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

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 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!!

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:Re: enzymes are re-useable!!

Factors affecting enzyme activity

• Heat and pH

• Substrate concentration

• Enzyme inhibition:• Competitive inhibition• Non-competitive inhibition• Biofeedback inhibition

Biofeedback inhibition

Article Review #3

Schrezenmeir, J. and M. deVrese. 2001. Probiotics, prebiotics, and synbiotics – approaching a definition. Am. J Clin. Nutr. 73: 361-364.

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.