CHAPTER 6-METABOLISM, ENERGY AND ENZYMES
I. METABOLISM-the total of all of the reactions that occur in a living organism.
A. This includes those reactions that generate energy, breakdown large molecules and
remove wastes from the organism.
B. Anabolic vs. Catabolic Reactions
II. ENERGY-the capacity to do work or the ability to bring about a change.
A. Important Terms That Relate to Energy
1. Work-the movement of an object against a force.
2. Thermodynamics-the study of the relationships among different forms of energy.
3. Kinetics-the study of the rates of reactions.
4. Calorie-the unit that is used to measure energy.
5. Activation Energy-the energy required for a reaction to occur.
B. Types of Energy:
1. Potential Energy-
2. Kinetic Energy-
C. The Laws of Thermodynamics
1. The First Law of Thermodynamics-states that energy is neither created nor destroyed.
a. This law actually tells us that the total amount of energy in any process
remains constant.
b. Essentially, this Law states that
2. The Second Law of Thermodynamics-states that in any process, the energy available
for work decreases over time. Energy tends to spread out over time.
a. In other words, the amount of disorder in a system increases over time.
b. Entropy-
1) With regards to entropy, this Law states that
III. CHEMICAL REACTIONS-reactions between different atoms and molecules. These reactions usually
produce stable atoms.
A. Most chemical reactions are involved in energy transfers (generating and using energy).
B. Set-up of a Typical Chemical Reaction:
C. Types of Chemical Reactions-based on energy flow:
1. Exergonic Reactions-“energy-releasing reactions.”
a. In these reactions, the reactants have more energy than the products.
b. These reactions are described as being spontaneous. What does this mean?
c. What happens to energy in these reactions?
2. Endergonic Reactions-“energy-consuming reactions.”
a. In these reactions, the products have more energy than the reactants.
b. These are not spontaneous reactions.
c. What must happen for these reactions to occur?
D. Specific Types of Chemical Reactions
1. Synthesis Reactions-
2. Decomposition Reactions-
3. Exchange Reactions-
4. Reversible Reactions-
5. Oxidation/Reduction Reactions-
IV. METABOLIC PATHWAYS-sets of reactions that are influenced and governed by enzymes.
A. These build up and breakdown large molecules.
B. Examples of Metabolic Pathways:
V. ENZYMES-proteins that increase the speed of biological reactions.
A. Characteristics of Enzymes:
1. They are classified as catalysts2. They function by lowering the activation energy of molecules. Without enzymes,
reactions would proceed at a very slow rate.
3. Enzymes are specific4. Most enzymes end in –ase.
5. Enzymes are not changed in the reactions that they influence.
6. Enzymes regulate processes that:
B. Basic Structure of an Enzyme
1. They are protein in composition.
2. Every enzyme has an active site-this is the site on the enzyme where the reaction
occurs.
3. Substratea. Substrates attach to the active site of the enzyme.
b. The active site of an enzyme has a specific shape. The active site will only
“fit” a certain molecule. The only molecule that will fit into the active site is
the molecule that the enzyme reacts with. This gives an enzyme its specificity.
4. The Induced Fit Model of Enzyme Activity-describes how an enzyme functions.
C. Factors That Influence Enzyme Activity
1. Temperature
a. Enzymes work best at temperatures between:
b. Extreme temperatures can denature enzymes. What does this mean?
c. A few organisms (primarily bacteria) have enzymes that can function outside
of the above temperature range. These bacteria can live in hot water vents and
other harsh environments.
2. pH
a. Most enzymes work best at a pH value of
b. Extreme pH values can denature enzymes.
c. Pepsin1. This enzyme functions by
2. It works best at a pH of
3. Salts
a. In general, enzymes do not function when salt concentrations are high. Once
again, high salt concentrations denature enzymes.
b. Can you think of a situation where salt is useful to humans because it slows the
activity of enzymes?
D. Regulation of Enzyme Activity
1. Enzymes are turned on by the presence of their specific substrate.
2. Enzymes are turned off by Inhibitors. Inhibitors are defined as molecules that prevent
an enzyme from catalyzing a reaction.
a. Types of Inhibitors
1) Steric Inhibitors-block the active site of the enzyme. How does this
serve to inhibit enzyme activity?
2) Allosteric Inhibitors-attach to areas other than the active site of an
enzyme. In this case the allosteric inhibitor changes the shape of the
enzyme, including the active site. Due to this, the substrate cannot
attach to the enzyme.
E. Coenzymes-non-protein, organic molecules that aid enzymes in influencing reactions.
1. What are some important coenzymes?
VI. ADENOSINE TRIPHOSPHATE (ATP)A. All living organisms have the ability to breakdown sugars to produce ATP.
B. ATP is composed of:
1. Adenine
2. Ribose
3. 3 Phosphate groups-the energy associated with ATP is stored in these bonds. When
these phosphate bonds are broken, a small amount of energy is released. Cells can use
this energy for a variety of tasks.
a. The removal of a phosphate group from ATP produces a molecule known as
C. The ATP/ADP Cycle
1. Diagram:
2. Phosphorylation-