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Chapter 7 – Metabolism: Transformations and Interactions
Learning Objectives
After completing Chapter 7, the student will be able to:
1. Discuss the chemical reactions that occur within the body, including metabolism, anabolism, and catabolism.
2. Describe how carbohydrates, proteins, and fats are used to meet the energy needs of the body.
3. Explain the process of glycolysis.
4. Explain the process of deamination and the synthesis of non-essential amino acids.
Assignments and Other Instructional Materials
The following ready-to–use assignments are available in this chapter of the instructor’s manual:
• New! Case study
• Worksheet 7-1: Metabolism Exercises
1
Other instructional materials in this chapter of the instructor’s manual include:
• Classroom activities
• Worksheet answer keys (as appropriate)
Lecture Presentation Outline
4
“Of special interest to…” symbol key: = Hot Topic = Personal Health
= Health Care Professionals = Science Majors
Key to instructor resource annotations (shown to the right of or below outline topics):
PL = Available on Power Lecture DVD-ROM (ISBN 0538797592)
TRA = Transparency acetates: 12e TRA = 12th edition, 11e TRA = 11th edition, 10e TRA = 10th edition
Introductory/whole chapter resources: PL figure JPEGs; Test Bank; IM WS 7-4, CA 7-1, 7-2, 7-3
1
Worksheets 7-1 and 7-5 contributed by Daryle Wane.
2
Contributed by Sharon Rady Rolfes
3
Contributed by Mary A. Wyandt, Ph.D., CHES
4
Contributed by Melissa Langone.
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I. Chemical Reactions in the Body
Plants use the sun’s energy to make carbohydrate from carbon dioxide and water. This is called photosynthesis.
A. Metabolic reactions take place inside of cells, especially liver cells. 10e TRA 66, 67, 68, 69
B. Anabolism is the building up of body compounds and requires energy.
C. Catabolism is the breakdown of body compounds and releases energy. IM WS 7-1, 7-3
D. The Transfer of Energy in Reactions—ATP 12e TRA 14
1. A high-energy compound called adenosine triphosphate (ATP) is made.
1. Enzymes are protein catalysts that cause chemical reactions.
3. Cofactors are organic or inorganic substances that facilitate enzyme action.
II. Breaking Down Nutrients for Energy 12e TRA 15
The breakdown of glucose to energy starts with glycolysis to pyruvate. Pyruvate may be converted to lactic
A. Glucose
1. Glucose-to–pyruvate is called glycolysis or glucose splitting. 11e TRA 16
2. Pyruvate’s Options—Anaerobic or Aerobic
3. Pyruvate-to–Lactate 10e TRA 72
5. Acetyl CoA’s Options 10e TRA 74
a. Synthesize fats when the body has enough ATP.
b. Generate ATP when the cell is low in energy.
B. Glycerol and Fatty Acids
1. The conversion of glycerol to pyruvate is easy because they are both three-carbon compounds.
3. Fatty acids cannot be used to synthesize glucose. Glucose must be available to provide energy to the
C. Amino Acids 10e TRA 77
1. Amino acids can be converted energy.
D. Breaking Down Nutrients for Energy—In Summary
1. Glucose and fatty acids are primarily used for energy, amino acids to a lesser extent.
2. Glucose is made from all carbohydrates, most amino acids, and the glycerol portion of fat.
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E. The Final Steps of Catabolism
1. The TCA cycle contains a 4-carbon compound called oxaloacetate that has a critical role.
11e TRA 17
2. The Electron Transport Chain 10e TRA 81
3. The kCalories-per-Gram Secret Revealed 12e TRA 16
a. Fat provides 9 kcal/gram.
III. Energy Balance
When energy intake exceeds energy output, there is a gain in weight. Excess energy can come from protein, fat,
or carbohydrate. Fat is the most efficiently stored as fat.
A. Feasting—Excess Energy 10e TRA 83
1. Excess protein is converted to fat but this is inefficient and indirect. Its priority is other roles.
B. The transition from feasting to fasting draws on reserves. 10e TRA 84
C. Fasting—Inadequate Energy 10e TRA 85
1. Glucose is needed for the brain and nerve cells.
a. Ketones are produced when glucose is not available.
4. Ketosis causes a suppression of the appetite.
5. Hormones slow the metabolism.
6. Symptoms of Starvation:
a. Muscle wasting.
