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128 Cards in this Set
- Front
- Back
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adenosine triphosphate (ATP)
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a major source of chemical energy for chemical work.
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bioenergetics:
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the area of thermodynamics that deals specifically with the energetic reactions that occur in an organism
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chemical work:
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non-spontaneous reactions between molecules
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endergonic reaction:
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refers to the change in free energy when energy enters a system
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endothermic reaction
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has a positive delta H and will absorb heat
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energy
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that which can or does move matter (i.e., the capacity for doing work)
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energy coupling:
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the use of an exergonic (energy-releasing) process to drive an endergonic (energy-requiring) process
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enthalpy (H)
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he total energy in a system
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entropy (S)
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disorder
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exergonic reaction:
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refers to the change in free energy when energy leaves a system
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exothermic reaction
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has a negative delta H and will release heat
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free energy (G):
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the energy available (or required) to do work in a given system
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kinetic energy
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refers to energy that is associated with moving matter
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mechanical work:
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work such as contracting muscle cells; the amount of energy transferred by force.
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metabolism:
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all of the chemical reactions that occur in an organism
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non-spontaneous reaction:
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a reaction which has a positive delta G
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potential energy:
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refers to energy that is stored
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spontaneous reaction:
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a reaction which has a negative delta G
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system:
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any collection of matter under thermodynamic scrutiny
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thermodynamics
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the physics of energy transformations that occur in a collection of matter
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transport work:
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transporting substances across a cell membrane
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work
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the act of moving matter
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What is one of the major characteristics of life pertinent to this tutorial?
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One of the major characteristics of a living organism is that it can obtain and process energy.
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hat is metabolism? Review anabolic and catabolic reactions and relate them to metabolism in living organisms.
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Metabolism refers to all of the chemical reactions that occur in an organism. Metabolic reactions can be subdivided into those that result in the formation of molecules (anabolic) versus those that result in the breakdown of molecules (catabolic).
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Name some processes done by living organisms which classify as anabolic reactions. Name some which classify as catabolic reactions.
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During photosynthesis, photoautotrophs (e.g., land plants) convert the energy found in sunlight into chemical energy via a series of anabolic reactions that result in starch being formed and stored within the plant. Chemoheterotrophs (e.g., humans) eat starch and break it down via a series of catabolic reactions to obtain the stored chemical energy.
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What is energy? Name and describe two types of energy. Give examples which compare the two.
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Energy refers to that which can or does move matter (i.e., the capacity for doing work). Let's consider two forms of energy. Kinetic energy refers to energy that is associated with moving matter. Potential energy refers to energy that is stored. The Hoover Dam on the Colorado River (shown here) blocks the normal flow of water and stores potential energy behind its walls. When released, the kinetic energy of the swiftly flowing water is harnessed to provide electricity for 1.3 million people a year. There are many other possible examples.
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Discuss how temperature relates to energy. What is heat? What is cold? What do we actually feel when something is hot or cold?
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The temperature of an object is a reflection of the kinetic energy of its atoms or molecules. Fast molecules = high kinetic energy = high temperature. Boiling water has a much higher temperature (and higher kinetic energy) than ice. Our bodies sense the kinetic energy of the molecules.
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Name some molecules in which humans and other living organism store energy.
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Carbohydrates, fats, proteins (though these are broken down by the body less often).
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Describe what chemical bonds do, and how they are structured. What are the necessary components of a chemical bond? What is the key part of a chemical bond, and also one of the key components of metabolic reactions?
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Chemical bonds hold atoms together and these bonds form as a result of electron behavior (either directly or indirectly). Electrons have mass and hence, their movement requires energy. In addition, electrons contain varying amounts of potential energy. Without electrons, chemical bonds could not exist, nor could many metabolic reactions.
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Does it take energy to create chemical bonds? What about breaking bonds?
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No, energy is released when bonds are formed. However, it takes energy to break chemical bonds.
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Differentiate between a Calorie and a calorie.
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1 Calorie = 1,000 calories, or 1 kcal = 1 Calorie.
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What is the study of thermodynamics? How is it studied in life? What is a system in biological and non-biological terms?
