CH-7-9 How Cells Harvest Energy – Understanding Biology : Chapter Notes

This Document Contains Chapters 7 to 9 CHAPTER 7: HOW CELLS HARVEST ENERGY WHERE DOES IT ALL FIT IN? Chapter 7 builds upon the cell anatomy coverage of Chapter 4 and information about cellular energy in Chapter 6. It provides students with details of cellular metabolism using cell respiration as a model pathway. All of the principles covered in Chapters 2 through 6 culminated in this chapter and should be gently reviewed as concepts in this chapter are covered. The information in Chapter 7 is crucial for students to understand other concepts that integrate cell function to homeostasis and development. SYNOPSIS Biological endergonic reactions do not occur spontaneously and are generally coupled with reactions that split energy-carrying molecules like ATP. ATP is not a long-term energy storage molecule, it is made only when needed. It is an extremely valuable molecule because it is used to do most of the work in a cell and is used to drive endergonic reactions. Cells generate ATP through two different processes, substrate level phosphorylation and chemiosmosis. The substrate level phosphorylation produces ATP from ADP and phosphate by association with an exergonic reaction and is the more ancient process. Chemiosmosis occurs when protons pumped out through specific transmembrane channels re-enter through other channels coupled to ATP synthesis. Most biological ATP is produced in this manner. Glycolysis occurs in the cytoplasm of a cell and is catalyzed by enzymes not associated with any membranes or organelles. Glucose is converted to two glyceraldehyde-3-phosphate (G3P) molecules in a reaction that costs two ATP molecules. G3P is then converted to pyruvate and produces four ATPs via substrate level phosphorylation, a process that occurs with or without oxygen. In addition, a pair of electrons and one proton are removed from G3P reducing the coenzyme NAD+ to NADH. The net energy yield at this point is two ATPs per glucose. Glycolysis continues as long as there is a fresh supply of glucose and there is sufficient NAD+. It is advantageous for a cell to do something with its NADH other than allowing it to build up because its supply of NAD+ is generally limited. NADH returns to NAD+ through aerobic respiration. The process of aerobic respiration includes the oxidation of pyruvate to acetyl-CoA and the Krebs cycle. Pyruvate is oxidized to a two-carbon molecule, acetyl-CoA, one NAD+ is reduced to NADH and one molecule of CO2 is given off. This reaction occurs within the mitochondria of eukaryotes or on special membranes in a few bacteria. The Krebs cycle is a complex set of reactions in which a four-carbon molecule is added to the acetyl-CoA from pyruvate oxidation. During the cycle, two molecules of CO2 are given off and three NADH, one FADH2, and one ATP are produced. These quantities are, of course, for a single molecule of pyruvate. The degradation of a whole molecule of glucose produces twice the quantity of each substance. Oxidative respiration in itself produces no more ATP than glycolysis, but it becomes highly efficient only when it is coupled to the fourth stage, the chemiosmotic generation of ATP via an electron transport chain. This process occurs on the inner mitochondrial membrane, requires oxygen as a final electron acceptor, and therefore occurs only in aerobic organisms. In theory, each NADH from the oxidative respiration (a total of eight per glucose) activates three pumps and produces three ATPs (a total of 24). Each FADH2 from the Krebs cycle (two per glucose) activates two pumps and generates two ATPs (a total of four). The cell uses one ATP to get the NADH from glycolysis (a total of two) into the mitochondrion, thus the net value of each is only two ATPs (a total of four). Overall, glycolysis plus complete oxidative respiration produces 32 ATPs via chemiosmosis and four ATPs by substrate level phosphorylation. In actuality, the mitochondrial membrane is leaky, and only 2.5 ATPs are produced per NADH and 1.5 per FADH2. Thus, on average, closer to 30 ATP are produced by chemiosmosis in the electron transport chain. Proteins and fats are also metabolized. Proteins provide the same efficiency as glucose as constituent amino acids are converted to participants in the Krebs cycle. Fats are metabolized via -oxidation during which two ¬carbon chunks are converted to acetyl-CoA, NADH, and FADH2 molecules. A six carbon fatty acid molecule produces 36 actual ATP compared to 30 actual from a six carbon sugar. The NADH produced in glycolysis also returns to NAD+ through various anaerobic fermentations. A carbohydrate serves as the final electron acceptor in most fermentations. Products of familiar eukaryotic fermentations include ethyl alcohol and carbon dioxide by yeast and lactic acid by overworked muscle cells. The stages of cellular respiration have evolved over time through 6 major events, each building on what had come before. LEARNING OUTCOMES 7.1 Cells Harvest Energy from Organic Compounds by Oxidation 1. Distinguish between oxidation and reduction reactions. 2. Describe the structure of NAD+ and explain its role in energy metabolism. 3. Contrast substrate-level phosphorylation with oxidative phosphorylation. 7.2 Glycolysis Splits Glucose and Yields a Small Amount of Energy 1. Explain the process of glycolysis, including its energy yield. 2. Distinguish between aerobic respiration and fermentation. 7.3 The Krebs Cycle Is the Oxidative Core of Cellular Respiration 1. Explain how the oxidation of pyruvates links glycolysis with the rest of respiration. 2. Explain the fate of the electrons produced as products of the Krebs Cycle. 3. Describe the nine reactions of the Krebs cycle, stating where in the cell they take place. 7.4 Electrons Harvested by Oxidation Pass Along an Electron Transport Chain 1. Describe the journey of an electron through the electron transport chain, identifying its final destination. 