Energy and life 1 st law of thermodynamics: Law of Conservation of Energy. Energy cannot be created or destroyed hen why do we talk about the “energy crisis?” hat does it mean to be phototrophic vs chemotrophic? (Light as energy source vs chemical energy source) hat does ATP synthetase or photosynthetic reaction center do? hapter 8: Energy, enzymes, and regulati
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Energy and life 1 st law of thermodynamics: Law of Conservation of Energy. Energy cannot be created or destroyed Then why do we talk about the “energy.
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Energy and life
1st law of thermodynamics:Law of Conservation of Energy.
Energy cannot be created or destroyed
Then why do we talk about the “energy crisis?”What does it mean to be phototrophic vs chemotrophic?
(Light as energy source vs chemical energy source)What does ATP synthetase or photosynthetic reaction center do?
Chapter 8: Energy, enzymes, and regulation
Energy transduction
Enzymes can convert one form of energy into another form.* Examples?
Myosin in muscle:
ATP synthase:
Flagellum:
Photosyntheticreaction center:
Electron transfer chainin mitochondria:
chemical to mechanical energy
transmembrane gradient into chemical energy
transmembrane gradient into motion
light into transmembrane gradient
chemical energy into transmembrane proton gradient
2nd law of thermodynamics: entropy (disorder) of an isolated system always increases
Is a living organism in a relatively low or high state?How to grow from a seed or an embryo to an adult organism? Decrease in entropy?
Entropy:
A measure of the randomness or disorder of a system
The greater the disorder the greater the entropy
Energy = The capacity to do work or to cause particular changes.
Chemical work
The synthesis of complex biological molecules from simpler precursors
Mechanical work
Changing the location of organisms (e.g., flagellum), cells and structures within cells
Transport work
The ability to transport molecules against a concentration gradient (uptake of nutrients, elimination of waste, maintenance of ion balance)
Efficiency of energy conversion?
Less than 100%. Question: Where does the rest go?
Heat: thermal motion of molecules without (strong) thermal gradient. It is often difficult to capture this form of energy for doing work
Idea: Eventual thermal death of the universe. Is being debated.
Bottom line for biology: living systems need input of energy to keep functioning. Question: what is the overall energy source driving the biosphere on earth?
Sun light: photosynthesis
G = H - TS
G = change in free energy (amount of energy available to do work)
Describes direction of spontaneous processes. Reactions with a negative G value will occur spontaneously
H = change in enthalpy (heat content)
T = temperature in Kelvin (C + 273)
S = change in entropy
Free energy G and chemical reactions
Standard free energy (G )and the equilibrium constant
When G is determined under standard conditions of concentration, pressure, and temperature the G is called the standard free energy change (G)
If the pH is set to 7, the standard free energy change is indicated by the symbol G´
A + B ⇄ C + D Keq = [C] [D] / [A] [B]
G´ = -RT ln Keq
Reactions proceed in the direction of negative G´
Reaction will proceedto the right (downhill process)
Reaction will proceedto the left (uphill process)
Key issue: how can cells achieve essential reactions with a positive G´?
By coupling an uphill process to a downhill process
A major role of ATP is to drive otherwise endergonic reactions
This makes the overall reaction downhill, so it will proceedFree energy input is needed to sustain life and growthMain downhill processes? ATP hydrolysis and proton motive force
Energy cycle
Note: this is simplification, because it ignores coupling of proton motive force to all three forms of work
Adenosine 5´-triphosphate (ATP)
ATP serves as the major energy currency of cells
“Contains 2 high energy bonds”. Note: there is nothing particularly special about these two bonds except that cells happen to use them.
ATP ADP + Pi + Energy
Pi = orthophosphate
Note: ATP is complexed to Mg2+
Oxidation-reduction reactions
Oxidation-reduction reactions are key in almost all energy metabolism of life (respiration, photosynthesis, and also fermentation, glycolysis):
Coupled to the generation of ATP, proton motive force.
Loss of electrons is oxidation (LEO)
Gain of electrons is reduction (GER)
Aerobic respiration is when O2 acts as the final electron acceptor (O2 H2O)
Acceptor + ne- donor, n = number of electrons transferred⇄
Quantifying redox reactions1. Split redox reactions into two half reactions involving two redox pairs.Example: Fe3+ + Cu+ Fe2+ + Cu2+