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hermodynamics is the physics of energy transformations that occur in a collection of matter (formally, any collection of matter under thermodynamic scrutiny is defined as a "system"). Bioenergetics is the area of thermodynamics that deals specifically with the energetic reactions that occur in an organism; energetically, an organism is a "system." (FYI: collections of organisms and abiotic components can also be systems, i.e. “ecosystems.”)
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What are the laws of thermodynamics? Explain why energy is actually “converted” instead of made.
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The first law of thermodynamics states that energy is neither created nor destroyed. In other words, the amount of energy in the universe is constant. This first law could be considered "bookkeeping." It states that the energy used and released in any reaction must be balanced. The second law of thermodynamics deals with the ordering of matter, and states that all energy-affected matter in the universe is becoming random. Energy can only be “converted” instead of made because there is only a set about of energy in the universe, as stated by the first law. If the amount of energy in the universe is constant, then creating more energy would change the amount of energy in the universe.
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What is the concept of entropy? Explain how it relates to the second law of thermodynamics.
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The second law of thermodynamics states that all energy-affected matter in the universe is becoming more and more random—in other words, it is increasing in entropy.
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What is required for order? How can everything be moving towards greater randomness, yet life still be very ordered?
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Energy input is required to create order. Systems can become ordered as long as they are "open" to the universe. Life exists as a system that is open to the universe and ultimately, the energy that organisms obtain is used, in a sense, to reverse entropic change.
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Descibe—in thermodynamic terms—why someone can starve to death.
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If you stop eating you will die because there is no input of energy from outside your body (i.e., your system) to reverse the natural tendency of matter to disorder.
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How does entropy change with temperature? Think about the state of matter at different temperatures and the order of that matter.
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The entropic state of a given system is proportional to temperature. At absolute zero (in degrees Kelvin), the entropic state of any system is zero. (Right now, science has not yet been able to achieve a state of zero disorder i.e. 0 degrees Kelvin.)
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What is free energy? How is work done by a system? How is work done on a system?
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Free energy (G) is the energy available (or required) to do work in a given system. If a given system releases free energy, then it can do work. Conversely, if it absorbs free energy, then work can be done on it.
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What are endergonic and exergonic reactions? Is a spontaneous reaction endergonic or exergonic?
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he change in free energy (delta G) is endergonic if energy enters the system, and exergonic if it leaves the system. Moreover, an exergonic reaction is unstable, has a negative delta G and is therefore, a spontaneous reaction.
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Name one very important reason why energy transfer is not 100% efficient?
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Friction exists, and energy can thus be lost to heat.
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How do free energy changes relate to life? Describe briefly, on a molecular level, how energy flows through a living organism. How does a release of free energy usually affect the entropy of a system, and why?
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The free energy changes (delta G) associated with life's metabolic energy involve the movement of matter. This free energy comes from a series of metabolic reactions that result in work being done at the molecular level (i.e., the movement of electrons, atoms, or molecules). Recall the relationship between free energy and stability; a given reaction (i.e., a system) that has the potential to do a lot of work (i.e., release a lot of free energy) is inherently unstable; it typically has a low relative entropy and tends to change spontaneously to a more stable, disordered state.
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What is more likely to release free energy, a system with high entropy or a system with low entropy? Why?
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A system that has the potential release a lot of free energy is inherently unstable; therefore, it typically has a low relative entropy and tends to change spontaneously to a more stable, disordered state. A system with a lower entropy is more likely to release free energy.
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What is the difference between total energy and free energy? What is “total energy” of a system called, and how is it denoted in shorthand?
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Not all of the energy in a system (i.e. total energy) is energy that is available to do work (i.e. free energy). Enthalpy (H) is the total energy in a system.
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What terms are used to describe and measure a change in enthalpy? What reactions are associated with the changes?
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If enthalpy is negative, then some energy (typically heat) will leave the system. If this value is positive, then energy will enter the system (typically heat will be absorbed from outside). An exothermic reaction has a negative delta H and will release heat, whereas an endothermic reaction has a positive delta H and will absorb heat.
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How is a change in entropy expressed? What abbreviations are used?
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The entropic state of the system is denoted S. If the reaction results in an increase in entropy, then this value is positive. If the reaction decreases in entropy, then this value is negative.
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Write out the free energy equation. Describe each term within the free energy equation. By re-ordering the equation, discuss how each value is related or changed by another.
