Chapter 8An Introduction to Metabolism

Metabolism

The totality of an organism’s chemical reactions

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2 types of reactions in metabolic pathways

Anabolic and catabolic Which reactions release energy? Which reactions consume energy? Which reactions break down molecules? Which reactions build up larger molecules? Which reactions are considered “uphill”? What type of reaction is photosynthesis? What type of reaction is cellular

respiration?

Forms of Energy

Contrast kinetic energy with potential energy.

Which type of energy does water behind a dam have? A mole of glucose?

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The free-energy of a reaction tells us whether the reaction occurs spontaneously

What is free energy? What is its symbol?

› Endothermic - absorbs heat, H > 0 › Exothermic - releases heat,H < 0

Reactions can also be classified according to the change in the free energy of the reaction:

› Endergonic - NON-SPONTANEOUS, G > 0 › Exergonic - SPONTANEOUS, G < 0

Cellular Respiration vs Photosynthesis

Is cellular respiration an endergonic or an exergonic reaction? What is ∆G for this reaction?

Is photosynthesis endergonic or exergonic? What is the energy source that drives it?

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ATP powers cellular work by coupling exergonic reactions to endergonic reactions

List the three main kinds of work that a cell does. Give an example of each.

1. Chemical work 2. Transport work 3. Mechanical work

ATP – Adenosine Triphosphate

W

Which bond is likely to break?

ATP

By what process will that bond break? When the terminal phosphate is

broken, a molecule of inorganic phosphate Pi is formed, and energy is ___________?

For this reaction ATP ADP + Pi, ∆G = ?

How ATP Performs Work

What is energy coupling? See Fig. 8.10 In many cellular reactions, a phosphate

group is transferred from ATP to some other molecule in order to make the second molecule less stable. The second molecule is said to be ____________.

Enzymes speed up metabolic reactions by lowering energy barriers

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What is a catalyst? What is activation energy? See Fig.

8.14

Review of energy profile of an exergonic reaction

What effect does an enzyme have on EA?

Is ∆G positive or negative? How is ∆G affected by the enzyme?

Catalysis in the Enzyme’s Active Site

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What is meant by induced fit? Explain how protein structure is

involved in enzyme specificity. Enzymes use a variety of mechanisms

to lower activation energy. Describe four of these mechanisms.

4 Mechanisms

1. acting as a template for substrate orientation

2. stressing the substrates and stabilizing the transition state

3. providing a favorable microenvironment

4. participating directly in the catalytic reaction

Effects of Local Conditions on Enzyme Activity

Many factors can affect the rate of enzyme action. Explain each factor listed below.

A. Initial concentration of substrate B. pH C. Temperature Why can extremes of pH or very high

temperatures affect enzyme activity? Name a human enzyme that functions

well in pH 2. Where is it found?

Effects of Local Conditions on Enzyme Activity

Distinguish between cofactors and coenzymes. Give examples of each.

Compare and contrast competitive inhibitors and noncompetitive inhibitors.

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