Lecture #7

Introduction to Metabolism

&

Enzymes

Energy

• the capacity to cause change

• the ability to do work

• Kinetic Energy

• Thermal energy

• Potential Energy

Thermodynamics

• The study of energy transformations that occur

• Law #1 – Energy can neither be created nor destroyed; it can only be transferred and transformed

Chemical Potential Energy

A + B ↔ C + D

The potential energy available for release in a chemical reaction

Potential energy - stored energy that can be used to transfer energy from one system to another

G and G

• Gibbs free energy - the energy portion of a system available to do work – when temperature and pressure are constant

• G – the change in free energy that happens when a system changes

G = Gend – Gstart

What G means….

A + B ↔ C + D if G is negative – the ending free energy is

lower than the starting free energy therefore, there has been a release of energy –

energy must have been transferred or transformed – spontaneous reaction

If G is positive – the ending free energy is higher than the starting free energy

Energy is absorbed by the system - non-spontaneous reaction

• Exergonic reaction» energy is released» the G value is less than 0 (negative)» spontaneous» the G value represents the theoretical maximum

amount of work (quantity of energy that can be transferred to another system)

• Endergonic reaction» energy is absorbed and stored» the G value is grater than 0 (positive)» non-spontaneous» the G value represents the amount of energy

required to drive the reaction

Respiration/Photosynthesis

C6H12O6 + O2 ↔ 6CO2 + 6H2O

forward reaction: G = -686 kcal/mol

reverse reaction: G = 686 kcal/mol

Equilibrium

• balance• when a chemical reaction proceeds at the

same rate as its reverse reaction, with no change in the amount of each compound

• lowest possible free energy (G) value• a system in balance cannot spontaneously

change• Must push the system away from the

balance

Equilibrium in Metabolism?

C6H12O6 + O2 → 6CO2 + 6H2O

CO2

O2

C6H12O6

CO2

O2

C6H12O6

C6H12O6 + O2 → 6CO2 + 6H2O

ATP

ATP ADP

P

Pi

G=-7.3 kcal/mol

Ca2+-ATPase – skeletal muscle

CYTOPLASM

ER LUMENCa2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+ Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+ Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+ Ca2+

ATP

Ca2+

P

Enzymes

• a protein catalyst

• catalyst – speeds up a chemical reaction

E + S ↔ ES ↔ E + P

E + S ↔ ES ↔ E + P

E + S ↔ ES ↔ E + P

• Continued tomorrow and in today’s lab session……..