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delta G = delta H - T(delta S)
change in free energy = change in total energy – temperature times change in randomness This equation reveals that not all of the energy stored in a system is available for work; free energy is less than the total energy of a system. The free energy concept can be used to determine whether a specific process or reaction will occur spontaneously. A change in total energy = the change in free energy + the temp * change in randomness Temperature = (change in total energy – change in free energy) / change in randomness A change in randomness = (change in total energy – change in free energy)/ temperature |
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What does a more negative value of ΔG mean in the free energy equation? What does a more positive value mean?
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he more negative the value of delta G, the more free energy released by the reaction, and the more work that can be done. Conversely, as delta G becomes progressively more positive, the energy required for the reaction to proceed also increases.
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What is the major source of stored energy in cells? Describe or draw this molecule, and describe how it stores this energy (i.e. what features of the molecule make it “easy” to release energy”).
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A major source of chemical energy for this work is adenosine triphosphate (ATP). ATP is a 5-carbon sugar (ribose) attached to a nitrogenous base (i.e., adenine; recall our discussion of the nucleotides DNA and RNA) and a group of three phosphates. The three phosphates are the triphosphate component of adenosine triphosphate, and they are very unstable. This instability is due to the three negative charges that induce an intramolecular strain in one area of the molecule. Most reactions that involve ATP depend on the hydrolysis of the third phosphate to liberate the potential energy that can be used to do work.
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Write out the equation for the hydrolysis of ATP. Draw the products of the hydrolysis reaction. How much energy is usually released by the hydrolysis of ATP? Is this a catabolic reaction or an anabolic reaction? An exergonic or endergonic reaction?
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The hydrolysis of ATP is an exergonic reaction (which is a catabolic reaction). The hydrolysis of ATP releases 7.3 kilocalories per mole.
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What is energy coupling and why is ATP an integral part of energy coupling in living organisms? Can you think of any examples of energy coupling in other systems (even non-living ones)?
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The use of an exergonic (energy-releasing) process to drive an endergonic (energy-requiring) process is called energy coupling. In many living organisms, ATP undergoes hydrolysis (an exergonic reaction) to create enough energy to drive endergonic reactions, such as protein building. There are many examples of energy-coupled systems, including gasoline-fueled vehicles, etc.
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What are the three main types of work cells do? How is ATP involved?
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A cell does three types of work: mechanical (e.g., contracting muscle cells), transport (e.g., moving substances across the cell membrane), and chemical (e.g., non-spontaneous reactions between molecules; discussed in the next section). A major source of chemical energy for this work is adenosine triphosphate (ATP), which fuels this work in a energy coupling process.
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alcohol fermentation:
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pyruvate gives off carbon dioxide and is converted to ethyl alcohol (ethanol) in a two-step process
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cellular respiration
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a catabolic pathway comprised of a series of steps that convert the chemical energy in glucose into the energy contained in ATP
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electronegativity:
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the affinity for electrons
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fermentation:
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the process by which glucose is partially broken down and NAD+ is regenerated
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glycolysis:
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a ten-step process which involves the initial breakdown of glucose to pyruvate (or pyruvic acid), water, and reduced electron carriers (in this case, NADH), and from which ATP is produced.
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lactic acid fermentation:
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process by which pyruvate is converted to lactate (lactic acid)
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NAD+
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nicotinamide adenine dinucleotide in its oxidized form
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NADH:
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nicotinamide adenine dinucleotide in its reduced form
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oxidation:
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a loss of electrons
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oxidized:
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describes a molecule that loses an electron
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pyruvate:
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one of the products of the initial breakdown of glucose
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redox :
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short for the chemical process known as "reduction-oxidation,” and refers to the transfer of electrons that occurs during many chemical reactions.
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reduced:
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describes a molecule that gains an electron and thus has a "reduction" in its positive charge
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reduction:http://www.flashcardexchange.com/mycards/add/915026
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a gain in electrons
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substrate-level phosphorylation:
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part of glycolysis in a phosphorylated molecule (e.g., the substrate PEP in the figure below) transfers a phosphate group to ADP
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Review the basics of cellular respiration. What types of molecules broken down in cellular respiration? What is the end product of cellular respiration?
