Download chapter 11 BIOCHEMISTRY and more Exercises Biochemistry in PDF only on Docsity!
Question 1 A 65-year-old patient is undergoing metabolic assessment, and his physician notes that his basal metabolic rate has significantly decreased. Based on biochemical thermodynamics, which hormone is primarily responsible for maintaining metabolic rate, and how does it affect energy balance? A) Insulin – Increases metabolic rate by promoting glucose uptake B) Thyroid hormone – Increases metabolic rate by enhancing mitochondrial activity C) Glucagon – Lowers metabolic rate by promoting gluconeogenesis D) Growth hormone – Directly increases metabolic rate through protein synthesis Correct Answer: B) Thyroid hormone – Increases metabolic rate by enhancing mitochondrial activity Explanation: Thyroid hormones (T3 and T4) play a crucial role in regulating basal metabolic rate (BMR). They enhance mitochondrial function by increasing oxygen consumption and ATP production, which is why a deficiency in thyroid hormones leads to a lower metabolic rate, fatigue, and weight gain. T3 is the more biologically active form, while T4 acts as a prohormone that gets converted to T3. These hormones stimulate enzymes involved in oxidative phosphorylation, thus increasing ATP synthesis and heat production. A deficiency, as seen in hypothyroidism, results in decreased BMR, whereas hyperthyroidism leads to an excessive metabolic rate. Reasons for Incorrect Answers: A) Insulin – Insulin primarily regulates glucose metabolism but does not directly increase BMR. It promotes glucose uptake and storage rather than increasing mitochondrial activity. C) Glucagon – While glucagon promotes gluconeogenesis and glycogen breakdown, it does not significantly regulate BMR. Instead, it maintains blood glucose levels during fasting. D) Growth hormone – Growth hormone (GH) promotes protein synthesis and muscle growth but does not directly regulate basal metabolism the way thyroid hormones do. Question 2 A biochemist is designing an experiment on the thermodynamic principles of metabolic reactions. According to the first law of thermodynamics, which of the following statements is correct regarding energy transformations in biological systems? A) Energy can be created when necessary to drive metabolic reactions B) Energy can be transformed from one form to another but cannot be created or destroyed C) Living systems can store excess energy indefinitely without dissipation D) Energy is completely lost when converted into heat during metabolism
Correct Answer: B) Energy can be transformed from one form to another but cannot be created or destroyed Explanation: The first law of thermodynamics, also known as the law of conservation of energy , states that energy cannot be created or destroyed but can only change from one form to another. In biological systems, energy from food is converted into ATP, which is then used for cellular processes. Some energy is always lost as heat, which contributes to body temperature regulation. Reasons for Incorrect Answers: A) Energy can be created when necessary to drive metabolic reactions – This contradicts the first law of thermodynamics. Energy cannot be created; it must come from an external source, such as food. C) Living systems can store excess energy indefinitely without dissipation – Excess energy is often stored as fat, but no system is perfectly efficient. Some energy is always lost as heat. D) Energy is completely lost when converted into heat during metabolism – Heat is a byproduct of metabolism but is not entirely "lost." It is used for thermoregulation in warm-blooded animals. Question 3 During starvation, a patient’s body undergoes metabolic adaptations to maintain homeostasis. What biochemical process is most significantly upregulated in response to starvation? A) Glycolysis B) Lipolysis C) Glycogenesis D) Protein synthesis Correct Answer: B) Lipolysis Explanation: During starvation, the body prioritizes energy production from stored fat through lipolysis : Lipolysis breaks down triglycerides in adipose tissue into glycerol and free fatty acids (FFAs). FFAs are used in β-oxidation to produce ATP. The glycerol can be used in gluconeogenesis to provide glucose to tissues that require it (e.g., the brain and red blood cells). Reasons for Incorrect Answers:
