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25 Cards in this Set
- Front
- Back
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reduction:
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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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The affinity for electrons is termed electronegativity. The more electronegative a molecule is, the more likely it will become reduced by the addition of electrons in a chemical reaction. Therefore, an electronegative molecule is more likely to gain 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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n 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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here 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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