Ground Rules of Metabolism

Chapter 6 Part 2

Types of Metabolic Pathways

A metabolic pathway is any series of enzyme-mediated reactions by which a cell builds, rearranges, or breaks down an organic substance• Anabolic pathways build molecules• Catabolic pathways break apart molecules• Cyclic pathways regenerate a molecule from the

first step

Controls Over Metabolism

Feedback mechanisms can adjust enzyme production, or activate or inhibit enzymes

Regulatory molecules can bind to an allosteric site to activate or inhibit enzymes• Feedback inhibition

Allosteric Control

Animation: Allosteric activation

Animation: Allosteric inhibition

Feedback Inhibition

Animation: Feedback inhibition

Redox Reactions

Oxidation-reduction reactions (paired reactions)• A molecule that gives up or donate electrons is

oxidized• A molecule that accepts or gain electrons is

reduced• Coenzymes can accept molecules in redox

reactions (also called electron transfers)

ATP Synthesis

Coenzymes deliver electrons to electron transfer chains for ATP synthesis

Electron transfer chain• A series of redox reactions in membrane-bound

enzymes or molecules that release energy in small, controlled steps

Fig. 6-17, p. 101

nutrientsEnergy-releasing reactions breakdown

products(carbohydrates, fats, proteins)

ADP + Pi

oxidized coenzymes

(e. g., carbon dioxide; water)

reduced coenzymesATP

molecules of life Energy-requiring reactions

small organic molecules

Key Players in Metabolic Reactions

Animation: Enzymes and activation energy

Animation: Enzymes and temperature

Video: Alcohol, enzymes, and your liver