C) A decrease in entropy indicates an exergonic reaction D) Entropy remains constant regardless of metabolic processes Correct Answer: B) Entropy measures the randomness or disorder in a system and increases in spontaneous reactions Explanation: The second law of thermodynamics states that for a process to be spontaneous , the total entropy (disorder) of the system and surroundings must increase. In metabolism, large macromolecules break down into smaller molecules , increasing disorder. Cellular respiration (e.g., glucose → CO₂ + H₂O) releases energy and increases entropy. Reasons for Incorrect Answers: A) Entropy must always decrease for a reaction to proceed spontaneously – This is incorrect because spontaneous reactions increase entropy. C) A decrease in entropy indicates an exergonic reaction – Exergonic reactions release energy, but they do not necessarily decrease entropy. Many break down complex molecules, increasing entropy. D) Entropy remains constant regardless of metabolic processes – This contradicts the second law, as entropy always increases in natural processes. Question 6 A patient presents with a deficiency of ATP production due to mitochondrial dysfunction. Which of the following biochemical consequences would you expect? A) Increased cellular energy availability B) Decreased activity of energy-dependent processes such as active transport C) Unaffected protein synthesis rates D) Enhanced production of metabolic heat Correct Answer: B) Decreased activity of energy-dependent processes such as active transport Explanation: ATP is the primary energy carrier in cells. If mitochondrial function is impaired: Active transport (e.g., Na⁺/K⁺ ATPase pump) slows down, leading to cellular ion imbalances and affecting nerve and muscle function. Protein synthesis and DNA replication are energy-dependent and are reduced under ATP deficiency. Glycolysis and anaerobic pathways may partially compensate, but they produce much less ATP compared to oxidative phosphorylation. Reasons for Incorrect Answers:
A) Increased cellular energy availability – If ATP production is impaired, energy availability decreases , not increases. C) Unaffected protein synthesis rates – Protein synthesis requires ATP. If ATP production is compromised, protein synthesis is reduced. D) Enhanced production of metabolic heat – Mitochondrial dysfunction reduces metabolic efficiency and heat generation, not increases it. Question 7 A biochemical pathway is being studied, and it is noted that one reaction requires an input of energy. How is this reaction classified? A) Exergonic B) Endergonic C) Catabolic D) Spontaneous Correct Answer: B) Endergonic Explanation: Endergonic reactions require energy input and do not occur spontaneously. These reactions often involve biosynthesis (e.g., protein or DNA synthesis). They are coupled to exergonic reactions , such as ATP hydrolysis, to proceed. Reasons for Incorrect Answers: A) Exergonic – Exergonic reactions release energy and occur spontaneously , which is the opposite of endergonic reactions. C) Catabolic – Catabolic reactions break down molecules and release energy (e.g., glycolysis, beta-oxidation), whereas endergonic reactions involve building molecules. D) Spontaneous – Endergonic reactions are not spontaneous; they require an external energy source to proceed. Question 8 During glycolysis, ATP is produced by substrate-level phosphorylation. Which of the following statements best describes this process? A) ATP is generated through electron transport and oxidative phosphorylation B) ATP is directly synthesized by transferring a phosphate group from a high-energy substrate to ADP C) ATP production occurs only in mitochondria D) ATP synthesis in this manner requires the presence of oxygen
C) ΔG is zero, meaning the system is at equilibrium – When ΔG = 0, the reaction is at equilibrium and no net change occurs. Exergonic reactions, by contrast, drive processes forward. D) The reaction requires constant energy input to proceed – This describes an endergonic reaction, not an exergonic one. Question 10 Which of the following best describes the relationship between exergonic and endergonic reactions in biological systems? A) Exergonic reactions directly fuel endergonic reactions B) Endergonic reactions occur spontaneously without requiring energy C) Exergonic reactions require an input of energy to proceed D) Exergonic and endergonic reactions function independently in metabolism Correct Answer: A) Exergonic reactions directly fuel endergonic reactions Explanation: Energy coupling is a fundamental concept in metabolism where exergonic reactions provide the energy needed for endergonic reactions. Example: ATP hydrolysis (exergonic) drives protein synthesis (endergonic). Without coupling, energy-requiring processes would not proceed efficiently. Reasons for Incorrect Answers: B) Endergonic reactions occur spontaneously without requiring energy – This is incorrect because endergonic reactions need an energy input to proceed. C) Exergonic reactions require an input of energy to proceed – Exergonic reactions release energy rather than requiring it. D) Exergonic and endergonic reactions function independently in metabolism – In biological systems, these reactions are coupled to optimize energy use and drive essential processes. Summary of Concepts Covered in Questions 6-10: ATP production and mitochondrial dysfunction impact energy-dependent processes. Endergonic reactions require energy, while exergonic reactions release it. Substrate-level phosphorylation is an oxygen-independent ATP generation method. Negative ΔG defines an exergonic reaction, indicating spontaneity. Metabolic reactions are coupled to maintain energy efficiency in biological systems.
