An Introduction to Metabolism
Metabolism/Bioenergetics Metabolism: The totality of an organism’s
chemical processes; managing the material and energy resources of the cell
1. Catabolic pathways: degradative process such as cellular respiration; releases energy Exergonic
2. Anabolic pathways: building process such as protein synthesis; photosynthesis; consumes energy Endergonic
Thermodynamics Energy (E): capacity to do work;
Kinetic energy: energy of motion Potential energy: stored energy
Thermodynamics: study of E transformations 1st Law: conservation of energy; E
transferred/transformed, not created/destroyed 2nd Law: transformations increase entropy (disorder,
randomness)
Combo: quantity of E is constant, quality is not
Free energy (G) Free energy: portion of system’s E that can
perform work (at a constant T) Exergonic reaction: net release of free E to
surroundings (ΔG<0) - spontaneous Endergonic reaction: absorbs free E from
surroundings (ΔG>0) – NOT spontaneous
Gibb’s Free Energy Formula
ΔG = ΔH - T ΔS ΔG = Gibb’s Free Energy, the amount
of free energy available to a systemUnit = kJ (kiloJoules)
ΔH = heat of reaction (or Enthalpy), the amount of heat energy in a systemUnit = kJ (kiloJoules)
T = temperatureUnit (Kelvin ̊C + 273)
ΔS = entropy, the amount of order/disorder in a systemUnit = J/K (Joules per Kelvin)
What it means ΔG – positive vs. negative
+ ΔG = reaction is endergonic (energy must be supplied to make the reaction occur)
- ΔG = reaction is exergonic (generally, this reaction is spontaneous and releases energy)
ΔH – positive vs. negative + ΔH = reaction is endothermic (heat energy
is absorbed from the surrounding area) - ΔH = reaction is exothermic (heat energy is
released into the surrounding area)
What it means ΔS – positive vs. negative
+ ΔS = the entropy of the system in increasing (you have more free moving molecules, things are breaking apart, catabolism)
- ΔS = the entropy of the system is decreasing (you have more structured arrangement of molecules, tends to be fewer, more complex, molecules, anabolism) EXAMPLE: HC2H3O2 has less entropy than 2 H+
(more number of molecules as opposed to just more atoms in molecule)
EXAMPLEA biological reaction has an
exothermic reaction (ΔH) that produces -55.8kJ of energy. If the reaction is decreasing entropy (ΔS) by -0.35kJ/K at a temperature of 25°C, what would be the free energy (ΔG)? Is this reaction exergonic (releasing energy) or endergonic (absorbing energy)?
SOLUTIONΔG = ?ΔH = -55.8kJΔS = -
0.35kJ/KT = 25°C
= 298K
ΔG = ΔH – TΔS ΔG = -55.8kJ –
(298K)(-0.35kJ/K) ΔG = -55.8kJ +
104.3kJ ΔG = +48.5kJ NOTE: The
reaction is endergonic
QUESTIONSHow do you think the following
affects Free Energy? Does it make it more likely to happen or less likely?
1.Increasing the temperature of a system?
2.Decreasing the entropy?3.Decreasing the enthalpy (heat of
reaction)?
ENERGETICS AND REACTIONS
All reactions need energy to start (Energy of activation)
Many times this energy cost is insurmountable
Strategies to deal with energy cost Couple reaction with another exergonic
reaction Enzymes to reduce energy of activation
Energy Coupling & ATP
E coupling: use of exergonic process to drive an endergonic one (ATP)
Adenosine triphosphate ATP tail: high negative
charge ATP hydrolysis: release of
free E Phosphorylation
(phosphorylated intermediate): enzymes KINASES
Enzymes: LOCK AND KEY MODEL Catalytic proteins:
change the rate of reactions w/o being consumed
Free E of activation (activation E): the E required to break bonds
Substrate: enzyme reactant
Active site: pocket or groove on enzyme that binds to substrate
Induced fit model
Effects on Enzyme Activity
TemperaturepHCofactors:
inorganic, nonprotein helpers; ex.: zinc, iron, copper
Coenzymes: organic helpers; ex.:
vitamins
Rate of enzyme activity There are many actions that can speed up the
rate of enzyme activity (already discussed) Optimal pH, increased temp, increased amount
of enzyme, increased amount of substrate Regardless of optimal concentrations, thing
always limits the enzyme rates Amount of enzyme Once you have “maxed” out the use of
enzymes, the rate of reaction is constant
Enzyme Inhibitors
Irreversible (covalent); reversible (weak bonds)
Competitive: competes for active site (reversible); mimics the substrate
Noncompetitive: bind to another part of enzyme (allosteric site) altering its conformation (shape); poisons, antibiotics