Transcript Transport of molecules into a bacterial cell

Central Metabolism:
Funneling all nutrients into central pathways
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•Many other
molecules
besides glucose
can serve as a
source of carbon.
Central Metabolism:
A source of building blocks for biosynthesis
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BUT, these
molecules can’t be
broken down to CO2
for energy AND
used for biosynthesis
Other ways to make ATP
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• Photosynthesis: light driven ATP synthesis.
• Anaerobic respiration: organic compounds oxidized,
electrons passed down e- transport chain to some
molecule other than oxygen (e.g. NO3, SO4).
• Inorganic molecules can be oxidized with ATP
synthesis by e- transport and chemiosmosis.
• Fermentation: common anaerobic pathway used by
many medically important bacteria.
What’s Fermentation for?
Glucose can be oxidized to pyruvic acid with the synthesis of
2ATPs. This alone is enough energy to live on. It depends on
the oxidation of NADH to NAD so that NAD is available to
accept electrons during the oxidation of glucose.
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Why fermentation-2
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Fermentation: “life without air”
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• Without O2 as an e- acceptor, NADH cannot be re-oxidized
to NAD.
• Even though aerobic metabolism can produce ~36 ATP from
1 glucose, the 2 ATP from glycolysis is enough.
• But glycolysis requires that NAD be reduced to NADH;
what happens when ALL the NAD becomes NADH with no
O2 to accept the H?
• Pyruvic acid is reduced, and the product thrown away; NAD
restored, glycolysis can be repeated, more ATP made.
• A variety of ways of solving this problem exist; many types
of molecules can be produced from fermentation.
Lessons from Fermentation
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• Fermentation is inefficient. If C6H12O6 has lots of
energy-rich H’s, so does C3H5O3 (lactic acid); the
product cannot be further metabolized and is thrown
away! Only a couple of ATPs are made.
• Fermentation is quick. Even though few ATPs are
made, they are made quickly.
• Fermentation is wasteful. Large amounts of
substrate (e.g. sugar) is used, making large amounts
of product (e.g. lactic acid, ethanol, etc.)
Anaerobic respiration
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• Not the same as fermentation
– Respiration involves the electron transport chain and ATP
synthesis by chemiosmosis.
– Most general biologists are very confused.
• Anaerobic means without oxygen
• Anaerobic respiration: organic (or inorganic)
molecule is oxidized, the removed electrons are sent
down the electron transport chain, and something
OTHER than oxygen is the electron acceptor.
– Carried out by anaerobic bacteria, but some aerobes can
reduce forms of N this way.
Anaerobic respiration
In this example, nitrate is reduced to nitrite. Other examples:
sulfate reduced to elemental sulfur (S) or S to sulfide (H2S).
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Bacteria and the fragility of existence
• Bacteria use ATP or the proton motive force to:
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Move
Synthesis proteins (lots of them)
Transport molecules into the cell
Synthesize cell materials
Homeostasis
• Bacteria do not store ATP
– Calculations: E. coli has enough ATP to last a few
seconds
– Thus, cells must keep on making it.
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Essay score
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score
Correct answers.
What you put if different.
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adjusted score.