Question 11 A scientist is studying how metabolic pathways regulate energy balance in the body. Which of the following best describes the role of catabolic pathways in metabolism? A) They build up complex molecules from simpler ones B) They require ATP input to proceed C) They break down complex molecules and release energy D) They only occur under conditions of starvation Correct Answer: C) They break down complex molecules and release energy Explanation: Catabolic reactions involve the breakdown of complex molecules (e.g., carbohydrates, lipids, proteins) into simpler forms, releasing free energy in the process. Example: Glycolysis, beta-oxidation, and the citric acid cycle generate ATP by breaking down glucose and fatty acids. Reasons for Incorrect Answers: A) They build up complex molecules from simpler ones – This describes anabolic pathways, which require energy input (e.g., protein synthesis, DNA replication). B) They require ATP input to proceed – Catabolic pathways generate ATP , whereas anabolic pathways require ATP. D) They only occur under conditions of starvation – Catabolic pathways occur continuously to maintain energy levels, not just during starvation. Question 12 A patient has a metabolic disorder that impairs the ability to synthesize new proteins. Which type of metabolic process is most affected in this patient? A) Catabolic processes B) Anabolic processes C) Exergonic processes D) Glycolytic processes Correct Answer: B) Anabolic processes Explanation: Anabolic pathways build complex molecules (e.g., protein synthesis, DNA replication) and require energy input (ATP). If protein synthesis is impaired, cell growth, repair, and function are compromised. Reasons for Incorrect Answers:
Correct Answer: B) It provides immediate energy for cellular reactions by undergoing hydrolysis Explanation: ATP acts as an energy currency by storing and transferring energy in cells. ATP hydrolysis (ATP → ADP + Pi) releases free energy , which is used to power biological processes such as active transport, muscle contraction, and biosynthesis. Reasons for Incorrect Answers: A) It serves as an energy reservoir that can store unlimited amounts of energy – ATP is a short- term energy carrier , not a long-term energy storage molecule (fat and glycogen serve that function). C) It is produced exclusively in the mitochondria via oxidative phosphorylation – ATP is also produced in glycolysis (cytoplasm) and substrate-level phosphorylation. D) It is the final product of anabolic reactions – ATP is used in anabolic reactions but is not a product of them. Question 15 Which of the following statements correctly describes the second law of thermodynamics in the context of biological systems? A) Energy transformations always occur with a decrease in entropy B) Total entropy must increase for a process to be spontaneous C) Biological reactions do not follow the second law of thermodynamics D) The entropy of a system is always constant, regardless of energy flow Correct Answer: B) Total entropy must increase for a process to be spontaneous Explanation: The second law of thermodynamics states that entropy ( disorder or randomness ) must increase for a reaction to be spontaneous. In biological systems, energy transformations (e.g., food digestion, respiration) increase entropy. Reasons for Incorrect Answers: A) Energy transformations always occur with a decrease in entropy – This is incorrect because entropy increases , not decreases, in natural processes. C) Biological reactions do not follow the second law of thermodynamics – Biological systems do follow thermodynamic laws, even though they maintain order at a local level by increasing overall entropy.
