An Energy Shuttle for Biosynthesis Key Terms: ATP, NADH, FADH

Chapter Outline I. Energy: Fuel for Work. *Energy is necessary to do any kind of work. The body converts chemical energy from food sources—carbohydrates, proteins, and fats—into a form usable by cells. A. Transferring food energy to cellular energy (Figure 8.2) B. What is metabolism (Figure 8.3)? *Anabolic reactions (anabolism) build compounds. These reactions require energy. Catabolic reactions (catabolism) break compounds into smaller units. These reactions produce the energy. C. The cell is the metabolic processing center (Figure 8.4) Key terms: metabolism chemical energy, photosynthesis, metabolite, metabolic pathway, catabolism, anabolism, cell, nucleus, cytoplasm, cytosol, organelle, mitochondria, cofactor, coenzyme

II. Who Are the Key Energy Players? A. ATP: The Body’s Energy Currency (Figure 8.5). *Adenosine triphosphate (ATP) is the energy currency of the body.

B. NADH and FADH2: The Body’s Energy Shuttles. *The body’s energy shuttles

NADH, FADH2, and NADPH are important carriers of hydrogen and high-energy

electrons. NADH and FADH2 are used in making ATP, while NADPH is used in biosynthetic reactions. C. NADPH: An Energy Shuttle for Biosynthesis

Key terms: ATP, NADH, FADH2, NADPH, biosynthesis, ADP, pyrophosphate, AMP, GTP, NAD, hydrogen ion, FAD

III. Breakdown and Release of Energy. *Cells extract energy from carbohydrate via four main pathways: glycolysis, pyruvate into acetyl CoA, the citric acid cycle, and the electron transport chain. A. Extracting Energy from Carbohydrate (Table 8.1). *The citric acid cycle and electron transport chain require oxygen. Glycolysis does not. 1. Glycolysis 2. Conversion of pyruvate to acetyl CoA 3. Citric acid cycle 4. Electron transport chain. The electron transport chain produces more ATP than the other catabolic pathways. 5. End products of glucose catabolism B. Extracting energy from fat. *To extract energy from fat, first triglycerides are separated into glycerol and fatty acids. Next, beta-oxidation breaks down the fatty

acids to yield acetyl CoA, NADH, and FADH2. The acetyl CoA enters the citric acid

cycle, producing more NADH and FADH2. The NADH and FADH2 deliver their high-energy electrons to the electron transport chain to make ATP. 1. Carnitine shuttle 2. Beta-oxidation (Figure 8.14)

3. The citric acid cycle and electron transport chain complete fatty acid breakdown (Figure 8.15) C. Fat burns in a flame of carbohydrate D. Extracting energy from protein 1. Carbon skeletons enter pathways at different points. *To extract energy from amino acids, first it is deaminated (the amino acid is removed). Depending on the structure of the remaining carbon skeleton, it enters the catabolic pathways as pyruvate, acetyl CoA, or a citric acid cycle intermediate. The citric acid cycle and the electron transport chain complete the production of ATP. 2. End products of amino acid catabolism. *The liver converts the nitrogen portion of amino acids to urea, which the kidney excretes. Key terms: glycolysis, anaerobic, pyruvate, aerobic, acetyl CoA, coenzyme A, lactate, citric acid cycle, oxaloacetate, Krebs cycle, tricarboxylic acid cycle, electron transport chain, mitochondrial membrane, oxidative phosphorylation, carnitine, beta-oxidation, deamination

IV. Alcohol Metabolism A. Metabolizing small amounts of alcohol (Figure 8.18) B. Metabolizing large amounts of alcohol (Figure 8.19) Key terms: alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), microsomal ethanol-oxidizing system (MEOS)

V. Biosynthesis and Storage (Figure 8.20). *Tissues differ in their preferred source of fuel. The brain, nervous system, and red blood cells rely primarily on glucose, while other tissues use a mix of glucose, fatty acids, and ketone bodies as fuel sources. A. Making carbohydrate (glucose). *When carbohydrate is available, glucose can be stored as glycogen in liver and muscle tissue. 1. Gluconeogenesis: pathways to glucose (Figure 8.21). *Glucose can be produced from the noncarbohydrate precursors glycerol and some (glucogenic) amino acids, but not from fatty acids. 2. Storage: Glucose to Glycogen B. Making fat (fatty acids) 1. Lipogenesis: pathways to fatty acids 2. Storage: dietary energy to stored triglyceride (Table 8.3) C. Making ketone bodies (Figure 7.20) 1. Ketogenesis: pathways to ketone bodies D. Making protein (amino acids) 1. Biosynthesis: making amino acids Key terms: gluconeogenesis, glycogenesis, glycogenolysis, lipogenesis, ketones, ketogenesis, ketoacidosis, transamination

