MetabolismThemodynamics

Metabolism = ‘change’Refers to all the chemical reactions that

change or transform matter and energy in cells

Metabolic Pathway = a sequential series of chemical reactions in living cells

energy in energy in

Anabolic Pathway

How can we define energyEnergy = the capacity to do work

Kinetic – energy due to movement (e.g. flowing water)

Potential – stored energy (e.g. A boulder perched on top of a hill)

Chemical energy is potential energy stored up in the bonds of a molecule.

Types of EnergyMechanical energy is the energy found in the

motion of objects.Chemical is the energy contained within the

bonds that hold atoms together to form molecules

Radiant the source of energy for all living things, derived from the sun

All these types of energy may be found in actualized form such as kinetic energy of a falling stone, or in potential form energy stored in objects at rest.

Laws of ThermodynamicsThermodynamics – the science that studies the transfer and transformation of thermal

energy (heat)

First Law of Thermodynamics Take a guess – this law concerns the amount of

energy in the universe

The total amount of energy in the universe is constant.

Energy cannot be created or destroyed, but it can be transformed from one type into another and

transferred from one object to another.

Second Law of Thermodynamics

During any process, the universe tends toward disorder (i.e., entrophy increases).

entropy – a measure of randomness / disorder

greater entropy = greater disorder

metabolise glucose into CO2 and H2O

C6H12O6 + O2 CO2 + H2O + energy

Thermodynamics• In living systems, the primary potential energy

source is chemical energy• Bond energy is a measure of the stability of the

covalent bond between atoms and is measured in kilojoules(kJ)

• It is the amount of energy required to break one mole of bonds between two atoms and is also equal to the amount of energy released when that bond is formed.

• E.g. the C – C bond requires 346kJ/mol. to break it apart, C = O bond requires 799kJ/mol to break

Bond EnergiesMeasured in kJ / mol

(kilojoules per mole)

Double bonds require more energy to break than single bonds

The greater the bond energy, the more stable the bond.

Bond Type Average Bond Energy (kJ/mol)

H-H 436

C-H 411

O-H 459

N-H 391

C-C 346

C-O 359

C=O 799

O=O 494

Bond Energies and Thermodynamics• During chemical reactions, the reactants

molecules must first be broken apart and then the product molecules must be formed.

• When energy or heat is applied to the reactant molecule, the bonds will absorb the energy until they weaken and break apart.

• If a chemical reaction releases more heat than it uses, it is called an exothermic reaction

• If more heat is absorbed into the system than is actually released at the end of the reaction, it is referred to as an endothermic reaction.

Bond Energiesexothermic reactions – energy released

endothermic reactions – energy absorbed

energy is required to break bondsenergy is released to form bonds

breaking > forming

breaking < forming

endothermic

exothermic

Potential Energy DiagramEXOTHERMIC REACTION

Potential Energy Diagram

Gibbs Free Energy

We can measure the amount of energy actually available to break and subsequently form other chemical bonds = free energy of the molecule

Free energy (G) = energy that can do workNote: heat is “useless” as it dissipates

DG = Gfinal – Ginitial

Gibbs Free Energy

DG = Gfinal – Ginitial

Change in free energy can be used to predict whether a chemical reaction is spontaneous or not

When: DG is negative – reaction can proceed

spontaneously = exergonic reaction, products contain less free

energy (lower bond energies) than reactantsGreater disorder

Gibbs Free Energy

DG = Gfinal – Ginitial

Change in free energy can be used to predict whether a chemical reaction is spontaneous or not

When: DG is positive – reaction is non-spontaneous

Endergonic rx - requires an input of energyProducts contain more free energy (higher bond

energies) than reactantsLower disorder in system

Gibbs Free EnergyExergonic reaction – spontaneous, - DG

Endergonic reaction – not spontaneous, + DG

C6H12O6 + 6O2 6CO2 + 6H2O DG = -2870 kJ/mol

6CO2 + 6H2O C6H12O6 + 6O2 DG = +2870 kJ/mol

Potential Energy Diagram

DG

Equilibrium

Equilibrium reactions convert back and forth with minimal energy.

For equilibrium reactions: DG = 0

What is a cell’s main source of energy?

Driving Endergonic Reactions Couple to an exergonic reaction

Example:1. Flow of a solute down its concentration

gradient2. ATP hydrolysis3. Exergonic redox reactions

Exergonic reaction provides the energy required for the endergonic reaction

Adenosine TriphosphateATP is the primary free energy source for cells

ATP ADP + Pi

+ energy

H2O

DG = -31 kJ/mol

in the cell, DG is closer to -54 kJ/mol

ATPase

ATP MoleculeFree energy is used to do 3 main kinds of work1. Mechanical work such as the contraction of

muscles cells, the flow of cytoplasm or the movement of chromosomes during cell reproduction

2. Transport work such as the pumping of substances across membranes against the concentration gradient

3. Chemical work such as synthesizing complex molecules from simpler atoms

The immediate source of energy that powers these cellular processes is ATP

ATP – adenosine triphosphateComposed of the nitrogen base adenine

bonded to the 5-carbon sugar, ribose which is in turn bonded to 3-phosphate groups

The phosphate tail is unstable, and the bonds between the last phosphate groups can be broken

When the bond is broken, a molecule of inorganic phosphate is removed from ATP and it becomes ADP

Adenosine Triphosphate (ATP)

The ATP Molecule

The ATP/ADP Cycle