UNIT 2: Metabolic Processes
Chapter 3: An Introduction to Metabolism
pg. 124 - 165
3.1: Metabolism and Energy
pg. 126 - 140
All living organisms grow, respond to the environment, and reproduce; to do
this they require energy. To acquire, store, and use energy to perform a
multitude of functions. Cells use ATP molecules to supply the energy, which
are produced in the mitochondria. There are a thousand of chemical
reactions occurring simultaneously. The sum of all anabolic and catabolic
reactions is called metabolism.
Metabolism – is the sum of all chemical reactions in a cell or organism.
Energy and the Ability to Do Work
Energy – the Ability to do Work
Work is performed when energy is used to move an object over a distance.
At a biochemical level, the bonding of atoms, molecule, and compounds, or
break them down is work. Moving materials across the cell membrane by
active transport requires energy, and work is being done.
Work – force x distance.
Energy comes in many forms; chemical, electrical, mechanical, light, and
thermal. Each form of energy can be transformed into another form. The
lowest form of energy is thermal which is lost to the atmosphere as waste
energy. Photosynthesis converts light energy into chemical potential energy.
Kinetic Energy and Potential Energy
All energy exists in one of two states; kinetic or potential.
Kinetic energy – is the energy of motion.
Potential energy – is the store energy that an object possesses as a result of
its position relative to other objects or to its internal structure.
Figure 3: As the ball falls, the gravitational potential energy decreases.
The First Law of Thermodynamics
First Law of Thermodynamics – is a principle that states that energy can be
transferred or transformed, but it cannot be created or destroyed.
The First Law of Thermodynamics
The total amount of energy in any closed system is constant. Energy
cannot be created or destroyed; it can only be converted from one form to
another. If a physical system gains an amount of energy, another physical
system must experience a loss of energy of the same amount.
When photosynthesis occurs, sunlight light energy is converted to
chemical potential energy. The energy is stored in a carbohydrate
(starch), which in turn is consumed by other organisms. The living
organisms then convert the starch into other forms of energy,
glycogen, which can be used as mechanical energy used for muscle
movement. As a result energy is continuously transformed to
different forms of energy.
Energy and Chemical Bonds
To transform energy into different forms; depends of the breaking and
formation of bonds in chemical reactions. The amount of energy found in
bonds (potential) depends on the location of electrons to the positively
charged nucleus. The further away the electrons are from the nucleus the
greater the amount of energy they have. When an electron is strongly
attracted to two nuclei, a chemical bond is formed.
In a chemical reaction, chemical bonds are broken (reactants) and new
chemical bonds are formed (products). On the reactant side of the equation
energy must be absorbed to break bonds, (electrons move further away from
the nucleus), while on the product side energy is released as new bonds are
created, (electrons move closer to the nucleus).
Bond Energy
Bond energy – is the minimum amount of energy that is required to break a
particular type of bond; measured in KJ/mol of bonds.
See Table 1: Average Bond Energy, pg. 129
Mole – is the number (approximately 6.022 x 1023) of atoms or molecules
whose mass in grams is equal to the atomic mass of one such particle in
atomic mass units; one carbon atom has a mass of 12 AU, and therefore, one
mole of carbon atoms has a mass of 12g.
Activation energy (Ea) – is the minimum amount of energy that chemical
reactants must absorb to start a reaction.
Transition state – is a temporary condition during a chemical reaction in
which the bonds in the reactants are breaking and the bonds in the products
are forming.
Exothermic reaction – is a chemical reaction in which energy is released,
leaving the products with less chemical potential energy than the reactants.
Endothermic reaction – is a chemical reaction in which energy is absorbed,
giving the products more chemical potential energy than the reactants.
The Second Law of Thermodynamics
Second Law of Thermodynamics – is a principle that states that every time
energy is converted to another form, some of the energy becomes unusable.
The Second Law of Thermodynamics
In every energy transfer or conversion, some of the useful energy in the
system becomes unusable and increases the entropy of the universe.
The unusable form of energy is usually in the form of thermal
energy (heat) and is waste energy that increases the entropy of the
universe.
The concept of energy efficiency applies to living organisms; in
cellular respiration glucose is used to form ATP. During this
process only 40% of the potential energy in glucose is used to form
ATP, the rest is lost as thermal energy.
Entropy – is a measurement of disorder in a system.
In the field of thermodynamics, the measure of randomness and
disorder within a system is a measurable quantity called entropy.
All systems in the universe are moving towards disorder or
randomness, and in the measure of randomness in chemical and
physical changes, and are usually associated with a breaking down
of larger molecules (particles) into smaller molecules (particles).
When solutions diffuse, move substances from an area of high
concentration to an area of low concentrations, the substances
become more random.
Entropy increases when;
- solids react to form liquids or gases
- liquids react to form gaseous products
- the total number of product molecules is greater that the
total number of reactant molecules
Spontaneous Change
Spontaneous change – is a change that will, once begun, continue on its
own under a given set of conditions; does not require a continuous supply of
energy.
The burning of a match is a spontaneous change. The match will not burn
until it is struck, but will continue to burn after.
A non-spontaneous reaction will not occur unless there is a continuous input
of energy to maintain the reaction.
Gibbs Free Energy
Free energy – is energy that can do useful work, also called Gibbs free
energy.
The second law of thermodynamics, energy transformation is never 100%
efficient. Some energy is always lost to the environment. The energy that is
not lost or the portion still available to do work is called free energy.
In living organisms, the free energy is responsible for the chemical and
physical processes, the work required in activities, such as; the synthesis of
molecules, reproduction, and movement.
The change in free energy:
∆G = G final state - G initial state
Negative ∆G - reactions occur spontaneously.
Positive ∆G - reactions are non-spontaneous.
Cellular Respiration is an example of a reaction that releases energy.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
∆G = -2870 KJ/mol
Photosynthesis is an example of a reaction that gains energy.
6 CO2 + 6 H2O → C6H12O6 + 6 O2
∆G = +2870 KJ/mol
Exergonic reaction – is a chemical reaction that releases free energy; the
products have less free energy than the reaction.
Endergonic reaction – is a chemical reaction that absorbs free energy; the
products have more free energy than the reactants.
Figure 16 (a) In an exergonic reaction, free energy is released. The products have less free
energy than was present in the reactants, and the reaction proceeds spontaneously. (b) In an
endergonic reaction, free energy is gained. The products have more energy than was present in
the reactants. An endergonic reaction is not spontaneous: it proceeds only if energy is supplied
by an exergonic reaction.
Coupled Reactions
Energy coupling – is the transfer of energy from one reaction to another in
order to drive the second reaction.
Exergonic reactions occur spontaneously, yet endergonic reactions require a
continuous supply of free energy to occur. These reactions are occurring
continuously within the cell; therefore the cell must supply this energy. For
this to happen exergonic and endergonic reactions are coupled together, so
the energy released can be used.
When coupled together the ∆G is still negative.
Exergonic: A → B + C
∆G = -5 KJ/mol
Coupled to;
Endergonic:
D + E → F
Coupled Net Difference:
∆G = +4 KJ/mol
∆G = -5 KJ/mol
∆G = +4 KJ/mol
∆G = -1 KJ/mol
Catabolic pathway – is a pathway in which energy is released and complex
molecules are broken sown into simple molecules.
Anabolic pathway – is a pathway in which energy is supplied to build
complex molecules from simple molecules.