Chapter+Eight

BIOL 160: General Biology Definition Worksheet #9: Chapter 8 Define the following terms related to cellular respiration. 1. Absorptive State 2. Aerobic Respiration 3. Alcohol Fermentation 4. Anaerobic Respiration 5. Cellular Respiration 6. Electron Transport Chain 7. Glucose 8. Glycogen 9. Glycolysis 10. Kreb's Cycle 11. Lactic Acid Fermentation 12. NADH and FADH 2 13. Oxidative Phosphorylation 14. Post-Absorptive State 15. Pyruvate 16. Substrate-level Phosphorylation


 * __ CHAPTER 8 __**** : How Cells Release Stored Energy **

1. All living organisms, regardless of how small use energy on a regular basis. So where do they get the energy? A. Plants (also known as producers) make ATP during the process of photosynthesis and then use that energy to drive chemical reactions that convert CO2 and H2O into glucose (C6H12O6) which most of them store as the large complex carbohydrate molecules called. (Remember from module 2?). B. Humans get their energy second or third hand from eating plants or other animals that have eaten the plants. Regardless of the source, the body ultimately converts the energy stored in carbohydrates, lipids and proteins back into the form of ATP molecules that the cells can use on the molecular level. 2. There are two main types of energy-releasing pathways used by cells: A. _ Pathway: this method of producing energy evolved first. It occurs in the cytoplasm of the cell and does NOT require oxygen. Many prokaryotes (bacteria) still live in places where there is a very limited oxygen supply and still rely on this pathway for producing energy. There are also times when the oxygen supply to some cells in the body is not great enough to meet the cellular demands for energy so cells must rely on this method as well. B. _ Pathway: this method evolved later and is the main pathway used by the cells in the body to produce the needed energy. This pathway requires an adequate supply of oxygen to operate successfully and begins in the cytoplasm but continues in the __. The pathway is divided into three parts or stages:__ __1.__ __: occurs in the cytoplasm and involves a series of reactions that breaks a glucose molecule into two smaller pyruvate (pyruvic acid) molecules and in the process also produces 2 ATP molecules.__ __2.__ ___ CYCLE: occurs in the inner membrane spaces (matrix) of the mitochondria and involves a series of reactions that removes all remaining hydrogen atoms with their electrons from the carbon chain and in the process also produces 6 CO2 and 2 ATP molecules.__ __3.__ __PHOSPHORYLATION: occurs along the inner mitochondrial membrane and involves a series of chemical reactions that remove the electrons from the hydrogen atoms and uses the potential energy of a concentration gradient to drive the production of ATP molecules and in the process produces 6 H2O and 32-34 ATP molecules.

3. Overview of Aerobic (Cellular) Respiration:


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[|http://www.mansfield.ohio-state.edu/~sabedon/biol1100.htm] Great link that has details about respiration PLUS a very succinct energy accounting!!! A. Aerobic respiration starts with **1** glucose molecule and produces a total energy yield of **36** ATP or more. B. The following is the overall chemical reaction for cellular respiration:

1 C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP Glucose + Oxygen → Carbon dioxide + Water + Energy

C. The overall process involves over 30 different reactions producing specific intermediate molecules along the way. You will NOT need to remember all of these by name, only a few very select molecules. D. Each chemical reaction requires a specific enzyme (you don’t need to know these by name either) and several very important co-enzymes (NAD+ and FAD) that function to “carry” the Hydrogen atoms to the final stage of the pathway. Because of their function, these coenzymes are often called “carrier” or “transport” molecules.

4. **Glycolysis**_: The First Stage of cellular respiration (the Energy- releasing Pathway). These reactions take place entirely in the cytoplasm and occurs in two stages:  A. Energy **releasing** Steps: Two **ATP**_ molecules found in the cytoplasm of the cell are used to activate the incoming **glucose**___ molecule__ __and in a sense “traps” it in the cell to__ __ensure the concentration gradient is__ __maintained and to rearrange the molecule__ __to make it more symmetrical (balanced)__ __so it will be easier to break in half.__

