Chapter 8 Making energy! ATP The point is to make ATP!

5.12 Chemical reactions either release or store energy An exergonic reaction is a chemical reaction that releases energy This reaction releases the energy in covalent bonds of the reactants Burning wood releases the energy in glucose, producing heat, light, carbon dioxide, and water Cellular respiration also releases energy and heat and produces products but is able to use the released energy to perform work A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when weather is warm. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.) Copyright © 2009 Pearson Education, Inc.

Amount of energy released Reactants Amount of energy released Potential energy of molecules Energy released Products Figure 5.12A Exergonic reaction, energy released.

5.12 Chemical reactions either release or store energy An endergonic reaction requires an input of energy and yields products rich in potential energy The reactants contain little energy in the beginning, but energy is absorbed from the surroundings and stored in covalent bonds of the products Photosynthesis makes energy-rich sugar molecules using energy in sunlight Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.) Copyright © 2009 Pearson Education, Inc.

Amount of energy required Products Amount of energy required Potential energy of molecules Energy required Reactants Figure 5.12B Endergonic reaction, energy required.

The energy needs of life Organisms are endergonic systems What do we need energy for? synthesis building biomolecules reproduction movement active transport temperature regulation Which is to say… if you don’t eat, you die… because you run out of energy. The 2nd Law of Thermodynamics takes over! A living organism produces thousands of endergonic and exergonic chemical reactions All of these combined is called metabolism A metabolic pathway is a series of chemical reactions that either break down a complex molecule or build up a complex molecule Metabolism requires energy, which is taken from sugar or other molecules containing energy. A cell does three main types of cellular work Chemical work—driving endergonic reactions Transport work—pumping substances across membranes Mechanical work—beating of cilia To accomplish work, a cell must manage its energy resources, and it does so by energy coupling—the use of exergonic processes to drive an endergonic one ATP is responsible for mediating most energy coupling in cells.

Sunlight energy Photosynthesis in chloroplasts + + (for cellular work) ECOSYSTEM Photosynthesis in chloroplasts CO2 Glucose + + H2O O2 Cellular respiration in mitochondria Figure 6.1 The connection between photosynthesis and cellular respiration. ATP (for cellular work) Heat energy

Where do we get the energy from? Work of life is done by energy coupling use exergonic (catabolic) reactions to fuel endergonic (anabolic) reactions digestion energy + + synthesis energy + +

ATP Living economy Fueling the body’s economy eat high energy organic molecules food = carbohydrates, lipids, proteins, nucleic acids break them down digest = catabolism capture released energy in a form the cell can use Need an energy currency a way to pass energy around need a short term energy storage molecule ATP Whoa! Hot stuff!

ATP Adenosine TriPhosphate modified nucleotide nucleotide = adenine + ribose + Pi  AMP AMP + Pi  ADP ADP + Pi  ATP adding phosphates is endergonic Marvel at the efficiency of biological systems! Build once = re-use over and over again. Start with a nucleotide and add phosphates to it to make this high energy molecule that drives the work of life. Let’s look at this molecule closer. Think about putting that Pi on the adenosine-ribose ==> EXERGONIC or ENDERGONIC? ATP, adenosine triphosphate, is the energy currency of cells. ATP is the immediate source of energy that powers most forms of cellular work. It is composed of adenine (a nitrogenous base), ribose (a five-carbon sugar), and three phosphate groups. The phosphate group serves as a functional group, and the hydrolysis of this group releases energy. ATP is also one of the nucleoside triphosphates used to make RNA. How efficient! Build once, use many ways high energy bonds

5.13 ATP shuttles chemical energy and drives cellular work Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule The transfer is called phosphorylation In the process, ATP energizes molecules For the BLAST Animation ATP/ADP Cycle, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips 1. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.) 2. When introducing ATP and ADP, consider having them think of the terms as A-3-P and A-2-P, noting that the word roots tri- = 3 and di- = 2. It might help students to keep track of the number of phosphates more easily. 3. Recycling is essential in cell biology. Damaged organelles are broken down intracellularly and chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. Both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). Copyright © 2009 Pearson Education, Inc.

