Transcript Energy - The Virtual Plant

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• Energy
 Why cells need energy
– driving energetically unfavourable reactions
– the need for electron and energy transfer
 The laws of thermodynamics (Freeman Chp2, 32 – 37)
 Endothermic and exothermic reactions (Freeman Chp 2, 32 – 37)
 Photosynthesis and respiration as endothermic and
exothermic reactions
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Why do cells need energy?
1. to drive energetically unfavourable reactions
2. to balance the need for electron and energy transfer
Energy
Reactants
Products
Electrons
Other reactions produce energy
Energy
Products
Reactants
Electrons
These reaction are governed by the laws of thermodynamics
defining energy:
1. Energy is the capacity to do work and exists as potential energy or
kinetic energy.
2. When it is actively involved in reactions this potential
energy is converted into kinetic energy altering chemical
bonding of other molecules
3. For example, the molecule ATP (adenosine
triphosphate) has potential energy stored in its
molecular structure.
The first law of thermodynamics states that energy can never be
destroyed but can be transformed from one type to another – as
in the ATP example above.
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2
Ep
Ek
Ep(lower)
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What determines if a reaction will require or produce energy?
•
Reaction will be spontaneous (exothermic) if the potential energy of
the products is lower than that of the reactants.
• Reaction will be spontaneous (exothermic) if the resultant products are
less ordered that the reactants
Second law of thermodynamics: reactions proceed to
maximise entropy and minimise potential energy,
order leads to disorder…..
2nd Law of Thermodynamics
order
--
disorder
gives off energy
disorder ----
order
requires energy
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Gibbs free energy change = change in potential energy + change in entropy
DG = DH
+ TDS
T is temperature in Kelvin
as entropy directly related
to temperature
Decrease in potential energy & increase in entropy = exothermic, spontaneous
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Increase in potential energy & decrease in entropy = endothermic, not spontan
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Some reactions also involve the transfer of electrons
These are referred to as redox reactions
• Atom that loses electron(s) is oxidised.
• Atom that gains electron(s) is reduced.
2e’
H+
reductant
1st and 2nd laws of thermodynamics apply to redox reactions
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Respiration
Energy
Complex
Simple
Carbohydrates (e.g. glucose C6H12O6)
Reduced
CO2
Oxidised
Electrons
Exothermic – releases energy and/or electrons
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Photosynthesis
Energy
Simple
Complex
Carbohydrates (e.g. glucose C6H12
CO2 + H2O
Oxidised
Reduced
Electrons
Endothermic – requires energy and/or electrons
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It’s more complex than this!
Respiration overall is exothermic, but some of the
reactions are endothermic (require energy).
Photosynthesis overall is endothermic, but some of the
reactions are exothermic (produce energy).
 Energy and Electron carriers in biological systems
 Enzymes (Freeman, Chpt 3, p 63-71)
 Phosphorylation (Freeman, Chpt 9, p 177- 181)
 Overview of respiration (Freeman, Chpt 9)
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Energy and Electron carriers in biological systems:
Metabolism requires the exchange of:
• Energy
• Electrons
• Simple carbon units
Energy
Decrease in entropy & increase in potential energy
glucose + phosphate  glucose-6-phosphate
Requires 14 kJ mol-1
O
HO— P — OOH
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Glucose + phosphate + energy  glucose-6-phosphate + spent
supplier
energy
supplier
Re-energized
Adenosine triphosphate
Acid anhydride
bond
3
31 kJ mol-1
3
14 – 32 = -17 kJ mol-1
Glucose + phosphate + ATP  glucose-6-phosphate + ADP
Heat
3
Related compounds power some biosynthetic pathways:
GTP – Guanosine triphosphate
UTP – Uridine triphosphate
CTP – Cytidine triphosphate
ATP
GTP
3
Acid anhydride bonds of ATP are made:
• by the light reactions of photosynthesis
• respiration
Adenosine
triphosphate
ATP
Energy
31 kJ mol-1
Phosphorylation
De-phosphorylation
Energy
-31 kJ mol-1
Adenosine
diphosphate
ADP + Pi
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Phosphorylation accomplished in two ways:
• substrate phophorylation
• via electron transport and ATPsynthase (enzyme)
Adenosine
triphosphate
Adenosine
diphosphate
ADP + Pi
Phosphorylation
Inorganic
phosphate
Acid anhydride bond
ATP
vocabulary Resp 2
entropy
order
disorder
thermodynamics
energy (heat)
energy (biolocical)
endothermic
exothermic
phosphorylation
dephosphorylation
oxidation
reduction
redox