__B. Energy **releasing**__ ___ Steps:__ __ The product of the first stage is split into__ __two three-carbon molecules called **PGAL**__ __that are further__ __modified by removing a hydrogen atom__ __from each and transferring them to two__ __NAD molecules forming__ _**NADH** and replacing the hydrogen atoms with two phosphate groups. Eventually the phosphate groups are removed and transferred to ADP molecules forming a total of four ___molecules and two__ __molecules of **pyruvate**__ _____ __(pyruvic acid) as the end products of this__ __series of reactions.__ __The PGAL molecules are important intermediate molecules as they serve as a location where part of the triglyceride molecules can enter the pathway to be used to produce ATP energy. And the 2PGA or BPG molecules are important as they influence whether hemoglobin molecules in red blood cells will keep or release oxygen to the tissue.__ __When ATP molecules are produced in the absence of oxygen by transferring phosphate groups from the substrate molecules (reactants) to ADP molecules, the__ __process is called **substrate-level**__ PHOSPHORYLATION.

In review: The following are the key points to remember about Glycolysis. The initial reactant was **glucose**_. Two molecules of **ATP** _ were added helping to trap and rearrange the molecule to make it easier to break in half. Eventually **4**_ ATP molecules were produced, resulting in a net gain overall of ___**2** ATP, and **2**_____ NADH molecules (to be used later by the__ __mitochondria to produce even more ATP) as well as two molecules of the final__ __product__ __. These series of reactions do not rely on the presence of oxygen, so they can occur in an anaerobic situation when oxygen levels are low.__ __5. **KREBS**__ __CYCLE (Citric Acid Cycle): The Second Stage of cellular respiration (the Energy-releasing Pathway).__ __These reactions take place entirely in the inner compartment or inner membrane space (matrix) of the mitochondria and also occur in two stages:__ __A. The **Acytel CoA**___Formation Stage:  Remember that Glycolysis ended with the production of 2 **pyruvate** (pyruvic acid) molecules; therefore all reactions in this step are doubled. The pyruvate molecules are oxidized into two 2-carbon molecules with the help of a special enzyme helper called “Coenzyme A” producing two molecules of Acetyl Co-A. In the process, a total of another **2** __NADH molecules were produced as__ __well as **2**__ CO2 molecules that are waste products.  B. KREBS CYCLE proper: Because there were two Acetyl-CoA molecules produced in preparing to enter the cycle, all reactions here are also doubled. The remaining **hydrogen** __atoms are removed and__ __given to the “carrier molecules” NAD+ and FAD__ __producing an additional **6**__ NADH and __**2** FADH2 molecules that will later be__ __used by the mitochondria to produce even__ __more ATP molecules. In addition to the__ __“carrier molecules” produced, an additional__ CO2 molecules and **2**_ ATP are produced by a process called substrate-level phosphorylation.

Even though these series of reactions do not rely on the presence of oxygen directly, the main products produced (NADH and FADH2) will be sent to the last stage of cellular respiration that DOES require oxygen and therefore Krebs Cycle will only occur in an aerobic situation when oxygen levels are high. In review: The following are the key points to remember about Krebs Cycle. The process began with two molecules of **pyruvate** _ that were produced by the break-down of one glucose molecule so all reactions are actually doubled (once for each of these molecules). In the initial reactions, two hydrogen atoms were removed forming two molecules of **NADH** and two molecules of **CO2** __that are waste products, as well as two molecules__ __of **Acetyl-CA**_____ that will enter Krebs cycle proper. During the__ __final series of reactions,**2**__ ___ more NADH will be produced for a total__ __of **6**_____ NADH,__ FADH2, four more molecules of **CO2** __that are waste products for a total of **6**__ CO2 as well as **2** ___ ATP by a process called substrate-level phosphorylation.__