D. Low-Carbohydrate Diets
1. Result in changes in metabolism similar to what occurs during fasting.
IV. Highlight: Alcohol (ethyl alcohol, ethanol) and Nutrition IM CI 7.1, 7.2, 7.3
The metabolism of alcohol is handled differently in the body. Alcohol interferes with metabolism and impairs
health and nutrition. There are potential health benefits to consuming moderate amounts of alcohol.
A. Alcohol in Beverages
1. Beer, wine, and distilled liquor (hard liquor)
2. Alcohol behaves like a drug, therefore altering body functions.
B. Alcohol in the Body IM WS 7-2
1. Quickly absorbed.
C. Alcohol Arrives in the Liver 10e TRA 87
1. Accumulation of fatty acids.
D. Alcohol Disrupts the Liver 10e TRA 87
1. Development of a fatty liver is the first stage of liver deterioration.
2. Fibrosis is the second stage.
E. Alcohol Arrives in the Brain 11e TRA 18
1. Alcohol acts as a narcotic, anesthetizes pain
F. Alcohol and Malnutrition IM HN 7-1
1. Heavy drinkers may have inadequate food intake.
G. Alcohol’s Short-Term Effects
1. Accidents, fatalities, and breaking the law
H. Alcohol’s Long-Term Effects
1. Abuse during pregnancy.
3. Health Effects of Heavy Alcohol Consumption
a. Arthritis
b. Cancer
c. Fetal alcohol syndrome
I. Personal Strategies
1. Serve and consume nonalcoholic beverages.
3. Do not drive.
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Case Study
5
Steve Quintana is a 52-year-old Hispanic male with a family history of alcoholism. He is 6 feet 1 inch tall and
weighs 238 pounds, with much of his excess weight around his middle. He considers himself a social drinker
although he has been arrested for driving under the influence of alcohol twice in the past five years. He recently has
been diagnosed with diabetes and takes an oral medication to control his blood glucose. He also has high cholesterol
and has recently started on a lipid-lowering medication. Recent tests have revealed Steve has fatty liver, which he
feels is a result of his eating too much fat in his diet. He also reports having occasional low blood glucose
(hypoglycemia) and feeling shaky and dizzy.
1. From information in this chapter, explain to Steve how his alcohol intake may be contributing to fatty liver.
2. What might explain the low blood sugar reactions Steve has been having?
3. Describe how the MEOS system described in Highlight 7 might affect the efficacy of the medications Steve
takes.
4. What specific nutrient deficiencies is Steve at risk for due to excessive alcohol use?
5. Give Steve at least 3 health-related reasons to encourage him to seek help in abstaining from alcohol.
6. List at least 3 practical tips you would give to people who only drink alcohol occasionally and who want to stay
within current recommendations for health and safety.
Answer Key
1. Alcohol is broken down in the liver in preference over fatty acids, which then accumulate. Alcohol also
permanently changes the structure of liver cells, which impairs the liver’s ability to metabolize fats and can lead
to fatty liver.
Suggested Classroom Activities
To teach metabolism well—that is, to teach it so that students do not try to memorize fragments of it blindly but
become intrigued with it, feel comfortable with it, and really understand it—is a challenge. It helps when you are
enthused about the subject. It also helps to have your objectives clearly in mind, and not to be unrealistically
ambitious. Do you want students to memorize and spit back all of the TCA cycle intermediates with their structures,
or do you want them to be able to tell you in words what kinds of transformations can occur among amino acids,
fatty acids, and glucose? Offer as much as students are able to assimilate in the available time. It usually doesn’t pay
to get into the details of the TCA cycle at the beginning level; too few gain any real understanding.
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Classroom Activity 7-1: Chapter Opening Quiz
Objective: Introduction to chapter Class size: Any
Classroom Activity 7-2: Enhancing Understanding of Metabolism
6
Key concept: Metabolism basics Class size: Any
Ask students to consider a car having a manual transmission with only two gears: first and high. First gear is
beneficial for rapid acceleration. If you do not shift out of first gear, the car will no longer accelerate, and it will use
gasoline very inefficiently. You must shift into high gear to keep the car running efficiently at a higher speed.
Human beings obtain energy from two analogous processes: glycolysis and the TCA cycle. Anaerobic glycolysis
serves the need for quick energy to accomplish an intense activity for a short duration of time. For endurance
activities, additional energy must be obtained from the TCA cycle. Explain that the choice of activity determines the
proportion of fat and glucose burned during the activity.
