from last time

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from last time Pressure force/area Two
major pressures in plants. 1. The positive
pressure (turgor) inside living cells and thats
required for cell and tissue growth. 2. The
negative pressure (tension) that exists in the
cells of the xylem of transpiring plants.
In general well use units of pressure to express
the energy status of water, the water potential
. How is pressure like energy/volume?
2
So, we can use units of pressure to express the
energy status of water. Well see that water
tends to move from areas of higher to lower
energy/vol, or pressure.
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a bit more review.
The gas constant, R Remember PV nRT? R, the
gas constant makes the relationship among P, V,
n, and T work. R shows up in lots of energy
equations. Values and units for R 8.314 J mol-1
K-1 8.314 m3 Pa mol-1 K-1 Well use R a lot!
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• How to put some numbers to all the energy
• expended in doing the work of life.
• Chemical reactions - synthesizing compounds,
• degrading others
• Solute transport - maintaining concentration
• differences across membranes
• Maintaining electrical potentials and moving
• ions across charged membranes.
• How can we understand when these processes
  require energy and how much?

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Bioenergetics and Free Energy Free Energy, G, is
the energy available to do work. DG is the change
or difference (D) in G during a process or
reaction. DG equations help us understand
whether a reaction 1) yields energy and can
happen spontaneously (DG lt 0), 2) requires
energy input to occur (DG gt 0), 3) or is at
equilibrium (DG 0). We will use DG equations
for understanding bioenergetics of chemical
reactions and the transport of charged and
uncharged solutes.
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the free energy equations give us values of
energy per mole, J mol-1
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• ?G of a chemical reaction
• General equations
• ?G ?G0 2.3 RT log (K)
• or
• ?G ?G0 RT ln (K)

?G0 is the standard free energy change, defined
for standardized conditions. It allows
comparisons of ?G of different reactions.
K is the equilibrium constant K
(productproduct) (reactantreacta
nt) So, ?G ?G0 2.3 RT log (K) can be
written as ?G ?G0 2.3 RT log
(productproduct)
(reactantreactant)
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Example using a very important reaction ?G for
ATP hydrolysis ATP ? ADP Pi ?G0 - 33kJ
mol-1 In typical cellular conditions ?G 50
kJ mol-1 to 65 kJ mol-1, The reaction releases
energy and can happen spontaneously. Compare
with ATP synthesis ADP PI ? ATP ?G gt 0,
requires energy, is not spontaneous.
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2. Solute transport Transport is from C1 to
C2
C1
C2
-------------gt
The standard equation ?G 2.3 RT log C2/C1
There are 3 possibilities 1. C1 lt C2,
so log C2/C1 gt 0, so ?G gt 0 2. C1 gt C2,
so log C2/C1 lt 0, so ?G lt 0 3. C1
C2 so log C2/C1 0, so ?G 0 Which
happens spontaneously?
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2. Solute transport ?G 2.3 RT log C2/C1
transport is from C1 to C2 C1 gt C2
means that log C2/C1 lt 0 so ?G lt 0 This
can happen spontaneously, without energy input

C1
C2
-------------gt
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2. Solute transport ?G 2.3 RT log
C2/C1 transport is from C1 to C2 C2
C1 means logC2/C1 0 So, ?G 0,
equilibrium
C1
C2
lt----------gt
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Numerical example C2 100mM, C1 10mM
37 0C How much energy to transport a mole of C?
C1
C2
-------------gt
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?G 2.3 RT logC2/C1
Dimensional analysis - do the units make sense?
???G R T logC2/C1 Units
J mol-1 J mol-1 K-1 K
mol l-1/mol l-1
J mol-1 J mol-1
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Now fill in the numbers
?G 2.3 RT logC2/C1 ?G (2.3)(8.314 J
mol-1 K-1)(310 0K) log(100/10) 2.3 x
8.314 x 310 x 1 J mol-1 5928 J mol-1
or 5.928 kJ mol-1 Energy is required to move a
solute up a concentration gradient
C1
C2
-------------gt
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3. DG for ion transport ions are charged solutes


Fig. 6.4
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Biological membranes are electrically polarized,
like a battery.
K NO3- Ca2 SO4-2
Which ion requires the most energy to move
across the membrane, assuming the same
concentration gradient for all four?
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3. ?G for ion transport ?G zF ?Em z is
charge on the ion K 1, NO3- -1, Ca2
2, SO4-2 -2 other molecules have not net
charge F is Faradays constant 9.65 x 104 J
vol-1 mol-1 Em is membrane potential, volts
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Example uptake of NO3- against -0.15 volt
potential ?G zF ?Em ?G (-1)x9.65x104 J
Volt-1 mol-1 x (-0.15Volt) 1.45 x 104 J
mol-1 14.5 kJ mol-1
NO3-
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4. Movement along electrical and concentration
gradients ?G zF ?Em 2.3 RT
log(C2/C1) note rearrangment as ?Em -2.3
RT/zF log(C2/C1) R 8.314 J mol-1 K-1 z is
charge of solute F is Faradays constant 9.65 x
104 J vol-1 mol-1 Em is membrane potential,
volts
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Enzyme kinetics What are enzymes? What kinds of
molecules are they made of? What do they do to
reaction rates? How do they work? Whats the
worlds most abundant enzyme? What conditions
affect the rate of enzyme-catalyzed reactions?
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Vmax
reaction rate, V (moles of product per second)
Substrate concentration, S (moles/liter)
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Vmax
V
1/2 Vmax
Michaelis-Menten equation
Km
S (substrate concentration)
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Enzyme specificity is not perfect, other
molecules can compete for the active
site. competitive inhibition Enzyme
structure can be modified by other
molecules, reducing enzyme activity. non
competitive inhibition
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No inhibitor
With competitive inhibitor
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• Conditions affecting enzyme activity.
• 1. pH
• Enzymes have an optimum pH at which activity is
  maximum,
• with sharp declines in activity at lower and
  higher pH.
• pH affects enzyme activity by altering ionization
  state of active site or by
• affecting the 3-D conformation of the active
  site.
• 2. Temperature
• Enzyme activity has an optimum temperature, with
  sharp declines in
• activity at lower and higher pH.
• Reaction rates increase with temperature because
  enzymes and reactants
• are moving faster and have higher probability of
  encountering one another.
• Enzyme activity decreases at temperatures high
  enough to cause
• denaturation, the unfolding of protein
  structure and loss of proper
• conformation for catalysis.