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