Energy
Obtained
Measure of
Energy
Disadvantage
Car
First gear
Miles/gallon
Human beings
Glycolysis
ATP
Can only be used for a few seconds
to fuel source; better tuned engines
improves rate of oxygen delivery
Can only be used for a few seconds
Classroom Activity 7-3: Obtain Feedback Regarding Understanding of Metabolism
Objective: Review and clarification Class size: Any
Instructions: Chapter 7 is one of the most challenging chapters in the text. Asking for feedback regarding the
concepts that were grasped and others that were less understood can provide an excellent baseline regarding areas
Critical Thinking Questions
7
These questions will also be posted to the book’s website so that students can complete them online and e-mail their
answers to you.
1. Describe the following: catabolism, anabolism, coupled reactions, enzyme/coenzyme, photosynthesis, and
cofactor.
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Answer: Catabolism: This is the breakdown of energy-yielding compounds to provide energy for the body. For
instance, the body can break down fat or it can use its own muscle tissue to provide energy to the body in times
of starvation.
2. Discuss how the basic units of carbohydrate, protein, and lipid are utilized in energy pathways to produce
energy. What are the differences and similarities?
Answer: Carbohydrates, fats, and proteins all enter energy-producing pathways, but their fates do differ
slightly, depending on their role and chemical composition. For example, while carbohydrates and fats are
energy-yielding compounds, amino acids are really precursors to proteins and only a small percentage of their
dietary consumption will be used for energy.
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3. If there were no external sources of energy available to the body, what would it do to produce energy? Discuss.
Answer: If macronutrients are not available via ingested food, the body can rely on its stores of energy–yielding
compounds to survive, often for an extended period. Glycogenolysis in the liver breaks down glycogen stores,
4. In a state of starvation, several changes happen within our bodies. Talk about these metabolic changes and
discuss the importance of interventions such as IV glucose and tube feedings for hospital patients that are
severely sick and unable to eat.
Answer: In a state of starvation, the body continues to require energy to perform all of its functions. As noted
many times throughout your text thus far, the brain is only able to utilize glucose or ketones, as is the majority
of the nervous system. Even while an individual is asleep, the body continues to carry out thousands of
5. Using information regarding the pathways (biochemistry), discuss why dietary plans that only stress one or a
couple of food groups are unhealthy physiologically.
Answer: After reading this chapter, the student should be able to see the importance of not only all the
macronutrient groups but also the vitamins and minerals that assist as cofactors in many metabolic reactions.
All of the food groups work together to ensure that our bodies are properly nourished.
6. Many individuals enjoy a drink with friends or family during a special occasion and research does indicate that
drinking alcoholic beverages in moderation does have some positive health benefits (in particular wine).
However, alcohol consumption does have many negative consequences.
Discuss the differences between digestion and absorption of alcohol and that of other nutrients. Is alcohol a
nutrient? As a RD, what are the areas that you must be mindful of in counseling clients?
Answer: Alcohol is not a nutrient and thus not treated as a nutrient by the body. It can be very toxic to the
body; therefore, the body works quickly to excrete it. As such, alcohol is not digested but quickly absorbed in
the stomach and small intestine. If consumed with food, its absorption in the stomach will be disrupted. Alcohol
IM Worksheet Answer Key
Worksheet 7-1: Metabolism Exercises
Worksheet 7-2: Blood Alcohol Levels
1-3. Answers will vary based on the individual’s weight.
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4. Gender, tolerance of alcohol, other drugs used, amount of food present in the GI tract, certain medical
conditions, etc.
Worksheet 7-3: Anabolic or Catabolic?
Worksheet 7-4: Chapter 7 Crossword Puzzle
Worksheet 7-5: Carbohydrate Metabolism (Internet Exercise)
Canadian Information
8
7.1 Legal Drinking Age and Blood Alcohol Limit in Canada
The legal drinking age in most provinces and territories is 19 years, with the exception of Alberta, Manitoba, and
Quebec, where it is 18 years of age.
9
The permissible legal blood alcohol limit in the Criminal Code of Canada is
0.08 percent (80 milligrams of alcohol in 100 millilitres of blood). Canada lags behind international trends that
legislate a blood alcohol limit of 0.05 (50 milligrams of alcohol in 100 millilitres of blood).