Adenosine Triphosphate (ATP) Phosphate group Adenine Ribose Hydrolysis Figure 5.13A The structure and hydrolysis of ATP. The reaction of ATP and water yields ADP, a phosphate group, and energy. + Adenosine Diphosphate (ADP)

Phosphorylation Hydrolysis Energy from exergonic reactions Energy for endergonic reactions Figure 5.13C The ATP cycle. ATP is a renewable source of energy for the cell When energy is released in an exergonic reaction, such as breakdown of glucose, the energy is used in an endergonic reaction to generate ATP For the BLAST Animation Structure of ATP, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips 1. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.) 2. When introducing ATP and ADP, consider having them think of the terms as A-3-P and A-2-P, noting that the word roots tri- = 3 and di- = 2. It might help students to keep track of the number of phosphates more easily. 3. Recycling is essential in cell biology. Damaged organelles are broken down intracellularly and chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. Both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population).

Membrane protein Chemical work Mechanical work Transport work Solute Motor protein Membrane protein Reactants Figure 5.13B How ATP powers cellular work. Product Molecule formed Protein moved Solute transported

How does ATP store energy? I think he’s a bit unstable… don’t you? P O– O –O P O– O –O P O– O –O P O– O –O P O– O –O ADP AMP ATP Each negative PO4 more difficult to add a lot of stored energy in each bond most energy stored in 3rd Pi 3rd Pi is hardest group to keep bonded to molecule Bonding of negative Pi groups is unstable spring-loaded Pi groups “pop” off easily & release energy Not a happy molecule Add 1st Pi  Kerplunk! Big negatively charged functional group Add 2nd Pi  EASY or DIFFICULT to add? DIFFICULT takes energy to add = same charges repel  Is it STABLE or UNSTABLE? UNSTABLE = 2 negatively charged functional groups not strongly bonded to each other So if it releases Pi  releases ENERGY Add 3rd Pi  MORE or LESS UNSTABLE? MORE = like an unstable currency • Hot stuff! • Doesn’t stick around • Can’t store it up • Dangerous to store = wants to give its Pi to anything Instability of its P bonds makes ATP an excellent energy donor

How does ATP transfer energy? + ATP ADP ATP  ADP releases energy ∆G = -7.3 kcal/mole Fuel other reactions Phosphorylation released Pi can transfer to other molecules destabilizing the other molecules enzyme that phosphorylates = “kinase” How does ATP transfer energy? By phosphorylating Think of the 3rd Pi as the bad boyfriend ATP tries to dump off on someone else = phosphorylating How does phosphorylating provide energy? Pi is very electronegative. Got lots of OXYGEN!! OXYGEN is very electronegative. Steals e’s from other atoms in the molecule it is bonded to. As e’s fall to electronegative atom, they release energy. Makes the other molecule “unhappy” = unstable. Starts looking for a better partner to bond to. Pi is again the bad boyfriend you want to dump. You’ve got to find someone else to give him away to. You give him away and then bond with someone new that makes you happier (monomers get together). Eventually the bad boyfriend gets dumped and goes off alone into the cytoplasm as a free agent = free Pi.

An example of Phosphorylation… Building polymers from monomers need to destabilize the monomers phosphorylate! H OH C H HO C enzyme C H OH HO O + H2O synthesis +4.2 kcal/mol + ADP C H OH “kinase” enzyme C H P Monomers  polymers Not that simple! H2O doesn’t just come off on its own You have to pull it off by phosphorylating monomers. Polymerization reactions (dehydration synthesis) involve a phosphorylation step! Where does the Pi come from? ATP It’s never that simple! + ATP -7.3 kcal/mol C H P H HO C + C H O + Pi -3.1 kcal/mol

Another example of Phosphorylation… The first steps of cellular respiration beginning the breakdown of glucose to make ATP glucose C-C-C-C-C-C Those phosphates sure make it uncomfortable around here! C H P ATP 2 hexokinase ADP 2 phosphofructokinase These are the very first steps in respiration — making ATP from glucose. Fructose-1,6-bisphosphate (F1,6bP) Dihydroxyacetone phosphate (DHAP) Glyceraldehyde-3-phosphate (G3P) 1st ATP used is like a match to light a fire… initiation energy / activation energy. The Pi makes destabilizes the glucose & gets it ready to split. fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P activation energy

ATP / ADP cycle Can’t store ATP ATP good energy donor, not good energy storage too reactive transfers Pi too easily only short term energy storage carbohydrates & fats are long term energy storage ATP cellular respiration 7.3 kcal/mole ADP Pi + A working muscle recycles over 10 million ATPs per second Whoa! Pass me the glucose (and O2)!