2. Describe the location, structure, and chemiosmotic function of ATP synthase. 7.5 The Energy Yield of Aerobic Respiration Far Exceeds That of Glycolysis 1. Calculate the number of ATP produced by a cell via aerobic respiration. 2. Explain how our understanding of the P/O ratio has changed over time. 7.6 Aerobic Respiration Is Regulated by Feedback Inhibition 1. Identify the two key points at which cells can control the cellular respiration process. 7.7 Oxidation Can Occur Without O2 1. Describe two ways in which prokaryotes carry out respiration in the complete absence of oxygen. 2. Define fermentation, and distinguish between ethanol and lactic acid fermentations. 7.8 Carbohydrates Are Not the Only Energy Source of Heterotrophs 1. Explain how cells extract energy from proteins. 2. Calculate how many ATP can be produced by a fatty acid of a given length. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 7 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe respiration is the same as breathing • Students believe food is anything that goes into the organism including minerals, water, carbon dioxide • Carbon dioxide is formed from oxygen during cellular respiration • Water is not a product of cellular respiration • Oxygen burns the food molecules during cellular respiration • Glycolysis is the same as fermentation • Cellular respiration always breaks down glucose completely and always makes 36 ATP per molecule • All of the energy produced by mitochondria is converted to ATP • The Krebs cycle takes place in the cytoplasm • Each glucose molecule undergoes one Krebs Cycle and ETC event • ATP gives energy to a cell • ATP is produced in the body and not in the cell • Only carbohydrates are involved in ATP production • Glucose is the only molecule that fuels ATP • ATP production increases with calories taken in the diet • Lipids are solely consumed during weight loss • Enzymes are so highly selective that they only bind to one type of substrate • Enzymes cannot bind to products of their reaction • Dietary calories (kilocalories) are the same as the standard calorie unit INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Another analogy to help explain the value of controlled pathways is jumping off a skyscraper. Without controlled pathways, i.e., stairs, you go splat! With a controlled pathway, you may be a little out of breath and have tired legs, but you get down in one piece. Even if you stumble or fall down a few, at least you are not dead! Also, unless you are Superman, you’re not going to be able to leap tall buildings in a single bound and do the pathway in reverse. It is possible, albeit exhausting, to climb the stairs. There must be a clear differentiation between the generation of ATP via substrate-level phosphorylation and chemiosmosis. The former occurs directly in the cytoplasm. The latter requires a membrane bound proton pump. In eukaryotes, chemiosmosis is associated with the mitochondria, the electron transport chain and oxygen as the final electron acceptor. If any of these are not present, NADH will not be converted to ATP. It is important to stress where each of the stages of cellular respiration occur, how ATP from each is generated, and whether it relies on NAD+ or FAD+ as electron carriers. Figures 7.6, 7.11, and 7.14 are especially valuable in presenting “the big picture.” Remind students that the products of the Krebs cycle must be doubled for each molecule of glucose degraded. However, the products of glycolysis are not doubled. Also remind them to be careful in converting NADH to ATP. Those produced in the cytoplasm (through glycolysis) are worth only 2 theoretical (or 1.5 actual) ATP, those produced in the mitochondria are worth 3 theoretical (or 2.5 actual) ATPs. You may find it valuable to color-code or specially label the energy products of each stage as you go through. Instruct the students to do the same in their class notes. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 7. Application • Have students explain why a person does not need carbohydrates as a source of ATP. • Have students describe a possible mechanism for the observation that high levels of carbon dioxide cause yeast to switch from aerobic to anaerobic respiration. • Ask students to explain why long-term high protein diets can result in kidney damage. Analysis • Ask students to explain the activity of glycolysis in organisms that obtain energy from diets consisting of lipids and proteins. • Ask students to explain the activities of cellular respiration if oxygen uptake is block by carbon monoxide poisoning. • Ask students to hypothesize why it is normal for ATP to inhibit the Krebs cycle. Synthesis • Ask students predict the commercial applications of a technique that causes mitochondria to transport electrons to a metal ion instead of oxygen. • Have students explain agricultural researchers have evidence that almost all of the metabolic rate of offspring comes from the female parent. • Ask students to explain the changes in how cellular respiration operates in diabetics who are not able to shuttle glucose rapidly into cells. Evaluation • Ask students to evaluate the benefits an athlete may derive by resting and eating lots of carbohydrates a day before a high performance athletic event. • Ask students to refute the claim that consuming sports drinks containing phosphorus increases the body’s ability to produce ATP. • Have the students evaluate the claim the diets high in fructose are just as effective at providing energy for the body as high glucose diets. VISUAL RESOURCES Prepare bunches of colored cards, a different color to represent ADP, ATP, NAD+, NADH, FAD+, and FADH2. This currency can be distributed as you present each stage of cellular respiration. For example, a bacteria cell ready for fermentation starts with two ATPs and two NAD+. Take the two ATPs to start glycolysis. Then take the two NAD+ and give out two NADH and four