An Introduction to MetabolismChapter 6: Special Proteins Called Enzymes

Enzymes are Proteins that Act as Biological Catalysts

S + E S + E ES ES P + E P + E

Metabolism is the totality of an organisms chemical reactionsReactions that

build up things = Anabolic Require input of energy

Reactions that breakdown things = Catabolism Energy is released

Energy is the capacity to do work…Kinetic energy: Energy of motionPotential Energy: Energy stored in

matter that has the capacity to do work.Chemical Potential Energy: A form of

potential energy that is stored within the bonds of a molecule.

Laws that Govern Energy TransformationsFirst Law of Thermodynamics: Energy

can be transferred or transformed, but cannot be created or destroyed

Second Law of Thermodynamics: Every energy transfer or transformation results in increasing disorder of the universe (increasing Entropy)

Only a Portion of the Total Energy of Living Organism is Available to do Useful Work.

ENERGY in a cell

Energy lost to universe as heat, light, etc.

Energy used for cells metabolism

FREE ENERGY (G)

I don’t understand? How do the terms entropy, stability, free energy and spontaneous relate to each other?

If you have a lot of free energy you are ordered (low entropy). You are unstable and you want to release that energy spontaneously.

If have low free energy, you are stable and the system is disordered (high entropy). To become ordered again you need energy Non- spontaneous.

Let’s try these examples…

We can relate these terms mathematically using the Gibbs Equation

G = H G = H – TS– TS

Total energy of the system, not all the energy is available to do work

Energy lost in disordering the Universe as heat

G = G = H – TH – TSS

Let’s examine this equation further…What are some ways that we can have a spontaneous process? G < 0G < 0

G = G = H – TH – TSS

G = H – TSG = H – TSINITIAL

G = H – TSG = H – TSFINAL

G < 0G < 0 Negative,Spontaneous

CHANGE

You could do both at the same time and really

have a low GG

You could lower H

You could raise TS

Endergonic vs. Exergonic reactions

Closed vs. an Open System

All energy from catabolism (breakdown) must be captured in the

form of ATP do do useful work.

The ATP Cycle is the energy currency of the cell… It’s like a battery

+

ATP ADPInorganicphosphate

Energy

Energy

How does ATP perform work?

The ATP Cycle Connects Catabolic Paths with Anabolic Paths