__6. **Oxidative**__ PHOSPHORYLATION: The third Stage of cellular respiration (the Energy-releasing Pathway), is also known as the electron transport chain (since it involves the removal of electrons from the hydrogen atoms), or oxidative phosphorylation (since oxygen is required to make ATP). A. These reactions takes place along the inner-mitochondrial membrane. The coenzyme carrier molecules NADH and FADH2 deliver the Hydrogen atoms to specialized enzymes (embedded in the membrane) that will remove the electrons and use the potential energy to drive the production of **ATP**_ molecules. B. The “Chemiosmosis Theory” attempts to explain how this process occurs. 1. When the hydrogen atoms are delivered to the specialized enzymes in the membrane, the enzymes remove the electron and as it is passed along from enzyme to enzyme the action produces enough energy to transfer the unbound hydrogen ions (H+1) to the outer compartment of the mitochondria creating a concentration gradient of hydrogen ions.
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2. Also embedded in the inner-mitochondrial membrane are very specialized transporter (channel) proteins called ATP **synthase** _ that allow the Hydrogen ions (H+1) that have a high concentration in the outer compartment to move down their concentration gradient into the inner compartment. The movement of the H+1 ions through these proteins provides the needed energy to drive the phosphorylation of ADP into ATP. 

3. At the end of the electron transport system the electrons need to go somewhere. Remember from chapter 2 that some elements are “takers” of electrons and some are “givers”. The element oxygen was classified as a **taker** __. Oxygen atoms take the electrons from the transporter enzymes becoming a negative ion (O-2) at which point it is immediately attracted to some of the hydrogen ions (H+1) and the two join__ __together to produce a molecule of **water**__. To put it another way, __**product**_ along with the ATP molecules.__ __7. Anaerobic Energy-Releasing Pathways:__ __A. Unlike aerobic respiration, the anaerobic pathways do not use oxygen in the last steps as the final electron acceptor; their final steps have the important function of regenerating NAD+ “carrier molecules.__ __1. Without an adequate supply of oxygen there would be no place for the electrons to go, so the electrons would “build up” in the electron transport chain, and soon the NADH and FADH2 would not be able to release their Hydrogen atoms, essentially shutting down this stage.__ __2. If the carrier molecules were not able to release the hydrogen, soon there would be no more available to “take” the hydrogens released in Krebs cycle, essentially shutting down that stage as well.__ __3. If Krebs cycle “shuts down” it seems logical that Glycolysis would shut down as well; however, the cell must have at least__ some __ATP to stay alive!__ __B. Without an adequate supply of oxygen,__ only __the first stage (Glycolysis) can occur. Each glucose molecule will produce a total of only 2ATP rather than 36 ATP when oxygen is readily available. This is not a very good use of glucose but 2 ATP molecules are better than none and this works fine for a short time. The problem is that the NADH produced have no where to go (remember the electron transfer chain is shut down without oxygen) and will eventually need to be recycled.__ __C. There are two processes that can recycle the NADH back into NAD+1.__ __1. **Alcohal**__ _ FERMENTATION: a. This process is used by yeast and other anaerobic organisms to produce energy when oxygen levels are low. b. This process also uses Glycolysis as the first step to produce 2 ATP, but the rest of the energy-releasing pathways are shut down so because there is no place to send the Pyruvic acid molecules, and the supply of NADH will run out, the cell uses these molecules to produce Carbon dioxide gas and Ethanol (ethyl alcohol).  c. Yeast is used in baking bread because the yeast uses this form of respiration for their energy supply and in the process produce CO2 which is what causes the bread to rise.
 * oxygen** is the final electron acceptor and water is the final

d. Ethanol in large quantities is toxic and eventually the cells will die, which is why this method is NOT used by our bodies to generate more NAD+ when oxygen levels are low.

2. FERMENTATION: a. This process occurs especially in muscle cells when the demand for energy is intense but brief, as in sprinting or lifting weights. b. Special enzymes remove the hydrogen atoms from the NADH and give it back to the pyruvate molecule converting it into a lactate (lactic acid) molecule, and in the process the NAD+ is regenerated so glycolysis can continue.  c. It is not the most efficient use of glucose and as the supply of glucose is depleted the muscle will fatigue (get tired) and lose their ability to contract.

d. Some muscle cells (muscle fibers) must be able to stay contracted for a long period of time to keep the body or body part upright, such as your back and neck muscles or be able to contract repeatedly for an extended period of time, as in the leg muscles of marathon runners. Cells capable of these activities are called __muscle fibers, and make ATP only by aerobic respiration. This means they must have a__ __large number of__, and a constant supply of oxygen. Muscles containing this type of cells appear dark in color due to the increased blood supply and the presence of a protein that stores the oxygen until needed, hence the term “dark” meat. e. Some muscle cells (muscle fibers) must be able to contract very quickly and forcefully, as in jumping, throwing a “fast pitch” ball or a reflex reaction as when touching a hot object. Cells capable of these activities are called muscle fibers, and use the process of Lactate Fermentation (anaerobic respiration) to make ATP; therefore these cells have very few mitochondria. The pathway makes ATP very quickly but not for very long. It is not an effective use of glucose (2 ATP verses 36 ATP). Muscles containing this type of cells do not have a rich blood supply and do not store oxygen, so appear light in color, hence the term “light” or “white” meat.

