C H A P T E R
2
Summary of Expectations
Briefly explain each of the following points.
• The laws of thermodynamics govern the flow
of energy in living and non-living systems. (2.1)
• The first law of thermodynamics states: Energy
can neither be created nor destroyed but can
be transformed from one form to another. (2.1)
• The second law of thermodynamics states:
Energy cannot be transformed from one form
to another without a loss of useful energy. (2.1)
• Entropy is a measure of randomness in a
system. (2.1)
• In an endothermic reaction, the reactants
contain less energy than do the products;
therefore extra energy must be added for
the reaction to take place. In an exothermic
reaction, the reactants contain more energy
than do the products; therefore there is a
release of energy. Both reactions require
activation energy to begin. (2.1)
• Enzymes are specialized proteins that catalyze
reactions in cells by lowering the required
activation energy. (2.2)
• Each step of a metabolic pathway, or each
constituent reaction of the pathway, needs
its own specific enzyme. (2.2)
• The induced-fit model describes how an
enzyme binds with its substrate in order
to catalyze a reaction. (2.2)
• The process by which an enzyme binds to a
substrate, facilitates a reaction, releases the
products of that reaction, and then binds to
another substrate (beginning the process anew)
is called the catalytic cycle. (2.2)
• The factors that affect enzyme activity are
temperature, pH, inhibitors, cofactors, and
coenzymes. (2.2)
• There are two kinds of enzyme inhibition —
competitive inhibition and non-competitive
inhibition. (2.2)
R E V I E W
• Cofactors and coenzymes also affect enzyme
activity. They have been used to combat
illness such as cancer and Chronic Fatigue
Syndrome. (2.2)
• The energy released by an exothermic reaction
can be used to drive an endothermic one.
Such a combination of reactions is called
a coupled reaction. (2.3)
• ATP is manufactured by coupled reactions. (2.3)
• ATP is a molecule composed of the sugar
ribose, the base adenine, and three phosphate
groups. It is the common energy currency
in all cells (2.3)
• The energy released from the breakdown of
ATP is used to fuel metabolic reactions. (2.3)
Language of Biology
Write a sentence using each of the following words or
terms. Use any six terms in a concept map to show
your understanding of how they are related.
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metabolism
energy
kinetic energy
potential energy
chemical energy
thermodynamics
system
closed system
open system
laws of thermodynamics
entropy
activation energy
exothermic reaction
endothermic reaction
enzymes
catalysis
oxidative enzyme
hydrolytic enzyme
substrate
metabolic pathway
active sites
• induced fit
• enzyme-substrate
complex
• catalytic cycle
• hydrothermal vents
• inhibitors
• non-competitive
inhibition
• allosteric site
• feedback inhibition
• activators
• allosteric regulation
• competitive inhibition
• cofactors
• coenzymes
• restriction enzymes
• prodrug
• coupled reaction
• ATP
• active transport
• sodium-potassium
pump
UNDE RSTAN DIN G CON CEPTS
1. How do living things use energy?
2. Identify two different forms of energy.
3. Energy cannot be created or destroyed, but it
can be transformed. Outline the flow of energy
through living things on Earth.
4. How is an open system different from a closed
system?
5. What is the catalytic cycle?
6. How is activation energy important in
understanding chemical reactions?
Chapter 2 Enzymes and Energy • MHR
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7. How do enzymes affect the rate of biological
reactions?
8. How is an endothermic reaction different from
an exothermic reaction?
9. Energy flows through living things, but matter
is cycled. What does this mean? Explain
briefly.
10. Distinguish between hydrolytic and oxidative
enzymes.
15. Metabolic inhibition can reduce the waste
of energy in a cell. Explain how energy is
transformed in a metabolic pathway and how
stopping the process conserves energy.
16. What is a competitive inhibitor?
17. Describe how allosteric regulation controls
enzyme activity.
18. Identify one cofactor and one coenzyme.
11. What is a thermostable enzyme?
19. Describe how snake venom can affect cellular
processes in the human body.