ATPs. When you try to run through glycolysis again, there are no NAD+. After alcoholic fermentation occurs, trade the two NADH for two NAD+ and do another glycolysis reaction. Aerobic respiration can be done in a similar manner. IN-CLASS CONCEPTUAL DEMONSTRATIONS Name That Molecule Game Introduction A mock game show is a fun and effective way to review the pathways of cellular respiration. Encourage the students to come up with questions that would test the knowledge of their classmates Materials • Large index cards • Thick black marker • Student volunteers Procedure & Inquiry 1. Label the index cards to represent one concept of cellular respiration. Possible labels are: a. Glucose b. Fructose-6-phosphate c. ATP synthase d. Mitochondrial inner membrane e. Pyruvate 2. Announce to the class that a student will be called down to class to receive an index card containing the name of a molecule or structure associated with cellular respiration. The label cannot be seen by the class. 3. Then tell the class that they have to figure out the molecule or structure based on a statement of fact made by the student holding the card. 4. Ask a student to come down to the room and hand them a labeled index card so that the card is not facing the class 5. Tell the student that they must give the class some fact about the molecule or structure without giving away its name. 6. The class must guess the answer based on the student’s facts. Inaccurate hints should be brought up and corrected by other students. 7. A correct answer results in another student coming down to pick up a different labeled card. LABORATORY IDEAS A. Specificity of Glycolysis Have students perform a simple experiment in which students investigate the ability of yeast to metabolize different sugars and sweeteners. a. Tell the class that they will be using yeast as a model for measuring the ability for various sugars and sweeteners to be used in glycolysis. b. Students should be able to make a setup that that evaluates metabolic waste production. They can come up with a way to detect carbon dioxide by looking at bubbles forming in solution or by measuring the drop of pH in the solution due to the buildup of carbonic acid. c. Provide students with the following materials: i. Fast rising baker’s yeast ii. Test tube rack iii. 6 test tubes iv. pH paper v. Distilled water (negative control) vi. 0.5% d-glucose solution (positive control) vii. 0.5% l-glucose solution viii. 0.5% fructose solution ix. 0.5% saccharine solution x. 0.5% Splenda solution d. Instruct the students to design an experiment to test if yeast are able to metabolize particular sugars or sweeteners. e. Tell them that they must first determine which sugar in the samples provided will be the positive control and how they should compare it to a negative or “no results” control. f. Have the students explain why a particular sugar or sweetener worked or did not work as a source of material for cellular respiration. LABORATORY IDEAS Effect of Temperature on Cellular Respiration Have students perform a simple experiment in which students investigate the relationship between temperature and rate of cellular respiration. a. Tell the class that they will be using yeast as a model investigating the relationship between temperature and cellular respiration. b. Students should be able to make a setup that that evaluates carbon dioxide as an indicator of cellular respiration. They can come up with a way to detect carbon dioxide by looking at bubbles forming in solution or by measuring the drop of pH in the solution due to the buildup of carbonic acid. c. Provide students with the following materials: i. Fast rising baker’s yeast ii. 0.5% glucose solution iii. Test tube rack iv. Test tubes v. Thermometer vi. pH paper vii. Hot plate viii. Ice bath g. Instruct the students to design an experiment to test the relationship between temperature and cellular respiration. h. Tell them that they must first determine what would be an appropriate temperature range to test. i. Ask the students to see if their estimates match the literature about the rate of change of enzymatic reaction in relationship to temperature. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. Students who have successfully mastered the content of Chapter 7 can apply their knowledge for service learning activities in the following ways: 1. Have students talk to youth sports groups about the risks of high-protein diets. 2. Have students design prepare an electronic presentation for school teachers about the pathways of cellular respiration. 3. Have students tutor middle school or high school biology students studying cell metabolism. 4. Have students give demonstrations to boy scouts or girl scouts using yeast a model for understanding commercial applications of cellular respiration. ETYMOLOGY OF KEY TERMS auto- self; same; spontaneous (from the Greek auto- self) chondri- grain or grainy (from the Greek chondros- grain or corn) ferment to decompose (from the Latin fermentum- decompose) glyco- of, or relating to, sugar (from the Greek glykys- sweet) lys (lysis) dissolution; breaking (from the Greek lysis- dissolution) mito- thread (from the Greek mitos- a thread) CHAPTER 8: PHOTOSYNTHESIS WHERE DOES IT ALL FIT IN? Chapter 8 applies the information covered in Chapters 3, 5 and 7 in its coverage of photosynthesis. It provides students the principles of thermodynamics and metabolism needed to understand photosynthesis. It is important to briefly review the material in Chapter 3 and 4 before proceeding with Chapter 8. The information in Chapter 8 is crucial for students to understand the principles of evolution and ecosystems covered later in the book. SYNOPSIS Eukaryotic chloroplasts are composed of stacks of thylakoid disks called grana located within the stroma, a fluid matrix. The photosynthetic pigments are bound to the thylakoid membrane which pumps protons from the stroma to the interior. ATP