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Cellular respiration is a catabolic pathway comprised of a series of steps that convert the chemical energy in glucose into the energy contained in ATP. Molecules can enter the pathway at various points; therefore, glucose is just one of several sugars that can be broken down during cellular respiration. The end product of cellular respiration is ATP.
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What does it mean when something is oxidized? When it is reduced?
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A molecule that gains an electron is reduced, meaning that there has been a "reduction" in its positive charge. This gain in electrons is termed reduction. A molecule that loses an electron is oxidized, and this loss of electrons from a molecule is termed oxidation.
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What is a “redox” reaction? How do these reactions release or store energy? Describe how a “redox” reaction is an example of energy coupling.
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The term “redox" is short for the chemical process known as "reduction-oxidation." It refers to the transfer of electrons that occurs during many chemical reactions. During cellular respiration, there is a relocation of electrons, and this relocation results in the release of energy that is stored in food molecules. Released energy is used to synthesize ATP. Energy is coupled when the relocation of electrons releases energy, and that energy is used to synthesize ATP.
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Write the general form of a “redox” reaction. Explain the “shorthand” used in this notation.
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Xe- + Y -→ X + Ye-
In this equation, molecule "X" is oxidized and loses an electron (and energy); molecule "Y" is reduced and gains an electron (and energy). |
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Review the concept of electronegativity. Is an electronegative atom/molecule more likely to gain or lose electrons?
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Review the concept of electronegativity. Is an electronegative atom/molecule more likely to gain or lose electrons?
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What is a calorie? Is the number of calories produced by one “round” of cellular respiration constant or variable?
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A calorie is defined as the amount of energy that will raise 1 gm of water by 1 deg C. The oxidation of 1 mole of glucose releases 686,000 calories (686 Calories). Generally constant, since one glucose molecule can only produce a certain amount of energy.
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Describe cellular respiration in terms of electronegativity, energy transfer, and redox reactions.
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Cellular respiration is a series of reactions in which electrons are sequentially moved from glucose (and its catabolic products) to oxygen (or, in some cases, to an alternative terminal electron acceptor). Oxygen is highly electronegative; it tends to pull electrons towards itself and away from other molecules, so that glucose is oxidized and oxygen is reduced. Consequently, it takes energy to keep electrons away from oxygen. As the electrons move closer to oxygen, they lose energy and the energy that is released can be used to do work. Restated, cellular respiration is a series of redox reactions in which energy is gradually made available to do work.
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What is commonly used as an electron acceptor during respiration?
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Oxygen.
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What is the general equation for cellular respiration? What are the reactants and the end products (in general terms, not formulas)?
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C6H12O6+ 6 O2 -→ 6 CO2 + 6 H2O + energy
Glucose and oxygen = reactants Carbon dioxide, water, and energy = products |
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How does the cell control the reaction so that the energy can be useful and not lost as heat?
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The cell controls the cellular respiration reaction by completing it in a series of steps instead of one large step. A high amount of energy is released from the oxidation of glucose, and unless the body controlled this oxidation much of this energy would be wasted as heat. The cell gradually oxidizes glucose in a series of controlled steps and electrons (and accompanying energy) are gradually released.
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What are NAD+ and NADH? What part to they play in cellular respiration?
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The most prevalent electron carrier in cellular respiration is nicotinamide adenine dinucleotide. This electron carrier can exist in its reduced form (NADH) or as an oxidized positive ion (NAD+). NAD+ is free to pick up electrons, whereas NADH has two more electrons and an additional proton.
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Draw the structure for NAD+ and NADH. What type of reaction occurs to convert one to the other?
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Redox reactions occur to convert NAD+ to NADH, and vice versa. To convert NAD+ to NADH, a reduction reaction occurs. To do the opposite, an oxidation reaction occurs.
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What is an oxidizing agent? What is an oxidizing agent in redox reactions, and what part does it play? How does it relate to oxidation?
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A molecule that loses an electron is oxidized, and this loss of electrons from a molecule is termed oxidation. NAD+ functions as an oxidizing agent (electron acceptor) during cellular respiration, picking up electrons from the catabolic products of glucose (along with hydrogen atoms). Each NAD+ molecule can be reduced with two high-energy electrons and one hydrogen atom. Importantly, once the transfer is complete and the reduced NADH has deposited its electrons (oxidation), the regenerated NAD+ can pick up more electrons and begin again.