V. Regulation of Metabolism. *The hormone insulin regulates metabolism by favoring anabolic pathways. It promotes the uptake of glucose by cells, thus removing it from the bloodstream. Glucagon, cortisol, and epinephrine stimulate catabolic pathways. These hormones promote the breakdown of glycogen to glucose and of amino acids to make

glucose via gluconeogenesis. The breakdown of liver glycogen increases the amount of glucose in the blood. A. Hormones of metabolism B. Special states 1. Feasting (Figure 8.24). *Feasting, or overconsumption of energy, leads to glycogen and triglyceride storage. a. The return to normal 2. Fasting (Figure 8.25). *Fasting, or underconsumption of energy, leads to mobilization of liver glycogen and stored triglycerides. Starvation, the state of prolonged fasting, leads to protein breakdown as well and can be fatal. a. Survival priorities and potential energy sources b. The prolonged fast: in the beginning c. The first few days (Figure 8.26) d. The early weeks e. Several weeks of fasting f. The end is near

Classroom Activities ACTIVITY 1: TRIVIA See Activity 1 in Chapter 1 for an explanation on implementing trivia exercises into your classroom.

TRIVIA QUESTIONS

Name two of the forms of energy in biological systems. ANSWER: heat, mechanical, electrical, and chemical

TRIVIA: What is the term for all chemical reactions within organisms that enable them to maintain life? ANSWER: metabolism

TRIVIA: What are the two main categories of metabolism? ANSWER: catabolism and anabolism

TRIVIA: Photosynthesis involves green plants using radiant energy from the sun to produce this macronutrient. ANSWER: carbohydrate

TRIVIA: Name one of the two parts of the basic animal cell. ANSWER: cell nucleus and cytoplasm

TRIVIA: What is the name for the powerhouses of cells? ANSWER: mitochondria

TRIVIA: What is the fundamental energy molecule used to power cellular functions? ANSWER: adenosine triphosphate (ATP)

TRIVIA: How long is the typical lifetime of an ATP molecule? ANSWER: less than 1 minute

TRIVIA: Name one out of three pathways cells extract energy from carbohydrates. ANSWER: glycolysis, the citric acid cycle, and the electron transport chain

TRIVIA: Triglycerides are broken down into what two components so that energy can be extracted from fat? ANSWER: glycerol and fatty acids

TRIVIA: What element does the citric acid cycle and electron transport chain require that glycolysis does not? ANSWER: oxygen

TRIVIA: What is the main storage form of glucose? ANSWER: glycogen

TRIVIA: What is the nitrogen portion of amino acids converted to? ANSWER: urea

TRIVIA: What organ excretes urea? ANSWER: kidneys

TRIVIA: What is the preferred energy source for the brain? ANSWER: carbohydrates

TRIVIA: True or False? Glucose can be produced from fatty acids. ANSWER: false

TRIVIA: What hormone promotes the uptake of glucose by cells, thus removing glucose from the bloodstream? ANSWER: insulin

TRIVIA: Name one out of the three hormones that promote the breakdown of glycogen to glucose. ANSWER: glucagon, cortisol, and epinephrine

TRIVIA: What is the term for the breakdown of amino acids to make glucose? ANSWER: gluconeogenesis

TRIVIA: True or False? Fasting causes the body to use energy more efficiently. ANSWER: true

ACTIVITY 2: PROCESSES FOR ENERGY PRODUCTION This activity can be used to help students understand how energy is derived from macro- nutrients and plants. Students should be asked to put the following steps under each process in the correct order that they happen in energy production.

Process—Transferring Food Energy to Cellular Energy a. Transfer of energy to a form that cells can use b. Digestion, absorption, and transportation or nutrients c. Break down of the many small molecules to a few key metabolites ANSWERS: b, c, a

Process—Photosynthesis a. Plants store glucose as starch and release oxygen into the atmosphere. b. Carbon dioxide from the air combines with water from the earth to form a carbohydrate (glucose) and oxygen. c. In the glucose molecules, the chemical bonds between the carbon and hydrogen atoms hold the energy from the sun. ANSWERS: b, a, c

Process—Extracting Energy from Fat

a. NADH and FADH2 deliver their high-energy electrons to the electron transport chain to make ATP.

b. The acetyl CoA enters the citric acid cycle, producing more NADH and FADH.2 c. Beta-oxidation breaks down the fatty acids to yield acetyl CoA, NADH, and FADH2. d. Triglycerides are separated into glycerol and fatty acids. ANSWERS: d, c, b, a

Process—Extracting Energy from Amino Acids a. The amino group is removed (deaminated). b. Depending on the structure of the remaining carbon skeleton, the amino group enters the catabolic pathways as pyruvate, acetyl CoA, or a citric acid cycle intermediate. c. Completion of the production of ATP. d. The citric acid cycle and the electron transport chain become involved in producing ATP. ANSWERS: a, b, d, c