Definitions

1
Definitions

• Substrate level phosphorylation
• Chemical reaction coupled to ATP synthesis
• Example Pyruvate synthesis in glycolysis
• Oxidative (respiratory) phosphorylation
• Pumping of protons powered by electron transport
  with oxygen as terminal electron acceptor yields
  ATP
• Photophosphorylation
• Pumping of protons powered by absorption of
  light.
• Respiration
• a redox process in which electrons are passed
  along an electron transport chain.

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Central MetabolismFunneling all nutrients into
central pathways

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

3
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.
• Oxygenic (photosystem I and II)
• Uses chlorophyll, produces oxygen from water
• Anoxygenic (photosystem I only)
• Hs to reduce CO2 from other sources

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Other ways to make ATP-2

• Inorganic molecules can be oxidized producing ATP
  synthesis by e- transport and chemiosmosis.
• Examples Fe2 to Fe3, NH3 to NO2-
• Requires O2 as terminal electron acceptor

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icationET.jpg
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Anaerobic metabolism to make ATP

• Anaerobic respiration organic compounds
  oxidized, electrons passed down e- transport
  chain to some molecule other than oxygen (e.g.
  NO3-, SO4-2).
• Just like aerobic respiration but w/o O2
• Fermentation common anaerobic pathway used by
  many medically important bacteria.
• Electron transport not important in ATP
  production
• Organic molecules serve as electron acceptor
  (sink).

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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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Examples for fermentations

• Lactic acid fermentation
• Lactic acid
• Alcoholic fermentation
• Ethanol, carbon dioxide
• Mixed acid fermentation
• Lactic acid, formic acid, succinic acid, ethanol,
  H2, CO2
• Propionic acid fermentation
• propionic acid, acetic acid, and carbon dioxide

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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.)

12
Anaerobic respiration

• Not the same as fermentation
• Respiration involves the electron transport chain
  and ATP synthesis by chemiosmosis.
• Most general biologists misapply the term.
• 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 (growing anaerobically) can reduce forms
  of N this way.

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Anaerobic respiration-2
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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Anaerobic respiration-3

• Molecules of electron transport chain different
• Some aerobes and facultative anaerobes carry
  out anaerobic respiration
• A different set of electron carriers produced in
  response to lack of oxygen, or
• Oxygen is preferred electron acceptor others
  work if oxygen is not available.
• Example denitrification
• NO3- ? NO2- ? NO ? N2O ? N2
• Important environmentally fixed nitrogen lost
  under anaerobic conditions.

15
Anaerobic bacteria use incomplete citric acid
cycle for production of biosynthetic precursors.
They do not contain a-ketoglutarate dehydrogenase.
cronus.uwindsor.ca/.../7a371e9af805f74e85256a4f005
38021/FILE/Citric20acid20cycle.ppt
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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.
• Bacteria carefully regulate their use of energy!