Anaerobic and Aerobic metabolism L14 Flashcards
what is redox/reduction potential
ε is a measure of the tendency of a chemical speciesto acquire electronsand thereby bereduced
what is reduction potential measured in
volts (V), or millivolts (mV)
what are the reduction potentials foreach species like
each species has its own intrinsic reduction potential
the more positive the potential, the greater the species’ affinity for electrons and tendency to be reduced
what is the terminal electron acceptor in anaerobic respiration
a molecule other than oxygen
- strict anaerobes
- facultative anaerobes
what does the pathways and energy yields depend on
exact electron acceptor
do the more anoxic or oxic bacteria grow fastest
oxic grow fastest as get energy
do the more anoxic or oxic bacteria grow slowest
very anoxic bacteria don’t generate as much energy from electron transport system so grow very slowly
what is FNR
transcription regulator
where is FNR
cytoplasm
when is FNR inactivated
inactivated by reaction with oxygen
what happens if FNR is inactive
cant bind to DNA to affect gene expression
what happens in the absence of oxygen to FNR
active form of FNR represses the expression of both the cytochrome d (cydAB ) and cytochrome O (cyoABCDE) operons
Also induces the nar genes required for production of nitrate reductase
what happens in the regulation of gene expression by redox-sensitive Arc and FNR pathways
- High [O2] ArcB predominates – cyo O made from cyoABCDE
- [O2] drops, ArcB-P formed; ArcA-P down regulates cyoABCDE and induces cydAB
- [O2] absent FNR activated; cyoABCDE and cydAB repressed other electron acceptors induced
what happens to the TCA cycle during anaerobic respiration
becomes branched and generates less NADH
what happens to the TCA functions under anaerobic conditions
TCA functions mainly to supply intermediates to biosynthesis
what happens to the left branch reaction under anaerobic conditions in TCA
Left branch reactions reversed and Succinate produced from Oxaloacetate Succinate dehydrogenase (Sdh) replaced by Fumarate reductase
what is TCA cycle
biosynthetic pathway
why do these changes happen in TCA cycle when anaerobic
enzymes need certain environment to work in
cant work in no oxygen
what can happen to an organic compound in aerobic repsiration
electron flow form oxygen
this forms ATP from proton motor force
carbon flow leads to biosynthesis
can form carbon dioxide
what can happen to an organic compound in anaerobic respiration
electron flow: - nitrate ions - sulfate ions - organic electron acceptors this the forms ATP from proton motor force
carbon flow cause biosynthesis
form carbon dioxide
what is respiration
O2 or some other atom serves as terminal electron acceptor
=
what is fermentation
oxidation/reduction reactions occur in the absence of a terminal electron acceptor to generate energy
what is involved in substrate level phosphorylation
aerotolerant anaerobes
facultative anaerobes under anaerobic conditions and in stationary phase of growth
strict anaerobes
what are the pathways involved in fermentation
glycolysis
various reduction pathways
branched TCA cycle in operation
what is the net result of fermentation
some C atoms converted to CO2; ; the rest excreted
2 ATP molecular from one molecule of glucose
what happens in stage 1 of anaerobic respiration
preparation
what happens in stage 2 of anaerobic respiration
oxidation
what happens in stage 3 of anaerobic respiration
pyruvate goes through various different phosphorylation reactions, can get energy, but also lactate, ethanol, acetyl aldehyde, formate
Which of the pathways predominates depends on exactly what nutrients the bugs are given
what is the strickland reaction
coupled oxidation and reduction of amino acids to produce organic acids and to release energy
AAs acts as both electron donor and acceptor
Both AAs are converted to carboxylic acids
Donor = lose a carbon
Acceptor = stays same length
what uses the strickland reaction, what does it produce
Used by amino acid-fermenting microbes to produce ATP by substrate level phosphorylation
why is oxygen a ‘killer’
At the molecular level oxygen is a killer
Produces free radicals
Causes oxidative damages
what is the benefit of oxygen
However, oxygen is a hugely efficient terminal electron acceptor
Allows efficient use of organic carbon for faster growth
what is oxygen like
powerful oxidant and excellent electron acceptor
how is superoxide formed
O2+ e- –> O2-
how is hydrogen peroxide formed
O2- + e- + 2H+ –> H2O2
how is hydroxyl radical made
H2O2 + e- + H+ –> H2O + OH.