molecules are generated as the protons diffuse back out to the stroma. The enzymes of the Calvin cycle are in the stroma. Photosynthesis is composed of two very different processes: the light reactions and the Calvin cycle. The light reactions occur in eukaryotic chloroplasts on specific photosynthetic membranes of bacteria. The pigment captures a photon of light and excites one of its electrons. The excited electron shuttles through various carrier molecules to a final acceptor and chemiosmotic ally generates ATP and NADPH. The Calvin cycle fixes carbon by using the products of the light reactions to chemically reduce carbon dioxide into organic molecules. Early research in plant physiology showed that plants did not derive major nutrients from the soil to support their growth, but that the sun’s energy and carbon dioxide were required. Light energy exists in the form of packets called photons. Photons of short wavelength light are more energetic than photons of long wavelength light. The energy in these photons is captured by carotenoid or chlorophyll pigments. The former absorb photons with a broad range of energy and are not highly efficient, while the latter absorb a narrow range of photons very efficiently. Most photosynthetic organisms use chlorophylls as their light gathering pigment. Early photosynthetic bacteria exhibited cyclic photophosphorylation, a process that only produces ATP and does not provide for biosynthesis. The bacterial reaction center channels its light energy to P870, which then passes to a primary electron acceptor. The electron returns to the pigment through an electron transport chain. This drives a proton pump and produces ATP through chemiosmosis. Other bacteria improved on this photosystem, utilizing chlorophyll a to absorb the more energetic photons associated with shorter wavelengths of light. The P680 pigment of photosystem II became the first stage of a two stage photosystem while P700 remained as the pigment of photosystem I. The excited electron of photosystem II drives a proton pump and chemiosmotic ally generates ATP. The electron then passes on to photosystem I where it absorbs another photon of energy. This electron is channeled to the primary electron acceptor where it generates reducing power by reducing NADP+ to NADPH. The electron removed from photosystem II is replaced by an electron obtained from the splitting of a molecule of water. Oxygen is a byproduct of this reaction, called noncyclic photophosphorylation. Carbon fixation is similar to glycolysis, but runs in reverse. The Calvin cycle uses ATP energy and NADPH reducing power to make organic molecules from carbon dioxide. Carbon dioxide attaches to the five-carbon molecule ribulose bisphosphate (RuBP) and is then split into two molecules of three-carbon phosphoglycerate (PGA) by an enzyme called rubisco. Some of these molecules are used to reconstitute RuBP; others are assembled into sugars via glyceraldehyde-3-phosphate (G3P). Six turns of the cycle are needed to form glucose. Plants that exhibit C3 photosynthesis lose much of their fixed carbon when RuBP carboxylase interferes with the Calvin cycle, a process called photorespiration. C4 plants expend ATP to concentrate carbon dioxide in the cells that carry out the Calvin cycle. This high concentration of carbon dioxide prevents RuBP carboxylase from binding oxygen and thus reduces photorespiration. The loss of ATP greatly outweighs the potential loss of fixed carbon. Many succulent plants reduce photorespiration by closing their stomata and thus decrease the amount of carbon dioxide present during the day. These plants are called CAM plants; they use both C3 and C4 pathways within the same cells. C4 plants use both pathways, but do each in a different cell. LEARNING OUTCOMES 8.1 Photosynthesis Uses Sunlight to Power the Synthesis of Organic Molecules 1. Write the balanced equation for photosynthesis. 2. Compare the structure of a chloroplast with the structure of a mitochondrion. 8.2 Experiments Revealed that Photosynthesis Is a Chemical Processes 1. Demonstrate that plant mass is derived primarily from the air and not the soil. 2. Demonstrate that a key portion of photosynthesis does not use light. 3. Explain how photosynthesis generates O2. 4. Demonstrate that electrons from water are used to reduce NADP+. 8.3 Pigments Capture Energy from Sunlight 1. Relate a photon’s energy to its wavelength. 2. Relate the chlorophyll absorption spectra to the photosynthetic action spectrum. 3. Explain the role of accessory pigments. 8.4 Photosynthetic Pigments Are Organized into Photosystems 1. Demonstrate the existence of photosystems in plant leaves. 2. Differentiate between reaction center chlorophyll and other chlorophyll molecules in a photosystem. 8.5 Energy from Sunlight Is Used to Produce a Proton Gradient 1. Describe the four stages of the light-dependent reactions. 2. Compare chloroplast photosystems with bacterial photosystems. 3. Differentiate between the functions of photosystem I and photosystem II. 4. Describe how a proton gradient acts as the energy source for ATP synthesis. 8.6 Using ATP and NADPH from the Light Reactions, CO2 Is Incorporated into Organic Molecules 1. Diagram the action of rubisco in the Calvin cycle. 2. Describe how the Calvin cycle can produce a molecule of glucose. 8.7 Photorespiration Short-Circuits Photosynhesis 1. Compare and contrast C3 plants with C4 and CAM plants. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 8 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe photosynthesis is the opposite of respiration • Students believe that photosynthesis is carried out in place of photosynthesis • Students believe plants lack mitochondria • Students believe food is anything that goes into the organism including minerals, water, carbon dioxide • Carbon dioxide is converted to oxygen during photosynthesis • Students believe that all water taken in plants is for turgor and evapotranspiration • Photosynthesis requires a green plant • Photosynthesis is a simple process make up of only two pathways • The dark reactions take place at night • Plants get most of their food from the soil • Plants are green because they absorb only green light • Carnivorous plants get their “food” from insects • Cellular respiration in plants only occurs at night • Photosynthesis only occurs in leaves • Plant mass comes from water and minerals • Glucose is the only produce of photosynthesis INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Many texts simply present photosynthesis straight through. Here it is presented from an evolutionary as well as biochemical viewpoint. PS I with P700 was “invented” first and makes enough ATP for growth and reproduction, but doesn’t produce NADPH or fix carbon. PS II with P680 was “invented” next and added to the front of PS I. In cyanobacteria, algae, and plants, PS II occurs first and is followed by PS I. (This evolution is different from cellular respiration where the new process was added to the end of the original one.) PS II produces ATP while PS I now generates NADPH, reducing power used to fix carbon in the Calvin cycle. You may want to ask why it wouldn’t be simpler to just add PS II to the end of PS I so that PS I could still make ATP with PS II generating NADPH. (ANSWER: The electron from P700 isn’t energetic enough to split water, the one from P680 has more energy. Remember that photon energy is inversely proportional to the wavelength.) Stress why water is split, why oxygen is produced, and that two photons of different energy are needed for PS I/PS II photosynthesis. It is important that the students also remember that the Calvin cycle (aka the dark reaction) does not ONLY occur in the dark. It also occurs in the light, but does not require light to occur as do the light reactions. Many students may confuse photorespiration with cellular respiration, but they are two entirely different processes. Although they both produce CO2, photorespiration is a damaging reaction because it does not produce ATP. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 8. Application • Have students describe the fate of a molecule of radioactive carbon dioxide taken up by a tree. • Have students explain why farmers at one time removed trees that grew near their fields of crops. • Ask students explain how the nutritional content could be affected by not providing crops with nitrogen. Analysis • Ask students to explain the value of using tree planting programs as a means of curbing global climate change. • Ask students to explain why specific organs in certain plants produce chemicals that inhibit starch digestion. • Ask come with a way that plants can be used to reduce urban flooding. Synthesis • Ask students come up with a way that plants can be used as means of producing electricity for running households. • Have students develop a rationale for encouraging the growing of corn in warmer climates and cotton in cooler regions of the North America. • Ask students to describe the conditions needed to keep alive a plant that completely lacks chloroplasts. Evaluation • Ask students to evaluate the benefits and limitations of using aquatic plants to remove pollutants from water. • Ask students to evaluate the practice of removing plants from hospital rooms. • Have the students evaluate a city regulation requiring all large buildings to have plants in office buildings as a way of improving the air quality. VISUAL RESOURCES Chloroplasts reradiate light with a longer wavelength than the light that they are initially illuminated. A beaker of chloroplasts illuminated with normal light will reradiate at invisible infrared wavelengths. One that is illuminated with higher energy ultraviolet light will reradiate in the visible red range. IN-CLASS CONCEPTUAL DEMONSTRATIONS Guess the Function of the Plant Pigments Introduction Many students believe that photosynthetic pigments in leaves are solely for purpose of photosynthesis. This demonstration guides students to investigate the roles of other pigments involved in plant survival. The demonstration should be prepared before class. Chromatograms can be stored several months chilled in a dark container. Materials • Chromatography paper or thick filter paper • Knife and cutting board • Mortar and pestle • Capillary pipettes • Short wave ultraviolet light • Acetone • Spinach • Green tea leaves • Red cabbage • Mobile phase solution composed of 100 ml of petrol ether, 11 ml of acetone, 5 drops of distilled water, and 5 drops of acetic acid • Three large glass jars with lids as chromatography chambers • Short wave ultraviolet light • Video came with hook-up to LCD projector or other projection device Procedure and Inquiry 1. Grind up the spinach, red cabbage, and green tea leaves separately in acetone 2. Collect the solution when it is rich in color 3. Set up three chromatography setups using the mobile phase formulation 4. Transfer the solutions to separate chromatography setups using the capillary pipettes and three large jars 5. Run the setups to get the maximum separation of pigments 6. Dry the chromatogram and store in a cool dark place 7. Project the spinach chromatograms to the class and have students identify the photosynthetic pigments 8. Then compare the red cabbage and tea chromatograms to the spinach 9. Ask the students to identify the differences and hypothesize the roles of the pigments not found in the spinach (lead them into a discussion about leave pigments that collect different wavelengths of light and that protect the plant from too much sunlight) 10. Then show all three of the chromatograms exposed to ultraviolet light 11. Ask the student to describe what they see (they should see a bluish glow from the tea where there was no visible spot) 12. Have them speculate the function of UV fluorescent pigments (reduces UV damage to plants) 13. Then inquire to any potential commercial or