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In terms of thermodynamics, what happens to unstable, high-energy molecules?
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High-energy molecules are unstable and can spontaneously change into low-energy molecules, accompanied by a release of energy that can do work.
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What are the three metabolic stages of cellular respiration and give a brief overview of what happens in the first stage. Do all these processes occur in both eukaryotes and prokaryotes?
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Respiration can be broken down into three metabolic stages:
1. Glycolysis: involves the initial breakdown of glucose to pyruvate (or pyruvic acid), water, and reduced electron carriers (in this case, NADH). 2. The Krebs cycle 3. Electron transport and oxidative phosphorylation Yes, the processes of cellular respiration occur in both eukaryotes and prokaryotes. |
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Where does each stage of cellular respiration take place?
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Glycolysis occurs in the cytosol, whereas the Krebs cycle and electron transport occur in the mitochondria.
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Is glucose the only sugar used in the body? How does the body use these other sugars?
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No. Other sugars are either converted to glucose or introduced at other points in the glycolytic pathway.
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Is glucose the only energy source used in the body? What are others and how does the body use them?
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No. In addition to the other sugars, the body can use proteins and fats for energy. These foods are catabolized and the metabolic breakdown products enter the cellular respiratory pathway at various points.
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What initiates the process of glycolysis? How are the bonds in glucose broken to produce energy?
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Glycolysis is initiated by the addition of a phosphate (P), from ATP, to a molecule of glucose; this destabilizes the glucose molecule and the bonds are then easily broken to release energy.
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How many steps are involved in glycolysis? What occurs during these steps that actually make ATP? What is needed to complete this?
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Glycolysis is a ten-step process. At two steps, a phosphorylated molecule transfers a phosphate group to ADP. It takes two molecules of ATP to break down one molecule of glucose to pyruvate. The output is four ATPs and two NADHs. Therefore, there is a net gain of two ATPs and two NADHs from one molecule of glucose from glycolysis alone. Most of the energy remains in the pyruvate molecule.
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How much ATP is used? How much is gained? What is the net change in ATP and in NAD+?
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The initial "investment" of energy in the early stages, which require 2 ATP molecules per molecule of glucose. In the later stages, 4 ATP molecules and 2 NADH molecules are produced, which yields a net production of 2 molecules of pyruvate, 2 molecules of ATP, and 2 molecules of NADH per molecule of glucose.
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What happens to pyruvate after glycolysis? Where can it go and what can occur?
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Pyruvate is further modified and enters the next stages of cellular respiration (i.e., the Krebs cycle and the electron transport chain). It is at these stages that most of the ATP is produced for cellular work.
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What is fermentation? Why would organisms use this process instead of cellular respiration?
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The process by which glucose is partially broken down and NAD+ is regenerated is fermentation. The many types of fermentation differ in the waste products that are formed when pyruvate is broken down. Fermentation can occur in the presence or absence of oxygen. If organisms are living in an anaerobic environment, then fermentation is the only way in which they can undergo cellular respiration.
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What is necessary for cellular respiration but not necessary for fermentation?
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Oxygen.
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What are two common forms of fermentation? Describe each.
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Two common types of fermentation are alcohol fermentation and lactic acid fermentation. In alcohol fermentation, pyruvate gives off carbon dioxide and is converted to ethyl alcohol (ethanol) in a two-step process. In lactic acid fermentation, pyruvate is converted to lactate (lactic acid). The figure below depicts both types.
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ATP synthase:
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the protein complex in the presence of which chemiosmosis is accomplished
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charge differential (voltage):
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created by the movement of protons across the inner mitrochondrial membrane (by the electron transport chain), it is the difference in proton concentration (i.e. “charge”) across the membrane
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chemiosmosis
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the process in which excess protons from the intermembrane space flow back into the mitochondrial matrix and ADP is phosphorylated to make ATP.
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electron transport chain:
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collectively refers to a set of membrane-bound enzymes which provide the energy to do work by moving positively charged hydrogen atoms
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FAD, FADH2
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like NAD+/NADH, these are electron carriers
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homeotherm:
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"warm-blooded" animals which use the “waste” product of cellular respiration, heat, to maintain a constant body temperature.