D) The entropy of a system is always constant, regardless of energy flow – Entropy is not constant ; it increases in spontaneous processes. Summary of Concepts Covered in Questions 11-15: Catabolic reactions break down molecules and provide energy for anabolic reactions. Anabolic processes build complex molecules and require ATP input. ATP is an energy carrier used in immediate cellular processes. The second law of thermodynamics dictates that entropy must increase in spontaneous reactions. Catabolism and anabolism are interconnected, forming a balanced metabolic cycle. Question 16 A scientist is investigating energy flow in biological systems. He finds that energy transfer is not 100% efficient, and some energy is always lost as heat. Which thermodynamic principle explains this phenomenon? A) The first law of thermodynamics B) The second law of thermodynamics C) Gibbs free energy equation D) The law of conservation of mass Correct Answer: B) The second law of thermodynamics Explanation: The second law of thermodynamics states that in any energy transformation, some energy is always lost as heat , increasing the entropy (disorder) of the system. In biological systems, metabolic processes like cellular respiration release heat, which helps maintain body temperature but cannot be used for work. Reasons for Incorrect Answers: A) The first law of thermodynamics – This law states that energy cannot be created or destroyed , only transformed, but it does not explain why energy is lost as heat. C) Gibbs free energy equation – This equation (ΔG = ΔH - TΔS) predicts whether a reaction is spontaneous , but it does not describe energy loss as heat. D) The law of conservation of mass – This applies to matter , stating that mass is neither created nor destroyed in a chemical reaction, and does not relate to energy loss. Question 17
A) It generates new energy in the cell – Incorrect , because energy cannot be created (first law of thermodynamics). Instead, ATP transfers energy from one form to another. C) It prevents entropy from increasing – Incorrect , as ATP hydrolysis actually increases entropy by breaking a high-energy molecule into simpler components. D) It allows the cell to maintain equilibrium – Incorrect , as ATP hydrolysis prevents equilibrium by continuously fueling biological processes. Question 19 A biochemist is studying an enzyme-catalyzed reaction and finds that it has a very high activation energy. What role does an enzyme play in this reaction? A) It increases the activation energy to make the reaction more efficient B) It decreases the activation energy to speed up the reaction C) It alters the Gibbs free energy (ΔG) of the reaction D) It provides ATP to power the reaction Correct Answer: B) It decreases the activation energy to speed up the reaction Explanation: Enzymes are biological catalysts that lower activation energy , allowing reactions to occur faster and at physiological temperatures. They achieve this by stabilizing the transition state and reducing energy barriers. Reasons for Incorrect Answers: A) It increases the activation energy to make the reaction more efficient – Incorrect , because enzymes lower activation energy, not increase it. C) It alters the Gibbs free energy (ΔG) of the reaction – Incorrect , because enzymes do not change ΔG ; they only affect the reaction rate. D) It provides ATP to power the reaction – Incorrect , because enzymes do not provide energy ; they catalyze reactions by lowering activation energy. Question 20 Which of the following best explains why metabolic reactions in cells do not reach equilibrium? A) Cells maintain a constant flow of reactants and products B) Enzymes prevent equilibrium from being achieved C) Equilibrium is reached only when a cell dies D) Gibbs free energy remains constant in metabolic reactions Correct Answer: A) Cells maintain a constant flow of reactants and products
Explanation: Cells are open systems , meaning they constantly exchange materials with their environment. Reactants (e.g., glucose, oxygen) enter cells , while products (e.g., CO₂, ATP) are continuously removed , preventing equilibrium. If metabolic reactions reached equilibrium, energy production would stop , and the cell would die. Reasons for Incorrect Answers: B) Enzymes prevent equilibrium from being achieved – Incorrect , because enzymes speed up reactions but do not affect equilibrium position. C) Equilibrium is reached only when a cell dies – Partially true , but the correct reason is the continuous flow of reactants and products, not just cell death. D) Gibbs free energy remains constant in metabolic reactions – Incorrect , because ΔG changes depending on reaction conditions and energy demands. Question 21 A scientist is studying energy transfer in metabolic pathways. He observes that a metabolic reaction requires ATP hydrolysis to proceed. What does this indicate about the reaction? A) It is exergonic and occurs spontaneously B) It is endergonic and requires an energy input C) It is at equilibrium and does not require ATP D) It is a catabolic reaction that releases energy Correct Answer: B) It is endergonic and requires an energy input Explanation: Endergonic reactions have a positive ΔG and require energy input to proceed. ATP hydrolysis ( ATP → ADP + Pi ) releases energy (~7.3 kcal/mol), which can be coupled to an endergonic reaction to drive it forward. Example: Glucose phosphorylation (glucose → glucose-6-phosphate) requires ATP hydrolysis. Reasons for Incorrect Answers: A) It is exergonic and occurs spontaneously – Incorrect , because exergonic reactions release energy and occur without ATP input. C) It is at equilibrium and does not require ATP – Incorrect , because equilibrium reactions have ΔG = 0 and do not require ATP hydrolysis. D) It is a catabolic reaction that releases energy – Incorrect , because catabolic reactions break down molecules and release energy , whereas this is an energy-requiring process.
