energy and metabolism “life = energy transformation” each property by which we define life...
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Energy and Metabolism
“life = energy transformation”
Each property by which we define life (order, growth, repro, responsiveness, internal regulation) requires ENERGY
Deprived of a source of energy, life stops
Energy flow on EarthEnergy flows into our biosphere from the sun, a small portion of which is
captured by plants, algae, and certain PS bacteria
Energy exits the biosphere as HEAT
The flow of energy in living systems
ThermodynamicsThermodynamics = branch of chemistry concerned with energy changes
Energy = capacity to do workEnergy exists in 2 states:
kinetic energypotential energy
Energy may take many forms: mechanical, sound, light, electrical, heat
Potential energy and kinetic energyFig. 6.1
The energy required for the girl to climb the stairs is stored as potential energy; the stored energy is released as kinetic energy as the girl slides down
The most convenient measure of energy is heat
• Heat capacity (energy content) of biomolecules (sugars, proteins, lipids) is expressed in CaloriesCalories (cal)
• The term ‘Joule’ is used in Physics (= 0.239 cal)
• The chemical calorie is different than our dietary “Calorie” (which is actually a Kcal!)
Photosynthesis is a wonderful provider!
• A simple sugar (glucose, fructose, etc.) provides ~700 kcal or energy per mole!
• Photosynthate sugars provide the C skeleton to make:
» Amino acids for proteins» Fatty acid chains and glycerol for lipids
• One mole of lipid (with three 16-C saturated fatty acid chains) yields 2340 kcal!!
The Laws of Thermodynamics
• A set of 2 universal laws govern all energy changes in our Universe– The First Law of Td: Energy cannot be created or
destroyed; it can only change from one form to another
– The Second Law of Td: Concerns energy transformations – in every transformation, some “useable” energy is lost.
Disorder (entropy) constantly increases in the Universe
Free Energy within cells (Gibbs Free Energy)
G = H – TS
Where:
G = energy available within a molecule or molecules entering a rxn
H = the energy contained in all the bonds of the molecule(s)
T = temperature in °Kelvin (°C + 273)
S = energy unavailable due to Entropy
Chemical rxns and Free Energy
ΔG = ΔH – TΔS
The change in Free Energy of a chemical rxn is equal to the change in total bond energy minus Temperature times the change in entropy (order)
ΔG is >0 for endergonic rxns, <0 for exergonic rxns
Enzymes and cellular reactions
• Enzymes aid in bringing together reactants or binding a substrate so that key bonds are broken or formed
Characteristics of enzymes:– Proteins (mostly)– Not altered by the reaction they produce;
recyclable– Specific for the substrate(s) to which they bind– Lower the energy of activation for a rxn
Factors affecting enzyme activity
• Heat and pH
• Substrate concentration
• Enzyme inhibition:• Competitive inhibition• Non-competitive inhibition• Biofeedback inhibition
Article Review #3
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Chandel, N.S. et al. 1997. Cellular respiration during hypoxia. J. Biological Chemistry. 272: 18808-18815.
Amerine, M.A. and R.E. Kunkee. 1968. Microbiology of winemaking. Ann. Rev. Microbiol. 22: 324-339.
Hibberd, J.M. and W.P. Quick. 2002. Characteristics of C4 photosynthesis in stems and petioles of C3 flowering plants. Nature. 415: 451-455.