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Krebs cycle:
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part of cellular respiration in which electrons are removed from acetyl CoA and reduce more NAD+ and FAD.
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mitochondrial matrix:
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the part of the mitochondrion enclosed within the inner membrane, which houses the enzymes and substrates for the Krebs cycle
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mitochondrion
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contains the membrane-bound enzymes which comprise the electron transport chain.
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oxidative phosphorylation:
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the generation of ATP from chemiosmosis
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proton:
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positively charged hydrogen atoms (H+)
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terminal electron acceptor:
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the last electron acceptor in the electron transport chain. This acceptor must be extremely electronegative; oxygen often is the terminal electron acceptor in the ETC.
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In a few words, describe what happens during glycolysis. How much energy in the form of ATP and NADH is produced and what product goes on to the final steps of cellular respiration?
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At the end of glycolysis, there is a net production of two molecules of ATP and two molecules of NADH. The ATP is produced via substrate-level phosphorylation; in this reaction, a phosphate group on an organic molecule is transferred directly (along with high-energy electrons) onto a molecule of ADP. Pyruvate is the end product which goes on to the final steps of cellular respiration.
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How much energy does each new molecule of ATP gain at the end of glycolysis? How much does NADH gain?
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At the end of glycolysis, there is an effective transfer of 20 kcals of energy to ATP (about 10 kcals each) and about 80 kcals of energy to NADH (about 40 kcal each).
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How much energy is gained by glycolysis alone? How much energy can be harvested from glucose? At the end of glycolysis, how much energy would then remain in each pyruvate molecule?
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At the end of glycolysis, 100 kcals of energy is gained. However, the complete oxidation of glucose results in the release of 686 kcals of energy; therefore, there is a good deal of energy still remaining in pyruvate (about 584 kcals!).
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Where is pyruvate transferred to? What is the final form that pyruvate is converted into? What is the name of the cycle to which this final product is subjected?
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In eukaryotes, pyruvate is transported across the mitochondrial membrane and then converted to acetyl CoA (with the production of NADH and carbon dioxide). The Krebs cycle uses acetyl CoA to couple more energy.
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What are the net energetic products and number of reduced electron carriers of one round of the Krebs cycle? For one molecule of glucose, how many rounds of the Krebs cycle will occur?
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1 ATP, 3 NADH, and 1 FADH2
Because each molecule of glucose produces two pyruvate molecules, the Krebs cycle occurs twice for each molecule of glucose. |
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Acetyl CoA enters a series of enzymatic reactions during the Krebs cycle. Why do you think that this set of reactions is known as a cycle?
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This pathway is termed a "cycle" (and diagrammed as a circle) because the end product becomes the first product after reacting with acetyl CoA.
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What happens during the Krebs cycle to the acetyl CoA?
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During the Krebs cycle, there is complete oxidation of acetyl CoA. At the end of the cycle, CoA is converted into CoA—SH.
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What electron carriers are used during this cycle? What do they reduce to?
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NAD+ à NADH
FAD à FADH2 |
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What happens to the NADH and FADH2 molecules that are formed?
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The high energy electrons contained within these molecules will passed down to the electron transport chain, the final step of cellular respiration.
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What is the (not energetically useful) byproduct released during the Krebs cycle?
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Carbon dioxide.
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What are the main reactants of the Krebs cycle?
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Acetyl CoA, NAD+, FAD, ADP, and inorganic phosphate.
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What are all of the main products?
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Carbon dioxide, NADH, FADH2, and ATP
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Aside from the ATP produced directly, where is a majority of the energy stored after the Krebs cycle?
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Because only one additional ATP molecule (per molecule of pyruvate) is produced by substrate-level phosphorylation in the Krebs cycle, the majority of the energy is tied up in NADH and FADH2.
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Where will these energetically useful products of the Krebs cycle be used? What will they be converted into?
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The high-energy electrons within NADH and FADH2 will be passed to a set of membrane-bound enzymes in the mitochondrion that are collectively referred to as the electron transport chain. They will be converted into useful energy.
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Briefly, how is ATP synthesized from the two electron transporters?
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The electron transporters will move electrons so that the electrons provide the energy to move positively charged hydrogen atoms (H+), also known as protons. The movement of protons across the inner mitrochondrial membrane (by the electron transport chain) creates a charge differential (i.e., voltage) that will be used to synthesize ATP.
