Central Metabolism: Funneling all nutrients into central pathways

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Central MetabolismFunneling all nutrients into
central pathways

• Many other molecules besides glucose can serve as
  a source of carbon.

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Central MetabolismA source of building blocks
for biosynthesis
BUT, these molecules cant be broken down to CO2
for energy AND used for biosynthesis
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Other ways to make ATP

• 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.

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Whats 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

• 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.

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Lessons from Fermentation

• Fermentation is inefficient. If C6H12O6 has lots
  of energy-rich Hs, 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.)

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Anaerobic respiration

• 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.

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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
• 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
Multiple choice score
Final curved, corrected, or adjusted score.
Correct answers. What you put if different.