This process occurs in glycolysis and the citric acid cycle , without the need for an electron transport chain or oxygen. Example: Phosphoenolpyruvate (PEP) donates a phosphate to ADP to form ATP. Reasons for Incorrect Answers: A) Oxidative phosphorylation – Incorrect , because this process occurs in the mitochondria , requires the electron transport chain (ETC) , and depends on oxygen. C) Proton gradient-driven ATP synthesis – Incorrect , because ATP synthase in the ETC relies on a proton gradient to produce ATP. D) Beta-oxidation of fatty acids – Incorrect , because beta-oxidation generates NADH and FADH₂ , which later drive ATP synthesis in the ETC , not by substrate-level phosphorylation. Question 24 A metabolic reaction results in the formation of heat as a byproduct. According to the laws of thermodynamics, what does this suggest about the reaction? A) It is 100% efficient in energy transfer B) Some energy is lost as heat, increasing entropy C) Heat formation indicates an anabolic process D) It must be an endergonic reaction Correct Answer: B) Some energy is lost as heat, increasing entropy Explanation: The second law of thermodynamics states that some energy is always lost as heat during energy transformations, contributing to increased entropy (disorder). In metabolic reactions, excess energy not captured in ATP formation is released as heat, which helps maintain body temperature. Example: Muscle contractions generate heat, warming the body. Reasons for Incorrect Answers: A) It is 100% efficient in energy transfer – Incorrect , because no energy transformation is 100% efficient ; some energy is always lost as heat. C) Heat formation indicates an anabolic process – Incorrect , because catabolic reactions (e.g., glycolysis, cellular respiration) generate heat , not anabolic reactions. D) It must be an endergonic reaction – Incorrect , because endergonic reactions require energy input , while heat is usually a product of exergonic reactions.
Question 25 Which of the following best describes how exergonic and endergonic reactions are linked in cellular metabolism? A) Exergonic reactions release energy that drives endergonic reactions B) Endergonic reactions fuel exergonic reactions C) Both exergonic and endergonic reactions occur independently in cells D) Endergonic reactions occur spontaneously without requiring energy Correct Answer: A) Exergonic reactions release energy that drives endergonic reactions Explanation: Energy coupling allows exergonic reactions (ΔG < 0) , such as ATP hydrolysis , to provide energy for endergonic reactions (ΔG > 0) that require energy input. Example: ATP hydrolysis (exergonic) drives protein synthesis (endergonic). Reasons for Incorrect Answers: B) Endergonic reactions fuel exergonic reactions – Incorrect , because endergonic reactions require energy , they do not provide it. C) Both exergonic and endergonic reactions occur independently in cells – Incorrect , because cells couple reactions to maximize efficiency. D) Endergonic reactions occur spontaneously without requiring energy – Incorrect , because endergonic reactions require ATP or another energy source to proceed. Summary of Concepts Covered in Questions 21-25: Endergonic reactions require ATP input and are driven by exergonic reactions. Catabolic reactions (e.g., glycolysis) break down molecules to release energy. Substrate-level phosphorylation produces ATP without the electron transport chain. Energy transformations always lose some energy as heat, increasing entropy. Exergonic and endergonic reactions are coupled to maintain cellular function. Question 26 A scientist is studying the breakdown of glucose into pyruvate in muscle cells. This process does not require oxygen and generates a small amount of ATP. What type of metabolic pathway is being studied? A) Gluconeogenesis B) Glycolysis
