on microbial growth?
Antimicrobial factors
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which compounds found naturally in food may have antimicrobial properties?
1) Eugenol in cloves 2) allicin in garlic 3) lectins 4) lysozyme in eggs- May respond to presence of microbes by producing the antimicrobial
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can microbes synthesise minerals from precursors?
no, these must be provided/available
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how do various organic compounds that microbes need enter the cell?
Some may enter by diffusion across the membrane, others require transport proteins
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what happens to larger molecules that can't enter the cell directly?
Only molecules of a certain size can enter cell so some may have to be degraded extracellularly into their components and resynthesised after components enter cell
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what will growth rate be determined by?
by the amount of the most limiting nutrient
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which equation describes this relationship?
Monod equation
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cous
cous
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what does the redox potential determine?

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whether or not oxidation-reduction reactions will take place- important as a source of energy

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An individual oxidation-reduction reaction is made up of two parts which are called?

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Card 4

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what does the potential of a compound to be oxidised or reduced depend on?

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if the standard redox potential is positive what does this mean?

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