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What type of molecules make up the electron transport chain? Why are the electronegativities of molecules within the electron transport chain important, and how do the electronegativities create a chain?
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The ETC is composed of a number of molecules (mostly proteins) that are located in the inner membrane of the mitochondrion. Each membrane protein has a particular electronegativity (affinity for electrons). The more electronegative the molecule, the more energy required to keep the electron away from it. In this way, a slightly electronegative membrane protein will pull electrons away from reduced electron carriers. In the presence of an even more electronegative molecule, these electrons will be oxidized from the first membrane protein, and so on, thus creating a chain.
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What is usually the final electron acceptor in the chain? What is special about this molecule? How does using this final electron acceptor create a maximal amount of free energy?
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Oxygen is usually the final electron acceptor in the ETC, due to its very high electronegativity. When oxygen acts as the terminal electron acceptor, there is a maximal amount of free energy released and hence, more protons can be transported (which means that a greater charge buildup occurs across the inner mitochondria membrane).
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What happens to this final acceptor? How is it disposed?
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Oxygen is reduced by electrons, then picks up hydrogen ions to form water. Water is disposed of as a waste product.
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Specifically, how is energy made available in the ETC?
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An electron from one protein is transferred to another in the chain, so that each step has a negative ΔG. Therefore, with each oxidation/reduction reaction in every step of the ETC, energy is made available to do work. That work involves the movement of protons. This creates a charge differential (voltage) across the inner membrane; it is this stored energy that is actually used to synthesize ATP.
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What work is this energy used for? What does it set up?
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This energy is used for chemiosmosis of ATP. During the movement of electrons through the electron transport chain, protons accumulate on the inside of the inner mitochondrial membrane. As electrons move from one member of the electron transport chain to the next, protons are transported from one side of the membrane to the other, resulting in a buildup of protons in the intermembrane space. This sets up a voltage gradient which is later used for phosphorylation of ATP.
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What does the ETC create across the mitochondrial membrane? How does this synthesize ATP?
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The ETC creates a voltage gradient, i.e. a different concentration of protons, across the mitochondrial membrane. As these excess protons from the intermembrane space flow back into the mitochondrial matrix (the part of the mitochondrion enclosed within the inner membrane, which houses the enzymes and substrates for the Krebs cycle), ADP is phosphorylated to make ATP (chemiosmosis). Chemiosmosis is accomplished in the presence of the protein complex ATP synthase, which is also located in the inner mitochondrial membrane.
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How does the movement of protons fuel the phosphorylation of ADP? How is the energy converted? What enzyme is involved?
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Transfer of electrons provides the energy to move protons across the inner mitochondrial membrane. This buildup of protons creates a charge differential (voltage), and this stored energy is then used to provide energy to the ATP synthase (the important enzyme) complex to affect the production of ATP.
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Review substrate level phosphorylation. How is it different then the way ATP is generated in the mitochondria by the ETC?
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Review substrate level phosphorylation. How is it different then the way ATP is generated in the mitochondria by the ETC?
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What is an estimated yield of ATP per molecule glucose? How might energy be lost during cellular respiration?
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The estimated maximum net yield of one molecule of glucose is 38 ATP. Much of the energy bound in a molecule of glucose is actually lost as heat during metabolism.
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If an organism relied only on glycolysis and fermentation, what would be the net amount of ATP generated? Compare this to glycolysis with respiration. Can you think of some examples in which human bodies rely on glycolysis and fermentation instead of glycolysis and respiration?
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Fermentation and cellular respiration are anaerobic and aerobic alternatives, respectively, for producing ATP by harvesting the chemical energy from food. Both pathways use glycolysis, which produces a net 2 ATP by substrate phosphorylation. Without oxygen, the energy stored in pyruvate is unavailable to the cell, but with oxygen, pyruvate can be further broken down to yield many more ATP. Glycolysis + respiration yields about 38 ATP, whereas glycolysis + fermentation only yields about 2 ATP.
Human muscle cells can switch from glycolysis + respiration to glycloysis + fermentation, when we exercise and there’s not enough oxygen “to go around.” The lactate that is produced as a byproduct of the lactic acid fermentation in muscle cells can cause muscle fatigue and pain, but is eventually carried to the liver. |
