Questions and Answers
What best characterizes the role of ATP in cellular metabolism?
The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways?
A chemical reaction is designated as exergonic rather than endergonic when _____?
Which of the following is changed by the presence of an enzyme in a reaction?
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What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction?
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How do enzymes lower activation energy?
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Enzymes speed up the rate of the reaction without changing the (change in) G for the reaction.
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Which of the following statements about enzyme function is correct?
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A plot of reaction rate against temperature for an enzyme indicates little activity at 10°C and 45°C, with peak activity at 35°C. The most reasonable explanation for the low velocity at 10°C is that _____.
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An enzyme is consumed during the reaction it catalyzes.
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Which of the following statements about the active site of an enzyme is correct?
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What is meant by the 'induced fit' of an enzyme?
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Which of the following statements correctly describe(s) the role(s) of heat in biological reactions?
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Which of the following would lead to a faster conversion of substrate into product under saturated conditions?
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Which of the following environments or actions would not affect the rate of an enzyme reaction?
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Enzyme activity is affected by pH because _____.
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Which of these statements about enzyme inhibitors is true?
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Which of the following correctly explains why the addition of succinylcholine decreases the rate of acetylcholine hydrolysis?
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The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of _____?
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Which of the following statements about allosteric proteins is/are true?
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The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Why does this decrease occur?
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Under most conditions, the supply of energy by catabolic pathways is regulated by the demand for energy by anabolic pathways. Which of the following statements is most likely to be true?
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Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as ___________ is to ___________.
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Most cells cannot harness heat to perform work because
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Which of the following metabolic processes can occur without a net influx of energy from some other process?
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If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to ____________.
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Some bacteria are metabolically active in hot springs because
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If an enzyme is added to a solution where its substrate and product are in equilibrium, what would occur?
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Which of the following correctly states the relationship between anabolic and catabolic pathways?
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Which of the following situations represent(s) a transformation of one type of energy to another?
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Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description?
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Which of the following states the relevance of the first law of thermodynamics to biology?
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Which of the following is an example of the second law of thermodynamics as it applies to biological reactions?
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According to the second law of thermodynamics, which of the following is true?
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If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously?
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Which one of the following has the most free energy per molecule?
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Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous?
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If, during a process, the system becomes more ordered, then _____
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When one molecule is broken down into six component molecules, which one of the following will always be true?
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From the equation ΔG = ΔH - TΔS it is clear that _____
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What must be true if the reaction AB + CD → AC + BD occurs spontaneously?
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From the equation ΔG = ΔH - TΔS it is clear that __________.
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An exergonic (spontaneous) reaction is a chemical reaction that _____
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Which of the following reactions would be endergonic?
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Which of the following processes tend to keep metabolic pathways away from equilibrium?
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Which of the following is an example of the cellular work involved in the production of electrochemical gradients?
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In general, the hydrolysis of ATP drives cellular work by _____.
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Which of the following statements correctly describes some aspect of ATP hydrolysis being used to drive the active transport of an ion into the cell against the ion's concentration gradient?
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Much of the suitability of ATP as an energy intermediary is related to the instability of the bonds between the phosphate groups. These bonds are unstable because _____
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When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations?
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Study Notes
Exergonic and Endergonic Reactions
- Catabolism is an exergonic process, releasing energy; anabolism is endergonic, requiring energy.
- Example: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O represents a reaction that occurs without additional energy input.
Enzymatic Activity
- When an enzyme is saturated with substrate, adding more enzyme speeds up reaction rates.
- Optimal temperatures for some bacteria allow their enzymes to function effectively in extreme heat, such as hot springs.
Thermodynamics in Organisms
- Organisms are thermodynamically open systems, exchanging energy with their surroundings.
- The second law of thermodynamics states that the entropy decrease in living organisms is balanced by increased entropy in their environment.
ATP and Energy
- ATP hydrolysis releases energy that is coupled to drive endergonic reactions.
- The free energy from ATP hydrolysis can be used for cellular work, such as transporting protons against their gradient.
- Stability of ATP's phosphate bonds is due to repulsive forces between negatively charged groups.
Free Energy Changes (ΔG)
- ΔG indicates whether reactions are spontaneous. A negative ΔG means a spontaneous reaction.
- Reactions that lead to increased molecular organization (decrease in entropy) are typically endergonic.
Energy Coupling and Metabolic Pathways
- Continuous removal of metabolic products and external energy input keeps pathways away from equilibrium.
- The hydrolysis of ATP is crucial in coupling exergonic reactions to more energy-demanding processes.
Chemical Reaction Designations
- Exergonic reactions release energy; they occur spontaneously when the potential energy of products is less than that of the reactants.
- Enzymes lower the activation energy needed for reactions but do not change ΔG.
Additional Facts
- The transformation of energy types (e.g., chemical to mechanical) occurs in various processes, such as photosynthesis and combustion.
- An example of endergonic reaction is the synthesis of sucrose from glucose and fructose.
Summary of Thermodynamic Principles
- Energy input is necessary to maintain low entropy in living systems.
- The first law of thermodynamics states that energy can transform forms but total energy remains constant.
- Understanding energy dynamics is critical for analyzing cellular metabolic functions and reactions.### Gibbs Free Energy (ΔG)
- ΔG indicates the spontaneity of a reaction; its sign determines if a reaction is spontaneous.
- The magnitude of ΔG does not correlate with the reaction speed.
- Enzymes do not change the ΔG but can influence the rate of reactions by lowering activation energy.
Enzyme Function
- Enzymes lower activation energy by locally concentrating reactants.
- They produce an enzyme-substrate complex but are not consumed during the catalytic process.
- Enzymes are crucial in both anabolic and catabolic reactions and exhibit specificity towards substrates.
Activation Energy
- Lower temperatures (e.g., 10°C) result in less enzymatic activity due to insufficient activation energy.
- The shape of enzyme active sites is flexible, allowing slight changes when substrates bind (induced fit).
Temperature and Enzyme Activity
- Enzyme activity generally increases with temperature until a peak is reached, after which it may diminish.
- Certain conditions (e.g., excessive heat or cold) can denature enzymes, affecting their function.
pH Impact
- Enzyme activity is sensitive to pH; extreme pH conditions can disrupt hydrogen bonds, altering the active site's shape.
- Enzymes have optimal pH ranges for activity, outside of which activity declines.
Inhibition Mechanisms
- Competitive inhibitors resemble substrates and bind to the active site, competing for binding; their effects can be reversed by increasing substrate concentration.
- Noncompetitive inhibitors bind to alternative sites, influencing enzyme activity without competing with the substrate.
- Allosteric regulation involves inhibitors or activators affecting enzyme shape and function through binding at sites distinct from the active site.
Allosteric Regulation
- Allosteric proteins exist in active/inactive forms and respond to environmental changes and inhibitor action.
- High levels of ADP can stimulate catabolic pathways, driving energy production aligned with anabolic demands.
Summary of Key Points
- Enzymes are essential biological catalysts that accelerate reactions without being consumed.
- Their activity depends on environmental conditions such as temperature and pH, which can alter enzyme structure and functionality.
- The mechanisms of inhibition (competitive and noncompetitive) play significant roles in regulating metabolic pathways.
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Test your understanding of crucial concepts in Biology Chapter 8 with these flashcards. Focus on key terms like exergonic and endergonic as you explore the relationship between catabolism and anabolism. Perfect for reinforcing your knowledge in cellular processes.