Chm130in Capstone Project: Cellular RespirationJones Willyce

Chm130in Capstone Project Cellular Respiration Jones Willycellular

Review chapter 22 in your chemistry text. The cells of our bodies require a continuous supply of energy just to stay alive. The direct source of that energy is a molecule called adenosine triphosphate (ATP). This molecule is essentially a nucleotide (the nitrogenous base adenine, a ribose sugar, and a phosphate group) with two extra phosphate groups attached. The phosphate groups are negatively charged, creating a repulsion that creates potential energy stored in ATP. When a phosphate group is transferred to another molecule from ATP (like to a reactant in a reaction), energy can be used to move a muscle cell or transport proteins in a cell membrane.

This transfer of the phosphate group is how energy can be utilized for cellular activities. This process converts ATP into ADP (adenosine diphosphate), which can later be reconverted back into ATP for repeated use.

Question 1: Is the release of a phosphate from ATP to form ADP an endothermic or an exothermic reaction? Explain.

Answer: The release of a phosphate from ATP to form ADP is an exothermic reaction. This is because breaking the high-energy phosphate bond releases energy, making the process energetically favorable and releasing heat. The hydrolysis of ATP releases energy that the cell can harness for various functions, which characterizes it as an exothermic process.

Question 2: Is the conversion of ADP back into ATP an endothermic or an exothermic reaction? Explain.

Answer: The conversion of ADP back into ATP is an endothermic process. It requires an input of energy, typically derived from the oxidation of nutrients during cellular respiration, to add a phosphate group to ADP to regenerate ATP. This process consumes energy, characteristic of endothermic reactions.

Question 3: How is energy stored in ATP? Because of our constant need for ATP, much of our daily efforts to stay alive are related to eating food, which supplies the energy needed to convert ADP back into high-energy ATP. We refer to this process as “cellular respiration” because we take in oxygen and oxidize our food to supply this energy. Our digestive system hydrolyzes carbohydrates into glucose, which can be transported by the circulatory system and carried directly into cells. The reactions of cellular respiration involving glucose are very complex, but the overall reaction is a simple one that looks like this: C₆H₁₂O₆ + O₂ → CO₂ + H₂O + 38 ATP

Balance the above equation. (Ignore the ATP for now.)

Balanced equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Question 4: Which reactant in this reaction is oxidized, and which reactant is reduced? Explain.

Answer: Glucose (C₆H₁₂O₆) is oxidized, and oxygen (O₂) is reduced. Oxidation involves the loss of electrons, which occurs when glucose loses electrons during its breakdown to produce CO₂. Reduction involves gaining electrons, which occurs when oxygen accepts electrons to form water.

Question 5: Is the breakdown of glucose endothermic or exothermic? Explain.

Answer: The breakdown of glucose in cellular respiration is an exothermic process. It releases energy as glucose is oxidized to produce CO₂ and H₂O, providing energy for ATP synthesis.

Question 6: The body can absorb up to 120 grams of carbohydrate per hour from the small intestine. If we assume this is all in the form of glucose, how many moles of glucose have been absorbed?

Answer: Moles of glucose = mass / molar mass.

Molar mass of glucose = 180 g/mol.

Moles = 120 g / 180 g/mol ≈ 0.667 mol.

Question 7: If all of the 120g of glucose are converted within muscle cells to energy (ATP), how many grams of H₂O will be produced? How many grams of CO₂ will be produced?

Answer:

From the balanced equation, 1 mol glucose produces 6 mol CO₂ and 6 mol H₂O.

Number of moles of glucose = 0.667 mol.

CO₂ produced = 0.667 mol × 6 = 4 mol.

H₂O produced = 0.667 mol × 6 = 4 mol.

Mass of CO₂ = 4 mol × 44 g/mol = 176 g.

Mass of H₂O = 4 mol × 18 g/mol = 72 g.

Question 8: Explain where the metabolic reactions take place in the cell based on Figure 22.2 p 785.

Answer: Metabolic reactions of cellular respiration occur primarily in the mitochondria, often called the “powerhouses” of the cell. Glycolysis occurs in the cytoplasm, while the citric acid cycle and electron transport chain are localized within the mitochondrial matrix and inner mitochondrial membrane, respectively.

Question 9: Describe the components and functions of FAD, NAD⁺.

Answer: NAD⁺ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) are essential coenzymes in cellular respiration. NAD⁺ accepts electrons and is reduced to NADH during glycolysis and the citric acid cycle. FAD similarly accepts electrons and becomes FADH₂. These molecules function as electron carriers, shuttling electrons to the electron transport chain for ATP production.

Question 10: When NADH and FADH₂ transfer their electrons to molecules in the electron transport chain, are they reduced or oxidized? Explain.

Answer: NADH and FADH₂ are oxidized when they transfer their electrons to the electron transport chain. They lose electrons and are thus converted back to NAD⁺ and FAD, respectively.

Question 11: How does the electronegativity of an oxygen atom compare to the electronegativity of the other molecules in the electron transport chain?

Answer: Oxygen has a higher electronegativity (3.44 on the Pauling scale) compared to other molecules in the electron transport chain. This high electronegativity allows oxygen to effectively accept electrons at the end of the chain, forming water.

Question 12: Why is oxygen so important in the process of cellular respiration? What will happen if the body does not receive enough oxygen?

Answer: Oxygen is essential as the final electron acceptor in the electron transport chain, enabling continuous electron flow and ATP production. Without adequate oxygen, electron transport halts, causing a backup of electrons, cessation of ATP synthesis, and leading to anaerobic conditions, which produce less ATP and can result in lactic acid buildup.

Question 13: How do cyanide and carbon monoxide affect the electron transport chain when the body is exposed to either of these toxins?

Answer: Cyanide and carbon monoxide inhibit cytochrome c oxidase in the electron transport chain. Cyanide binds tightly to the iron in cytochrome c oxidase, preventing electron transfer to oxygen, effectively halting ATP production. Carbon monoxide also binds to the same site, disrupting cellular respiration and leading to cellular suffocation and death if exposure is severe.

Question 14: Summarize the diagram about ATP energy and Ca²⁺ needed to contract muscles, and explain the role of muscle fibers in this process.

Answer: The diagram illustrates how ATP provides the energy necessary for muscle contraction by powering the myosin heads in muscle fibers. Calcium ions (Ca²⁺) regulate this process by binding to troponin, causing conformational changes that allow myosin to bind to actin. The hydrolysis of ATP energizes the myosin heads, enabling them to pivot and pull actin filaments, resulting in muscle contraction. Adequate ATP and Ca²⁺ are essential for continuous and controlled muscle movements.

References

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