Enzymes and EnergyThis is a featured page

Chapter Objectives

1. state the principles of catalysis and explain how enzymes function as catalysts.
2. explain how the names of enzymes are derived and comment on the significance of isoenzymes.
3. describe the effects of pH and temperature on the rate of enzyme-catalyzed reactions and explain how these effects are produced.
4. describe the roles of cofactors and coenzymes in enzymatic reactions.
5. explain how the law of mass action helps to account for the direction of reversible reactions.
6. explain how enzymes work together to produce a metabolic pathway and how this pathway may be affected by end-product inhibition and inborn errors of metabolism.
7. explain how the first and second laws of thermodynamics can be used to predict if metabolic reactions will be endergonic or exergonic.
8. describe how ATP is produced and explain its significance as the universal energy carrier.
9. define the terms oxidation, reduction, oxidizing agent, and reducing agent.
10. describe the use of NAD and FAD in oxidation-reduction reactions and explain the functional significance of these two molecules.

Enzymes as Catalysts

Enzymes are the biological catalysts that increase the rate of chemical reactions. Most enzymes are proteins, the vast differences in protein structures allow each different enzyme to be specialized in their action.

What is life? What is death? What is illness? What is health? What is youth? What is aging?
How do these questions apply to physiology?

We all could come up with some kind of an answer but, It all comes back to the cellular level. What is taking place in the cells?

Checklist of Enzyme Characteristics

-Enzymes are composed of protein and may require co-factor (metallic ion) or coenzyme (organic molecule, such as a vitamin).
-Enzymes act as organic catalysts to speed up the rate of cellular reactions.
-Enzymes lower the activation energy required for a chemical reaction to proceed.
-Enzymes have unique characteristics such as shape, specificity, and function.
-Enzymes enable metabolic reactions to proceed at a speed compatible with life.
-Enzymes provide a reactive site for target molecules called substrates.
-Enzymes are much larger in size than their substrates.
-Enzymes associate closely with substrates but do not become integrated into the reaction products.
-Enzymes are not used up or permanently changed by the reaction.
-Enzymes can be recycled, thus function in extremely low concentrations.
-Enzymes are limited by particular conditions of temperature and pH.
-Enzymes can be regulated by negative feedback and genetic mechanisms.

What is a Catalyst?How can a bicycle be a catalyst?

We use catalysts often in our daily lives to aid us with whatever it is we may be doing.

-A Catalyst is something that speeds up a reaction.
-It is NOT used up or destroyed during the reaction, so it can be reused again and again!
-It doesn't change the end result of the reaction, it only speeds it up!
-Functionally enzymes are biological catalysts!

-The same reaction would have occurred to the same degree in the absence of the catalyst, but it would have progressed at a much slower rate. In order for a given reaction to occur, the reactants must have sufficient energy. The amount of energy required for a reaction to proceed is called activation energy.

Some examples of active catalysts are:

  • A Wrench: As our wonderful teacher Kevin said, you could try to turn a bolt with your fingers, but it would be very difficult. If you use a wrench, you will be able to get that bolt off, much faster, and you would have to exert a lot less of your own energy!
  • Cars: You could walk to Provo from Salt Lake, it would take hours, maybe days, so you wouldn't do it. You would most likely take a car. You conserve your energy and get to Provo much faster! Your "wonderful teacher Kevin" used a bicycle as an example, and not a car. This was a conscious choice--why might I have thought the bicycle would be a better analogy for a catalyst than a car? (see if you can come up with a reason--I'll post my thoughts at the very bottom of this page)

The Laws of Thermodynamics: A set of universal laws governing all energy changes in the universe
1st Law-Energy cannot be created or destroyed, however it changes forms.
  • Mechanical, sound, light, electric, heat, chemical, etc...
  • All forms of energy can be converted to Heat. (When you convert one form of energy to another form you lose some of the energy to Heat energy)
2nd Law-Disorder is continuously increasing.
  • Entropy is a measure of the disorder of the system.
*It doesn't take energy to go to a state of disorder.

Simply put, the 2nd Law states: Entropy increases. If entropy happens spontaneously how do your cells maintain their level of order and complexity?
Answer:It takes energy!

Complexity requires energy.

Energy of Activation

- The energy required for a reaction to proceed.
- Catalysts lower the activation energy of a reaction and thus increases its rate.
- An enzyme can make a reaction happen about a million times faster! Like a switch!
- Enzymes cannot make an endergonic reaction exergonic.

Energy is defined as the ability to do work.

Here is an example of "Activation Energy":
In this video the match has its own stored energy known as potential energy. The activation energy here would be the laser pointer. We typically light matches with friction or another flame, but this is pretty cool! Check it out!

Types of energy:
Potential Energy: Stored Energy
  • It takes energy to release it.
Kinetic Energy: Energy in Motion

Activation Energy: The amount of action required for a reaction to proceed.
Match analogy: Each match has potential energy, but will not release it until some activation energy has been supplied (either by friction or by heat of an already lit match)

Control of Enzyme Activity

Enzymes have the ability to lower the activation energy of a reaction as a result of their structure. They are large structures with 3-Dimensional shapes. Enzymes are proteins that serve as catalysts and help speed up reactions in cells.

Model of Enzyme Action

What is a substrate?
A substrate is the reactant molecule within an enzyme. Each substrate has a specific shape that allows it to fit into the active site of the enzyme.

How enzymes work:
Enzymes are proteins that serve as catalysts
They speed up chemical reactions within cells
Enzymes bind a specific molecule and stress bonds to make a particular reaction more likely.