D) It must be a catabolic reaction – Incorrect , because catabolic reactions break down molecules and release energy , while this reaction requires energy input. Question 28 A researcher observes that metabolic reactions often involve the transfer of phosphate groups. Which of the following best describes the function of phosphorylation in metabolism? A) It always inhibits enzymatic activity B) It activates or deactivates enzymes and transfers energy C) It serves only as a structural modification of proteins D) It is independent of ATP hydrolysis Correct Answer: B) It activates or deactivates enzymes and transfers energy Explanation: Phosphorylation (addition of a phosphate group) is a key regulatory mechanism in metabolism. It can activate or inhibit enzymes (e.g., glycogen phosphorylase is activated by phosphorylation). ATP transfers high-energy phosphate groups to molecules, enabling energy coupling. Reasons for Incorrect Answers: A) It always inhibits enzymatic activity – Incorrect , because phosphorylation can either activate or inhibit enzymes. C) It serves only as a structural modification of proteins – Incorrect , because phosphorylation plays a functional role in energy transfer and enzyme regulation , not just structural changes. D) It is independent of ATP hydrolysis – Incorrect , because phosphorylation often involves ATP hydrolysis for energy transfer. Question 29 Which of the following correctly describes how ATP functions as an energy carrier in cells? A) It directly releases electrons for oxidation-reduction reactions B) It stores energy in its phosphate bonds, which release energy upon hydrolysis C) It serves as a long-term energy storage molecule like glycogen D) It is only produced in mitochondria and requires oxygen Correct Answer: B) It stores energy in its phosphate bonds, which release energy upon hydrolysis Explanation:
ATP consists of three phosphate groups , and breaking the terminal phosphate bond ( ATP → ADP + Pi ) releases energy (~7.3 kcal/mol). This energy powers muscle contraction, active transport, and biosynthesis. Reasons for Incorrect Answers: A) It directly releases electrons for oxidation-reduction reactions – Incorrect , because electron carriers like NADH and FADH₂ function in redox reactions, not ATP. C) It serves as a long-term energy storage molecule like glycogen – Incorrect , because ATP is a short-term energy carrier ; glycogen and fat are used for long-term storage. D) It is only produced in mitochondria and requires oxygen – Incorrect , because ATP is also produced in glycolysis (cytoplasm) and does not always require oxygen. Question 30 Which of the following statements about coupled reactions in metabolism is correct? A) An exergonic reaction releases energy to drive an endergonic reaction B) Endergonic reactions release energy that fuels exergonic reactions C) Coupled reactions occur only in the presence of enzymes D) All metabolic reactions are coupled to ATP hydrolysis Correct Answer: A) An exergonic reaction releases energy to drive an endergonic reaction Explanation: In coupled reactions, an exergonic reaction (ΔG < 0) provides the energy needed for an endergonic reaction (ΔG > 0). Example: ATP hydrolysis (exergonic) fuels glucose phosphorylation (endergonic). Reasons for Incorrect Answers: B) Endergonic reactions release energy that fuels exergonic reactions – Incorrect , because endergonic reactions require energy , they do not release it. C) Coupled reactions occur only in the presence of enzymes – Incorrect , because although enzymes speed up reactions , coupling can still occur without them. D) All metabolic reactions are coupled to ATP hydrolysis – Incorrect , because not all reactions require ATP hydrolysis ; some are driven by other mechanisms (e.g., proton gradients). Summary of Concepts Covered in Questions 26-30: Glycolysis is an anaerobic process that generates ATP without oxygen. Endergonic reactions require energy input, while exergonic reactions release energy.