8. Alternative Energy Sources in the Human Body A. This chapter has concentrated on the use of glucose for the production of ATP energy because it is the body’s preference as an energy source. When glucose levels are high, the cell makes as much ATP as possible to have it available if the cell should need it in the future. Once the ATP levels get high enough (especially in the muscle and liver cells), the glucose is used to make other molecules like glycogen and triglycerides to store the energy for later use. 1. Energy from GLYCOGEN stored in the liver and skeletal muscles: a. When blood sugar levels decline, the pancreas releases the hormone glucagon (glucose is almost gone). b. Liver cells are stimulated to break down the glycogen back into glucose and release it to the blood. Muscle cells are also stimulated to break down the glycogen, but they keep the glucose for themselves and do not release it into the blood. c. Polysaccharides like glycogen and starch have the potential of generating 4 kilocalories of energy per gram. 2. Energy from FATS (Triglycerides) stored in adipose cells: a. The triglycerides are broken down into their component parts: 1. The 3-carbon glycerol backbone enters at the half-way point of _ and continues through the rest of the cellular respiration pathways as though it started out as glucose. 2. The fatty acid molecules (tails) are broken down with the help of a coenzyme into acetyl-Co A molecules that enter _ and continue through the rest of the cellular respiration pathways as though they started out as glucose. b. Fats have a much higher concentration of hydrogen atoms than carbohydrates and proteins and therefore more electrons and more energy potential. c. They are also much less dense (are lighter) so gram for gram fats have the potential of generating more than twice the amount of energy as either carbohydrates or proteins, in fact fats have the potential of generating 9 kilocalories per gram. 3. Energy from Proteins: a. The proteins are first broken down into their monomers (building blocks) called ___.__ __b. The amino functional group is removed from the carbon atoms and excreted from the body as part of urine.__ __c. The carbon fragment that remains generally enters somewhere in__ __, depending on the number of carbon atoms in the group and continues through the pathway as though it started out as glucose.__ __d. Proteins like carbohydrates are able to produce 4 kilocalories of energy per gram.__ __B. During any 24-hour period, the body experiences two broad patterns of metabolic activity: the //absorptive state// and the //postabsorptive state.//__ __1. ABSORPTIVE STATE of metabolism: this is the period of time after consuming a meal (about 4 hours) when the body is absorbing nutrients from the digestive system. Some of the monomers are used immediately for energy; however the vast majority is stored for future use between meals, like when we are sleeping. The main reactions occurring at this time are classified__ __as__ //_____// __(the building of large molecules from small ones) for growth of tissue and storage of energy reserves for future use.__ __2. POSTABSORPTIVE STATE of metabolism: this is the period of time when nutrients are NOT being absorbed from the digestive system and the body must rely on internal energy reserves. The main reactions occurring at this__ __time are classified as__ //___// (the breaking down of large molecules into smaller ones). Generally during this time, the goal is to maintain energy levels in the body. The glucose supply has dropped significantly so the body shifts from glucose catabolism to fatty acid and protein catabolism to obtain energy.