medical purposes for UV fluorescent pigments LABORATORY IDEAS A. Fueling Photosynthesis Have students perform a simple experiment in which students use photosynthesis to hypothesize the chemical composition of an unknown substance added to plant cells. a. Tell the class that they will be using their knowledge of photosynthesis to identify the probable nature of an unknown chemical. b. They will be adding the chemical to an aquatic plant and use the plant’s reaction to the chemical as an indicator of the chemical’s identity. c. Provide students with the following materials: a. Microscope b. Microscope slides and cover slip c. Fresh elodea exposed to bright light for at least 8 hours d. Sodium bicarbonate in bottles labeled “Unknown” e. Small scoop for transferring sodium bicarbonate d. Have students carry out the following procedure: a. Tell students to make a wet mount of elodea leaf b. Have them observe the edges of elodea leaves c. Ask to look for bubble formation d. Ask them to explain the nature of the bubbles (oxygen) e. Then ask the students to add the unknown powder f. Have them watch the elodea cells to see any changes g. They should observe an increase in bubble production h. Have the class explain why oxygen production increased i. They should then hypothesize that they added carbon dioxide j. Then have the students investigate chemicals that produce carbon dioxide when dissolved in water LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. Students who have successfully mastered the content of Chapter 8 can apply their knowledge for service learning activities in the following ways: 1. Have students do a presentation about the environmental benefits of keeping their neighborhoods “green”. 2. Have students design prepare an electronic presentation for school teachers about the pathways of photosynthesis. 3. Have students tutor middle school or high school biology students studying photosynthesis. 4. Have students do a photosynthesis presentation at a local Earth Day or nature festival. ETYMOLOGY OF KEY TERMS auto- self; occurring spontaneously (from the Greek autos- self) chloro- green (from the Greek chloros- light green or greenish yellow) hetero- different (from the Greek heteros- the other of two) meso- middle (from the Greek mesos- in the middle) photo- light (from the Greek photos- light) -phyll of, or pertaining to, a leaf (from the Greek phyllos- leaf) synthesis to make or assemble (from the Greek synthesis- placing together) -troph nutrient; nutritional requirement (from the Greek trophe- nourishment or food) CHAPTER 9: CELL COMMUNICATION WHERE DOES IT ALL FIT IN? Chapter 9 combines the information in Chapters 4 and 5 to provide a story about cellular interactions. These interactions are essential for understanding the signaling that controls gene expression. In addition, cell-cell interactions determine the success of multicellularity and promote the development of a fertilized egg into a normal embryo. This information should be reviewed when covering later chapters that cover cell signaling, embryology, endocrine system, and nervous system. SYNOPSIS Cells of multicellular organisms must communicate with one another so that they behave as a coordinated group of cells rather than just a bunch of independent ones. Recall the cliche “the left hand doesn’t know what the right hand is doing.” The signals to which a cell responds are dependent on the kinds of receptor proteins associated with that cell. If the signal is just the right molecular shape, it and the receptor bind eliciting a response somewhere in the cell. There are four main types of cell signaling. Direct contact and paracrine signaling are important in early organismal development. Endocrine signaling via hormones provides widespread response in both plants and animals. Synaptic signaling found in animal nervous systems produces more localized responses at the chemical synapse between the neuron and the receptor cell. Intracellular receptors are small molecules that are able to pass through the plasma membrane of the target cell. Nitrous oxide is one example. It activates the enzyme that catalyzes synthesis of cyclic GMP. A superfamily of steroid hormone receptors have specific DNA binding sites normally occupied by an inhibitory protein. When the signal molecule binds to another site on the receptor the inhibitor is released. The receptor then binds to DNA to activate or suppress a certain gene. There are three superfamilies of cell surface receptors. The signals associated with these receptors bind to receptor proteins on the cell surface. Thus an extracellular signal is converted to an intracellular signal. In chemically-gated ion channels the receptor is a transmembrane protein that winds back and forth through the membrane several times (called a multi-pass protein). The center of this protein forms a channel through which specific ions can pass. Enzymatic receptors are linked to enzymes or themselves act as enzymes. Most of these are protein kinases; they add phosphate groups to proteins. They are single pass transmembrane proteins where the region that binds with the signal molecule is located outside the cell and the portion that initiates enzymatic activity is found within it. G protein-linked receptors are seven-pass transmembrane proteins that become activated when they bind to GTP. These receptors are important because they provide the mechanism of action for over half of the therapeutic drugs currently in use. Second messengers are small molecules or ions that alter the shape and behavior of receptor proteins to relay the signal message to enzymes or genes within a cell. cAMP is the most widely used second messenger in animal cells. Ultimately the cAMP binds to A-kinase, activating it to phosphorylate certain cell proteins. Calcium is normally sequestered outside a cell or within its endoplasmic reticulum. With the proper G protein signal inositol triphosphate is eventually produced, which opens calcium channels in the ER membrane. This influx of calcium triggers many activities. In most cases, a cellular signal is too insignificant to result in an adequate cellular response. Protein kinase cascades amplify the signal. In vision for example, a single light-activated rhodopsin molecule activates many transducin molecules that further split 105 cyclic GMP molecules. LEARNING OUTCOMES 9.1 The Cells of Multicellular Organisms Communicate 1. Discriminate between methods of signaling based on distance from source to reception. 