Active site
Sites on enzymes surface wherein reactant fits.

Binding site on reactant (substrate) where enzymes binds.

Enzyme shape determines it's activity/changes binding of the substrate.
The image “http://fig.cox.miami.edu/~cmallery/255/255enz/competitive_inhibition.jpg” cannot be displayed, because it contains errors.

Factors affecting enzyme activity
Enzyme activity is affected by any change in condition that alters the enzymes 3-D shape. The structural bonds of enzymes are sensitive to changes in temperature and pH.

How Cells Regulate Enzymes

A cell can control the activity of an enzyme by altering it's shape. Allosteric enzymes have shapes that can be altered, but the binding signal molecules.These molecules bind to the alloster site. Repressors bind and repress enzyme activity. Activators bind and restore or increase enzyme activity.

Enzyme inhibition occurs in two ways:
Competitive inhibition-Inhibitor binds at the enzyme's activity site
Non-competitive inhibition-inhibitor binds at the enzyme's alloster site

Constitutive enzymes- always present always produced in equal amounts or at equal rates regardless of amount of substrate, enzymes involved in glucose metabolism.

2 Types of Metabolism
Anabolism-biosynthesis building complex molecules from simple ones requires energy (in the form of ATP)



Breaking down complex molecules into simpler ones, often used to generate ATP

Synthesis or Condensation Reactions
Anabolic reactions to form covalent bonds between smaller substrate molecules. Requires ATP and releases one molecule of water for each bond. Removes -H from one side and -OH from the other to form H20 (a water molecule).

Hydrolysis Reaction
Catabolic reactions that break down substrates into small molecules, requires the input of water. Adds water to the molecule and splits it into two smaller molecules.

Metabolic Pathways can be linear, branched (divergent or convergent), or cyclic. Many enzymes are present, each one makes a product that becomes a reactant, that is the reactant for the next protein, A to B to C to D etc.


Living organisms require the constant expenditure of energy to maintain their complex structures and processes. Central to life processes are chemical reactions that are coupled, so that the energy released by one reactions incorporated into the products of another reaction. The transformation of energy in living systems is largely based on reactions that produce and destroy molecules of ATP and oxidation-reduction reactions.

Bioenergtics refers to the flow of energy in living systems. Organisms maintain their highly ordered structure and life-sustaining activities through the constant expenditure of energy obtained from their environment.The energy flow in living systems obeys the first and second laws of the physics, which is thermodynamics.

Redox Reaction
This is a simultaneous oxidation-reduction process whereby cellular metabolism occurs, such as the oxidation of sugar in the human body, through a series of very complex electron transfer processes.
The chemical way to look at redox processes is that the substance being oxidized transfers electrons to the substance being reduced. Thus, in the reaction, the substance being oxidized (aka. the reducing agent) loses electrons, while the substance being reduced (aka. the oxidizing agent) gains electrons. Remember: LEO (Losing Electrons is Oxidation) the lion says GER (Gaining Electrons is Reduction).
The term redox state is often used to describe the balance of NAD+/NADH and NADP+/NADPH in a biological system such as a cell or organ. The redox state is reflected in the balance of several sets of metabolites (e.g., lactate and pyruvate, beta-hydroxybutyrate and acetoacetate) whose interconversion is dependent on these ratios. An abnormal redox state can develop in a variety of deleterious situations, such as hypoxia, shock, and sepsis.

Review Questions

1. The amount of energy required for a reaction to proceed is called?
a. enzymes
b. catalysts
c. activation energy
d. cofactors

2. Thermodynamics obeys by which laws?
a. first and third branch
b. first and second branch
c. second and third branch
d. none of the above

3. Which of the following forms does energy exist in?
a. Mechanical, sound, light, electric, heat, chemical
b. Sound, mass, volume, Temperature
c. Light, mechanical, physical, heat, electric
d. Weight, volume, mass

4. Which Statement does not belong in the first Law of Thermodynamics?
a. Energy can change form.
b. During each conversion some energy is lost.
c. Energy is in an ongoing organized motion.
d. Are ya crazy, all of these statements are correct.

5. Which kind of energy uses stored energy?
a. Kinetic Energy
b. Potential Energy
c. Activation Energy
d. Endergonic Energy

6. What is a Catalysts?
a. Enzyme that speeds up a reaction.
b. Protein that speeds up a reaction.
c. Enzyme that slows a reaction.
d. Protein that slows a reaction.

7. What kind of energy can be converted to Heat energy?
a. Mechanical
b. Sound
c. Light
d. Chemical
e. All of the above

8. How do cells regulate enzymes?
a. By killing it
b. By changing its shape
c. By producing different proteins
d. By oxidation

9. What are most enzymes?
a. carbohydrates
b. proteins
c. products
d. none of these.

10. Which of these are the laws of thermodynamics?
a. energy can be transformed.
b. energy can be created and destroyed.
c. the amount of entropy increases in every energy transformation.
d. a and c
e. none of these.

11. What are the 2 types of metabolism?
a. anabolism
b. canabalism
c. catabolism
d. animalism

12. What kind of energy do cells use?
a. chemical
b. heat
c. sound
d. physical

Answer to why I used a bicycle as an example of a catalyst instead of a car: Both bikes and cars speed up the travel, but I didn't use a car because the car itself does work (expends energy), while the bicycle just makes the person's work easier. An enzyme does not do the work itself, but just makes the job easier. No analogy is perfect, but that is why I thought the bike was a closer analogy to an enzyme than a car. ~K

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