9. Just a few more points that need to be emphasized, then you’re done! A. The overall reaction of cellular respiration is 1 C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP however no chemical reaction is ever 100% efficient. Our bodies are only able to capture about 40% of the total potential energy stored in a glucose molecule; the rest is lost as heat. This is why when you exercise, your cells need more energy so the rate of cellular respiration increases and more heat is produced, your body begins to overheat and you start sweating to try to lower the body temperature. B. The energy-releasing pathways discussed in this chapter are also known as CELLULAR RESPIRATION. It is called this because the word respiration means the exchange of gases. The respiratory system in the body is responsible for taking in oxygen from the air and releasing carbon dioxide produced by the body. It has been shown that oxygen is critical to the efficient production of ATP from glucose, so cells must take in oxygen from the blood and use it to make ATP. It has also been shown that CO2 is produced as a waste product and the cell must eliminate it so in a sense the cells are “breathing” or exchanging gases just like the lungs. C. All molecules (chemicals) have stored potential energy in the electrons located in their bonds. The goal of cellular respiration is to get at those electrons and use them to drive the production of ATP. To capture the electrons, hydrogen atoms must be separated from the carbon and oxygen so bonds must be broken, which releases heat. Remember, the hydrogen atom is the “weakest” of all the atoms in keeping the electron so it is the target of cellular respiration; if some other element was keeping the electron it may not give it back. The carrier molecules NAD+ and FAD are responsible for making sure the Hydrogen (with the electron) make it to their final destination (the electron transport chain). D. Any substance that loses a hydrogen (or electron) is being OXIDIZED. Therefore glucose and all the intermediate molecules are being oxidized. Each of these molecules is losing some of their potential energy each time they lose or give away a hydrogen atom. The “carrier molecules” NAD+ and FAD are being REDUCED when they take the hydrogen atoms, which means they are “absorbing” more potential energy until they release the electron at the electron transport chain. The oxygen atom is the final electron acceptor, so it also is described as being REDUCED in the process of cellular respiration. Remember, any time a bond is formed, the substance is being REDUCED (more potential energy) and any time a bond is breaking, the substance is being OXIDIZED (less potential energy).

REVIEW ACTIVITIES:

10. Glycolysis is the first of three steps in cellular respiration. Review glycolysis by matching each phrase on the right with a term on the left. Some terms are used twice.

_ 2. Not involved in glycolysis _ 3. Fuel molecule broken down in glycolysis _ 4. Produced by substrate-level phosphorylation _ 5. Invested to energize glucose molecule at start of process _ 6. Reduced as glucose is oxidized _ 7. Glucose converted to two molecules of this _ 8. Assembled to make ATP _ 9. “Splitting of sugar” _ 10. Carries hydrogen and electrons from oxidation of glucose || A. NADH B. Pyruvic acid C. ATP D. NAD+ E. Glucose F. Glycolysis G. ADP and P H. Oxygen I. Intermediate ||
 * _ 1. Compound formed between glucose and pyruvic acid

11. Check your overall understanding of cellular respiration by matching each of the phrases below with one of the stages of the process. Assume in each case that you originally started with one glucose molecule. (Some may require more than one letter.) A. Glycolysis B. Krebs’ Cycle and the Preparatory Steps C. Electron Transport Chain (oxidative phosphorylation) D. Lactic Acid Fermentation

_ 1. Generates most of the ATP formed by cellular respiration _ 2. Begins the oxidation of glucose _ 3. Occurs outside the mitochondrion _ 4. Oxygen combines with H+ to form water molecules. _ 5. Oxidizes NADH and FADH2, producing NAD+ and FAD _ 6. Pyruvate is a reactant. _ 7. Where electrons and hydrogen combine with O2 to form H2O _ 8. Occurs along the inner mitochondrial membrane _ 9. Generates most of the CO2 produced by cellular respiration _ 10. FADH2 and NADH deliver hydrogen ions and electrons to this stage. _ 11. ATP synthase makes ATP. _ 12. Reduces NAD+ and FAD, producing NADH and FADH2 _ 13. Oxidative phosphorylation occurs to form ATP molecules. _ 14. The carbon atoms in pyruvate leave as CO2 molecules. _ 15. Oxidation and reduction reactions occur. _ 16. Coenzyme A binds to a two-carbon acetyl group. _ 17. Two NAD+ molecules form in the absence of oxygen. _ 18. Two FADH2 and ten NADH are sent to this stage _ 19. Lactic acid is an end product _ 20. Water is one of the major products _ 21. Occurs within the mitochondrion _ 22. Two FADH2 and eight NADH form. _ 23. Hydrogen ions collect in the mitochondrion’s outer compartment. _ 24. Hydrogens and electrons are transferred to NAD+ and FAD. _ 25. Two ATP molecules form by substrate-level phosphorylation. _ 26. Oxygen is a major reactant _ 27. No oxygen is required for ATP to be produced. _ 28. Thirty-two to thirty-four ATPs are produced. _ 29. NAD+ → NADH _ 30. Carried out by enzymes in the matrix (fluid) of the mitochondrion