2. Define signal transduction pathway. 3. Differentiate between the activity of kinases and phosphatases. 9.2 Signal Transduction Begins with Cellular Receptor 1. Differentiate between different receptor types based on their cellular location. 9.3 Intracellular Receptors Respond to Signals by Regulating Gene Expression 1. Explain how steroid hormone receptors can affect transcription. 2. Differentiate between the action of NO and steroid hormones. 9.4 Protein Kinase Receptors Respond to Signals by Phosphorylating Proteins 1. Explain how autophosphorylation transmits a signal across the membrane. 2. Describe how protein-protein interactions transmit signals. 3. Differentiate between different types of receptors, based on their cellular location. 4. Describe the role of Ras protein in signaled transduction. 9.5 G Protein-Coupled Receptors Respond to Signals Through Effector Proteins 1. Describe how heterotrimeric G proteins are activated and inactivated. 2. Compare and contrast the action of different second messengers. 3. Explain how signals can converge and diverge in cells. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 9 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • The lipid layer is a solid surface • Cell membrane proteins are immoveable in the bilayer • Only hormones are cell signals • All hormones are related to steroids • Plants do not produce hormones • Neurotransmitter receptors are not the same as hormone receptors • All hormones act on cell surface receptors • Cell surface receptors are not associated with changes in gene expression INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Students need to be secure in the material from the previous chapter to progress in this one. There is a lot of new terminology. Flash cards will help the students learn this information — making them as much as using them. Table9.2 is an invaluable summary of the chapter, but too many students will use it as a crutch and just memorize it. It’s much better if they make their own table(s). The best part of the learning process is in the organization and gathering of information. Re-emphasize the importance of molecular binding to induce three-dimensional shape changes to effect a variety of changes within the cell. Stress the importance of protein kinases. The topic will come up again in gene expression and regulation. It’s amazing how a simple addition of a PO4 group can do so much in a cell! Don’t let your students confuse desmosomes and plasmodesmata. They sound similar, but are very different structures. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 9. Application • Have students predict would happen if a chemical that blocks cAMP were given to a culture of cells. • Ask students to determine the chemical nature of a hormone that affects a cell in spite of the presence of cell surface receptors for the hormone.. • Ask students to explain why insufficient calcium in the tissues affects cell interactions. Analysis • Ask students describe the properties of a chemical that blocks an intracellular receptor. • Have students explain how cell to cell communication will be affected by bathing cells in a solution of enzymes that degrade proteins. • Ask students explain why certain organisms that enter cells can only invade specific cells in an organism. Synthesis • Ask students come up with uses of a drug that inhibits the action of protein kinases in targeted cells. • Ask students to come up with commercial and food preparation uses for fungi known to degrade cell junction proteins. • Ask students to explain how genetic modification techniques that alter G-protein function can be used to produce new types of agricultural animals. Evaluation • Ask students to compare and contrast the cell surface receptors to proteins involved in active transport. • Ask students to evaluate a claim about a drug that increases alertness because it supplies phosphorus that fuels kinases of the brain cells. • Have students explain the validity of using oral ATP supplements to enhance cell signaling. VISUAL RESOURCES 1. The amplification analogy in the book is very straight forward, but students will quickly identify with the shampoo commercial where “you tell two friends and they tell two friends ... while they see on TV one person, then two, then four, and so on. You could also do a class demo on this, distributing note cards, rubber bands, or other small, inexpensive objects. 2. Make models of various cell–cell interactions using plastic, paper, string, straws, etc. Better yet, have your students make them, collect them, choose the best, and you will have models to show in class next semester! IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Cell Signaling Role Playing Introduction Molecular role playing is a fun and effective way to demonstrate complex concepts to students. This activity asks students to demonstrate the differences between cell communication systems. Use this activity to help students summarize and review the events of cell signaling. Materials • Colored markers • Sheets of 8 ½” X 11” white paper • Students volunteers • 2 15’ sections of rope of twine • Scissors • 10 feet of thick tubing • Ample space to move around Procedure and Inquiry 1. Tell students that they are to plan a play in which they will be role modeling the mechanisms of cell to cell communication. 