12. How do amino acid R-groups in enzymes affect
chemical reactions?
20. How do cofactors and coenzymes contribute to
cell processes?
13. Identify two environmental factors that affect
the ability of a protein to catalyze a reaction.
21. How does a coupled reaction use energy?
14. How can an enzyme be regulated with an
inhibitor?
22. Why is ATP an effective energy transfer
molecule in the cell?
23. List three uses for ATP in cells.
24. Why does active transport require energy?
IN QU IRY
25. Within the cell, some thermal energy released
from chemical reactions causes convection of
the cytosol. Design a model of a cell and cell
contents to investigate how thermal energy
within the cell affects the rate of enzyme
reactions in the cell.
26. The enzyme lactase breaks down milk sugar
(lactose) into glucose and galactose. Is this
enzyme hydrolytic or oxidative? Use molecular
model kits to demonstrate your choice.
27. Photosynthesis is an endothermic reaction
that is affected by the temperature in the
environment. Develop a testable hypothesis
that explores how temperature affects
photosynthesis.
28. Which process produces more thermal energy,
photosynthesis or respiration? Design an
experiment to explore this question.
60
MHR • Unit 1 Metabolic Processes
29. Students studied the effectiveness of an enzyme
at different temperatures by determining the
concentration of product after equal elapsed
times. The data table shows their results.
(a) Make a graph using these values.
(b) Interpret the graph to predict the
concentration of the product at 47°C
and 80°C.
(c) At what temperature does the enzyme
function best? Explain your reasoning.
Temperature (°C)
Concentration of product (µg/L)
24
5
27
6
30
8
32
10
35
15
36
18
40
11
45
9
50
4
60
0
COMMU N ICATIN G
30. Earth is an open system for energy but a closed
system for matter. Explain what this means in
terms of cell processes.
31. In the ATP cycle, the breakdown of glucose is
coupled to the buildup of ATP. Use words and
diagrams to describe this process in terms of
stored energy, free energy, and thermal energy.
32. Energy flows through living things, but matter
is cycled. Explain how enzymes demonstrate
efficient use of matter in the cell.
33. Make a flip-book animation to show the
induced fit of a substrate on an enzyme’s
active site.
34. Enzymes are generally substrate-specific.
However, some enzymes can catalyze the
reactions of a family of substrates. Use
diagrams to show how an enzyme could be
specific to two substrates that are similar yet
different in structure.
(b) are affected by a decrease in pH.
36. This diagram shows the metabolic pathway
used by eukaryotic cells to break down
proteins. Ubiquitin is a polypeptide chain that
joins to certain proteins. Existing enzymes can
break down the protein when ubiquitin is
connected.
(a) How is this pathway energy-efficient?
(b) Ubiquitin prepares the protein for the
enzyme. How does adding ubiquitin change
the protein?
ubiquitin
polypeptide
added
protein
to be
degraded
protein
fragment
protein-ubiquitin
complex
enzymes break
protein into
fragments
35. Make a diagram of a polypeptide chain of five
amino acids to explain how R-groups:
(a) interact with a substrate, and
ubiquitin
polypeptide
released
protein
fragment
M A KIN G CON N ECTION S
37. Is a cell a closed system or an open system?
Justify your response.
38. About 95 percent of the electric energy
supplied to an incandescent light bulb is lost
as waste thermal energy. If this were a
biological reaction, how would an enzyme
affect the use of energy?
39. Glucose is one of the products of
photosynthesis. Glucose can also be produced
artificially, but in this case both optical isomers
are produced (that is, left-handed and righthanded glucose). Explain how biological
enzymes produce only one isomer.
40. Milk is heated when it is pasteurized. The
pasteurization process involves heating milk to
kill bacteria without denaturing the milk itself.
In Canada, milk is heated to 72.8°C for 16 s
and then cooled rapidly to 4°C. Ultra High
Temperature (UHT) milk products can be
heated to 135°C for a shorter period of time,
usually 2–5 s. How is each process beneficial
to the producer and the consumer?
Chapter 2 Enzymes and Energy • MHR
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