10
7.2 Alcohol Use by Canadian University Students
The 2004 Canadian Campus Survey (CCS), funded by the Canadian Institutes of Heath Research, surveyed a
random sample of over 6200 students from 40 universities across Canada. Highlights from this survey showed
7.3 Alcohol Use Surveillance in Canada
In the past 20 years, national alcohol use by the general population has been collected in three surveys: the 1989
National Alcohol and Other Drugs Survey (NADS), the 1994 Canada’s Alcohol and Other Drugs Survey (CADS),
and the most recent 2004 Canadian Addiction Survey (CAS). In addition, Health Canada is currently conducting a
survey, the Canadian Alcohol and Drug Use Monitoring Survey (CADUMS), for the purposes of finding out how
many Canadians use alcohol, drugs and other substances, and how many Canadians are affected by the use of these
substances, even if they are not actually using them.
11
Overall, the rate of past-year drinking was higher in 1989 than
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Worksheet 7-1: Metabolism Exercises
Indicate whether each of the following reactions is anabolic or catabolic by circling the appropriate word:
Reaction Type of Reaction
1. Glucose + glucose → glycogen Anabolic Catabolic
2. C6H12O6 + 6H2O → 6CO2 + 6H2O Anabolic Catabolic
7. Electron transport chain Anabolic Catabolic
8. Oxidation reaction Anabolic Catabolic
9. Muscle tissue breakdown → release of amino acids Anabolic Catabolic
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Worksheet 7-2: Blood Alcohol Levels
Use the calculator to complete the table below based on your weight (choose the weight closest to yours from the
list). Select one type of drink from the list on the website, and use that same type of drink for each calculation. If
you drink, choose the beverage you like best or consume most often. Use 3 hours as the time period. Pay attention to
the description of your theoretical state (e.g., “possible impairment”) as well as your BAC.
Type of drink selected: _____________________________________________
Number of drinks
Blood alcohol concentration
1
2
3
4
5
6
7
8
Reflect on this information, and answer the following questions.
1. What did the website predict your state of alertness would be after 4 drinks? after 6? after 8?
2. After how many drinks did it predict your BAC would reach or exceed the legal limit for driving, 0.08%?
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Worksheet 7-3: Anabolic or Catabolic?
Metabolism explains how the cells in the body use nutrients to meet its needs. Cells may start with small,
simple compounds and use them as building blocks to form larger, more complex structures (anabolism).
These anabolic reactions involve doing work and so require energy. Alternatively, cells may break down
large compounds into smaller ones (catabolism). Catabolic reactions usually release energy. Determine
whether the following reactions are anabolic or catabolic.
Anabolic
Catabolic
1. A cracker becomes glucose.
2. Glucose becomes glycogen.
3. You consume more energy than your body expends.
4. Fasting.
5. A piece of ham becomes amino acids.
6. Amino acids become your muscles.
7. A cookie becomes fatty acids.
8. Fatty acids become body fat.
9. Fatty acids provide energy.
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Worksheet 7-4: Chapter 7 Crossword Puzzle
Across:
Down:
1. requiring oxygen
6. compounds that cells can use for energy
8. reactions requiring energy in which small molecules
are put together to build larger ones
2. small organic molecules that work with enzymes to
facilitate the enzymes’ activity
3. reactions in which large molecules are broken down
to smaller ones
1 2
3 4
5 6
7
8
9
10
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Worksheet 7-5: Carbohydrate Metabolism (Internet Exercise)
You may be asked to indicate from a drop-down menu the responses to several questions. Once you have answered
the initial set-up questions, you will be automatically directed to the video.
Do not close the window until you have finished answering the questions.
1. Anabolism releases energy as new compounds are built.
a. True
b. False
2. Enzymes are protein-based in nature.
3. Enzymes are non-specific for substrate and can be used interchangeably in chemical reactions.
4. In order for metabolism reactions to occur the body has to maintain a stable pH environment and core
5. The major production of energy within the cell occurs in the endoplasmic reticulum.
6. The combination of several glucose molecules to form glycogen is an example of an anabolic reaction.
7. The ability to store glycogen in the liver is critical for use in fueling the body when activity is limited.
a. True
b. False
8. The only end products of carbohydrate metabolism are energy in the form of ATP and water.
9. The process of glycolysis requires oxygen.
10. Excess glucose can be converted to fatty acids.
a. True
b. False