An Introduction to Metabolism

Page
6

Cytoskeletal track

Motor protein

Protein moved

(a) Transport work: ATP phosphorylates

transport proteins

ATP

ATP

Slide 45

The Regeneration of ATP

ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP)

The energy to phosphorylate ADP comes from catabolic reactions in the cell

The chemical potential energy temporarily stored in ATP drives most cellular work

Slide 46

Fig. 8-12

P

i

ADP

+

Energy from

catabolism (exergonic,

energy-releasing

processes)

Energy for cellular

work (endergonic,

energy-consuming

processes)

ATP

+

H2O

Slide 47

Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers

A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction

An enzyme is a catalytic protein

Hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction

Slide 48

Fig. 8-13

Sucrose (C12H22O11)

Glucose (C6H12O6)

Fructose (C6H12O6)

Sucrase

Slide 49

The Activation Energy Barrier

Every chemical reaction between molecules involves bond breaking and bond forming

The initial energy needed to start a chemical reaction is called the free energy of activation, or activation energy (EA)

Activation energy is often supplied in the form of heat from the surroundings

Slide 50

Fig. 8-14

Progress of the reaction

Products

Reactants

∆G < O

Transition state

Free energy

EA

D

C

B

A

D

D

C

C

B

B

A

A

Slide 51

How Enzymes Lower the EA Barrier

Enzymes catalyze reactions by lowering the EA barrier

Enzymes do not affect the change in free energy (∆G); instead, they hasten reactions that would occur eventually

Animation: How Enzymes Work

Slide 52

Fig. 8-15

Progress of the reaction

Products

Reactants

∆G is unaffected

by enzyme

Course of

reaction

without

enzyme

Free energy

EA

without

enzyme

EA with

enzyme

is lower

Course of

reaction

with enzyme

Slide 53