ESM 219

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ESM 219

• Lecture 4 Energetics

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Conceptwhat microbes need

• Carbon source
• Energy source
• N, P, S and trace minerals
• the right environmental conditions (pH, temp,
  salinity..)
• Terminal electron acceptor

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Concept energy uses and orgins

• How is the energy used?
• 1) transport
• 2) biosynthesis (anabolism)
• 3) polymerization
• 4) maintenance (regulation of pH, osmotic
  pressure,
• motility)
• All biochemical reactions metabolism anabolic
  are biosynthetic catabolic are energy generating
• Where does energy come from?
• Breaking chemical bonds (inorganic or organic
  substrates) chemotrophs
• Sunlight phototrophs

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Free energy Energy from chemical bonds is
internal energy that is released, the fraction
available to do work is free energy ?G ?H
- T ?S 2nd law of thermodynamics entropy
increases ?G change in free energy, or the
energy available to do work ?H change in
enthalpy (internal energy) ?S change in
entropy T temperature (constant isothermal
conditions)
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Free energy
?Go stnd. free energy of a reaction when all
reactants are at 1 mol/L, 1 atm pressure ?Go
reactants are at 1 mol/L, 1 atm and pH is 7 if
?G is negative, reaction is spontaneous and
energy yielding exergonic if ?G is positive,
reaction is non-spontaneous and energy requiring
endergonic
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Concept oxidation reduction reactions for
energy generation

• Electron donor (reduced) energy source
• Electron acceptor (oxidized) the necessary
  other half of gaining energy from a potential
• Half reactions one for each oxidation and
  reduction
• Full reaction the sum of the half reactions
• Redox tower depicts redox pairs with oxidized
  material on left, reduced on right coupled pairs
  with greatest fall yield the most energy

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Concept Energy Storage

• Energy is stored in ATP
• ATP is used to fuel reactions in cells
• AMP, ADP, ATP (Figure 2.1)
• ATP adenosine 5triphosphate carrier of energy
  in life
• 3 adenosine 5nucleotides (AMP, ADP, ATP)
• ?Go -36 kJmol-1

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• energy of hydrolysis must be coupled to other
  reactions or its lost

e.g. formation of glutamine (amino acid) from
glutamate ammonia overall glutamate NH4
ATP ? glutamine ADP Pi H 2 reactions
energy requiring and energy yielding glutamate
NH4 ?glutamine H2O H ?Go 15.7
KJ/mol ATP H2O ? ADP Pi ?Go -36.0
KJ/mol ?Go -20.3 KJ/mol
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How is ATP Generated?(2 ways)

• I. Substrate level phosphorylation ATP
  formation coupled
• to enzymatic transformation of substrate
  containing
• a high-energy phosphoryl bond to its product.
• (e.g., in glycolysis, conversion of
• phophoenolpyruvate to pyruvate). Accounts for
  ATP
• generation during fermentation (partial
  oxidation and thus
• partial energy potential energy release).
  Cytoplasmic process.

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How is ATP Generated?(2 ways)

• II. Electron-transport phosphorylation
  Membrane-associated
• mechanism where ATP formation is coupled with
• flow of electrons from donor to acceptor.
  Occurs
• in respiratory chain and in photosynthetic
  reaction
• sequences.

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Where is ATP made during ETP? Mitochondria
inner membrane chloroplasts thylakoid
membrane bacteria cyanobacteria cytoplasmic
membrane 2 protein assemblies in these
membranes 1. All contain ATPase a.k.a ATP
synthetase (makes ATP from ADP and
Pi) 2. Mitochondria and bacteria have
respiratory chain that transfer reducing
equivalents from substrate to electron
acceptor Chloroplasts and photosynthetic
bacteria have a system with light-harvesting
pigments (chlorophyll or bacteriochlorophyll)
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Chemiosmotic hypothesis (Mitchell,
1966) explains how energy source and ATP
synthesis are coupled ATP hydrolysis or electron
transfer generates electrical (membrane)
potential, ?? chemical potential, ?pH Protons
are extruded outside the membrane and a proton
motive force results. Uncouplers are chemicals
that short circuit the electrochemical gradient
(hydrophobic, weak acids) by moving back
and forth across membranes ,becoming protonated
and deprotonated in the process (2,4 dintrophenol)
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Intermediate carriers Energy doesnt flow as
free electrons (e-). Instead, intermediate
carriers are used. IMPORTANT most
oxidation-reduction reactions wouldnt happen at
any reasonable rate if carriers were not present
to transfer electrons from from a primary
electron donor to terminal electron acceptor.
Carriers are either freely diffusible (NAD or
NADP) or are attached to the cell membrane.
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Terminology (trophs) in microbial metabolism

• Energy source
• Chemo- chem bonds
• Organo organic
• Litho-inorganic
• Photo- sunlight
• e- acceptor
• Aerobic oxygen
• Anaerobic- not O2

• Carbon
• Hetero organic
• Auto inorganic

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