2. Ask them to use the rope to represent the cell membrane of an individual cell, the tubing to depict a blood vessel, and each student will represent a cell structure involved in cell signaling. They must use the marker and paper to label the role of each individual who is demonstrating a cell signaling structure. 3. First, instruct the students to role play the four basic mechanisms of cell communication: direct contact, paracrine signaling, endocrine signaling, or synaptic signaling. 4. Have the students discuss the accuracy of their role model. 5. Next, ask the students to role play intracellular receptor cell signaling. 6. Have the students discuss the accuracy of their role model. 7. Then, ask the students to role play cell surface receptor cell signaling. 8. Have the students discuss the accuracy of their role model. 9. Recap the activity by asking how such demonstrations may be useful for researchers investigating cell signaling mechanisms. LABORATORY IDEAS A. Response to Cell Signals a. Have students investigate the signaling response of an animal model to adrenalin. b. This laboratory activity looks at the effect of adrenalin as a signal that affects the metabolic rate of particular cells. c. Provide students with the following materials: i. Daphnia kept in a container of clean fresh water ii. A large container of clean water for used daphnia iii. Droppers for collecting and transporting the daphnia iv. Microscope v. Microscope slides per observation vi. Droppers for transporting chemicals vii. Over-the-counter epinephrine preparation (asthma pills) soaked in 100ml of a 50% ethyl alcohol/50% water mixture viii. Surgical gloves and goggles d. Have the students carry out the following procedure: i. Ask the students to place some daphnia on the microscope slide and observe their normal behavior ii. Make sure they keep adding water to the slide to keep the daphnia from drying out and dying iii. Have them keep track of the speed at which they are moving around how fast they move their feet. iv. Then have the students add one drop of the epinephrine solution to the daphnia v. The students should note what happens to movement of the daphnia vi. Have the students repeat steps iv and v several times vii. Students should then be asked to investigate how adrenalin works as a cell signal and whether their observations were consistent with findings on other organisms viii. Ask students to investigate the types of cells and tissues in the daphnia that are response to the adrenalin B. Comparative Response to Cell Signals a. Have students investigate the specificity of cell signaling responses of an animal and a plant. b. This laboratory activity looks at the differential effects of caffeine and adrenalin as a signal that may or may not affect the metabolic rate of cells. c. Provide students with the following materials: i. Daphnia kept in a container of clean fresh water ii. Elodea kept in a container of clean fresh water iii. Droppers for collecting and transporting the daphnia iv. Forceps for transporting the elodea v. Microscope vi. Droppers for collecting samples of epinephrine and caffeine vii. 2 clean microscope slides per observation viii. Over-the-counter epinephrine preparation (asthma pills) soaked in 100ml of a 50% ethyl alchohol/50% water mixture ix. 100mg caffeine pill soaked in 100ml of a 50% ethyl alchohol/50% water mixture x. Surgical gloves and goggles d. Have the students carry out the following procedure: i. Ask the students to place some daphnia and elodea on the same microscope slide ii. Observe their normal behavior and the cytoplasmic streaming of the elodea iii. Make sure the students keep adding water to the slide to keep the daphnia and elodea from drying out and dying iv. Have them keep track of the speed at which the daphnia and the cytoplasmic are moving. v. Then have the students add two drops of the epinephrine solution to the slide vi. The students should note what happens to the daphnia and the elodea vii. Next, ask the students to place some daphnia and elodea together on a new microscope slide viii. Then have the students add two drops of the caffeine solution to the slide ix. The students should note what happens to the daphnia and the elodea x. Students should then be asked to investigate the effects of adrenalin and caffeine on the cells. They should use the Internet or other resources to see how each works as a cell signal. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. Students who have successfully mastered the content of Chapter 9 can apply their knowledge for service learning activities in the following ways: 1. Have students talk to youth sports groups about how steroids affect cell function. 2. Have students design an electronic animated presentation on cell signaling for teachers at local schools. 3. Have students tutor middle school or high school biology students studying cell function. 4. Have students talk to the elderly about “youth drugs” that rely on cell signaling such as growth hormone or estrogens. ETYMOLOGY OF KEY TERMS auto- self; occurring spontaneously (from the Greek autos- self) -crine secreting or secretion (from the Greek krinein- to separate or secrete) cyto- of, or relating to, the cell (from the Greek kytos- cell) -duct to carry (from the Latin ductere- to lead or draw forth) epi- above; over (from the Greek epi- on, over, near, at, or before) -kinesis movement (from the Greek kinein- to move) liga- binding; attaching (from the Latin ligare- to bind or tie) mito- thread (from the Greek mitos- a thread) nephr(i)- pertaining to kidneys (from the Greek nephros- kidney) para- beside; next to (from the Greek para- beside) photo- light (from the Greek photos- light) trans- across, through (from the Latin trans- across or through) -tropism orientation or turning toward (from the Greek tropos- turning) Instructor Manual for Understanding Biology Kenneth Mason, George Johnson, Jonathan Losos, Susan Singer 9780073532295, 9781259592416