how is water formed
OH. + e- + H+ –> H2O
what is the overall oxygen protecting enzyme equation
O2 + 4e- + 4H+ –> 2H2O
how is oxygen linked to protection
Cells have evolved enzymes which break down toxic oxygen products
where is peroxidase
Present in some aerotolerant bacteria that lack catalase (e.g. lactic acid bacteria)
what does peroidase do
decomposes H2O2 using electrons from NADH2 to reduce peroxide to H2O
where is superoxide reductase
in strict anaerobes
what does superoxide reductase do
reduces superoxide without producing O2
what anaerobic jar technique is used for small scale growth studies
Brewer Jar or similar container are used
basic principle of all anaerobic jars is the same:
Remove oxygen from chamber: hydrogen and oxygen with catalyst form water
what happensin the disposable gas pak
H2-CO2 generator used to carry out the reduction of O2 and simultaneously replace it with a CO2 atmosphere
what does the disposable gas pak contain
sodium borohydride and sodium bicarbonate
small packet of palladium-coated alumina pellets to act as a catalyst in the reduction of O2 to H2O
what reaction occurs in the disposable gas pak
sodium borohydride and sodium bicarbonate react together when H2O added to produce H2 and CO2
how can anaerobic conditions be produced
using the evacuation-replacement procedure
the air within the jar is removed by vacuum pump and replaced
with a mixture of 85% N2, 10% H2, and 5% CO2 (pump in gas you want)
Tending to enhance CO2 – as what they require for growth
what happens in the branch chain TCA cycle when turns anaerobic
need to produce a new enzyme in order to produce succinate, lose a lot of energy as not a continuous cycle – growth is much slower as cant keep using the glucose
what is the electron transport chain like when oxygen is available
glycolysis producing reducing agents which are then used to pump out H+ ions (later used to generate ATP), cyt O responsible for pumping out one H+ ion. overall 4H+ions out
what is the electron transport chain like when oxygen is not available
using nitrate reductase, the proteins at the end of the system change, only 3H+ ions pumped out as nitrate reductase cannot pump out H+ ion, thus less ATP
what changes in the electron transport chain when no oxygen is available
E. coli starts to produce cyt O, when become completely anaerobic this is replaced by nitrate reductase as the electron acceptor
3H+ ions pumped out instead of 4H+
so less ATP
what happens in the overall fermentation scheme
Organic compound comes in, makes intermediates (act as electron carriers)
NADH brought back into other molecules then forms reduced organic compounds (fermentation product)
what happens if different microbes are added to fermentation
Put in different microbes, different versions of reduction reactions – produce different molecules at the bottom which causes different flavours e.g. cheese
what diagnostic tests are obligate aerobes and most facultative anaerobes positive and negative for
+ve superoxide dismutase
+ve catalase
-ve peroxide
what diagnostic tests are most aerotolerant anaerobes positive and negative for
+ve superoxide dismutase
-ve catalase
+ve peroxide
what diagnostic tests are obligate anaerobes positive and negative for
-ve superoxide dismutase
-ve catalase
-ve peroxide
Obligate anaerobe has non of these enzymes as they all produce oxygen
what is superoxide dismutase like
aerobes
facultative anaerobes
some aerotolerant anaerobes
NOT strict anaerobes (generates O2)
what is catalase like
most strict aerobes
facultative anaerobes
not usual in aerotolerant anaerobes
NOT strict anaerobes (generates O2)
