An Introduction to Metabolism

Page
10

(isoleucine)

Enzyme 5

Intermediate D

Intermediate B

Intermediate A

Enzyme 4

Enzyme 2

Enzyme 3

Initial substrate

(threonine)

Threonine

in active site

Active site

available

Active site of

enzyme 1 no

longer binds

threonine;

pathway is

switched off.

Isoleucine

binds to

allosteric

site

Slide 76

Specific Localization of Enzymes Within the Cell

Structures within the cell help bring order to metabolic pathways

Some enzymes act as structural components of membranes

In eukaryotic cells, some enzymes reside in specific organelles; for example, enzymes for cellular respiration are located in mitochondria

Slide 77

Fig. 8-23

1 µm

Mitochondria

Slide 78

Fig. 8-UN2

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 79

Fig. 8-UN3

Slide 80

Fig. 8-UN4

Slide 81

Fig. 8-UN5

Slide 82

You should now be able to

Distinguish between the following pairs of terms: catabolic and anabolic pathways; kinetic and potential energy; open and closed systems; exergonic and endergonic reactions

In your own words, explain the second law of thermodynamics and explain why it is not violated by living organisms

Explain in general terms how cells obtain the energy to do cellular work

Slide 83

Explain how ATP performs cellular work

Explain why an investment of activation energy is necessary to initiate a spontaneous reaction

Describe the mechanisms by which enzymes lower activation energy

Describe how allosteric regulators may inhibit or stimulate the activity of an enzyme