12. Choose the one most appropriate answer for each.

2. _ oxygen 3. _ mitochondrion 4. _ electron transport phosphorylation 5. _ enzymes 6. _ ATP 7. _ glycolysis 8. _ aerobic respiration 9. _ cytoplasm 10. _ fermentation pathways || A. Starting point for three energy-releasing pathways B. The overall process by which cells use oxygen to make the vast majority of the ATP needed C. Site of glycolysis D. Third and final stage of aerobic respiration; highest ATP yield generated E. Oxygen is not the final electron acceptor F. Catalyze each reaction step in the energy-releasing pathways G. Second stage of aerobic respiration; pyruvate is broken down to CO2 and H2O H. Site of the aerobic pathway I. The final electron acceptor in aerobic pathways J. The energy form that drives metabolic reactions ||
 * 1. _ Krebs cycle

13. Compare the two mechanisms that generate ATP in cellular respiration—oxidative phosphorylation and substrate-level phosphorylation. A. In what stage(s) of cellular respiration does each occur?

B. Where does each get the energy for making ATP?

C. Which one produces the most ATP under aerobic conditions?

D. Which one produces the most ATP under anaerobic conditions?


 * //Sample test questions for chapter 8://**

1. Cellular respiration oxidizes sugar and produces ATP in three main stages: a. diffusion, passive transport and active transport b. glycolysis, lactic acid fermentation, alcoholic fermentation c. Krebs cycle, acetyl CoA, ATP d. Glycolysis, Krebs cycle, electron transport chain

2. During “REDOX” reactions a. the loss of electrons from one substance is called reduction b. a substance that gains electrons is said to be oxidized c. electrons are lost from one substance and added to another substance d. protons from one molecule replace the electrons lost from another molecule e. A, B and C

3. Which of the following statements differentiates substate-level phosphorylation from chemiosmotic (oxidative) phosphorylation? a. a phosphate group is transferred directly from a metabolic intermediate to ADP forming ATP b. it does not require the electron transport chain c. it can occur in the absence of oxygen d. it can occur outside the mitochondria e. all of the above

4. During which of the following phases of cellular respiration does substrate-level phosphorylation take place? a. glycolysis b. the Krebs cycle c. electron transport chain d. both A and B

5. The end products of glycolysis include a. FADH2 b. NADH c. Acetyl CoA d. glucose e. CO2

6. In the respiratory electron transport chain, electrons pass from one electron transport molecule to another and are finally accepted by a. a molecule of CO2 b. a molecule of water c. an oxygen atom d. ADP e. ATP

7. When a fatty acid molecule is used for aerobic respiration, it is converted into __, which is fed into__ __.__ __a. glucose……..glycolysis__ __b. glyceraldehyde-3-phosphate…….glycolysis (partway through)__ __c. acetyl CoA…….the Krebs cycle__

__8. The body’s preferred source of energy is/are__ __a. triglycerides__ __b. proteins__ __c. glycerol__ __d. macrominerals__ __e. glucose__

__9. The end product(s) of the electron transport chain is/are__ __a. ATP__ __b. ATP and CO2__ __c. pyruvic acid__ __d. ATP and water__ __e. ATP and O2__

__10. Each NADH is capable of producing how many ATP from the Electron Transport Chain?__ __a. 1__ __b. 2__ __c. 3__ __d. 30__ __e. 36__

__11. Under anaerobic conditions, muscle cells produce__ __ from the glucose as it is producing ATP energy. a. ethyl alcohol b. pyruvate c. lactic acid d. glycogen

12. Which of the following processes occurs inside the mitochondria? a. Kreb’s Cycle b. Electron Transport Chain c. Glycolysis d. A and B e. A, B and C

13. In which of the following processes does substrate level phosphorylation occur? a. Kreb’s Cycle b. Glycolysis c. Electron Transport Chain d. A and B e. A, B and C

14. Most of the ATP is produced a. by substrate level phosphorylation b. by oxidative phosphorylation

15. Which has the potential of producing the most ATP? a. glucose b. amino acid c. fatty acid