Transcript Energy and Metabolism

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 Earth
Energy 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
Thermodynamics = branch of chemistry
concerned with energy changes
Energy = capacity to do work
Energy exists in 2 states:
kinetic energy
potential energy
Energy may take many forms: mechanical, sound, light,
electrical, heat
Fig. 6.1
Potential energy and kinetic energy
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
There are millions of biological
examples of potential/kinetic
energy
Identify several:
The most convenient measure of
energy is heat
• Heat capacity (energy content) of
biomolecules (sugars, proteins, lipids) is
expressed in Calories (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!!
Without constant inflow of solar
energy, life as we know it, would
not exist
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
Fig. 6.4
Fig. 6.6
ATP:
The energy
currency of
the cell
Fig. 6.7
ATP cycles continuously
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
Model of enzyme activity
Re: enzymes are re-useable!!
RE:
Factors affecting enzyme activity
• Heat and pH
• Substrate concentration
• Enzyme inhibition:
• Competitive inhibition
• Non-competitive inhibition
• Biofeedback inhibition
Biofeedback inhibition
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