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Questions and Answers
How do enzymes lower the activation energy needed for reactions to proceed?
What is the initial effect of increasing enzyme concentration on the rate of reaction?
What is typically measured to investigate the progress of an enzyme-catalyzed reaction?
In an investigation comparing enzyme concentrations, what should be kept constant?
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What happens to the initial rate of reaction once the substrates become limiting factors?
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What role do the R groups of amino acids in the active site of an enzyme play?
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How frequently should samples be taken during an enzyme-catalyzed reaction investigation?
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Which statement best describes the relationship between enzyme concentration and the rate of reaction?
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What is the purpose of plotting a graph with dependent and independent variables during the reaction?
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What complication arises when comparing reactions with different substrate concentrations over time?
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What is the primary function of enzymes in biological reactions?
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What determines the specificity of an enzyme?
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Which of the following is NOT a factor maintaining the 3-dimensional structure of an enzyme?
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What happens to the enzyme after a substrate is converted into products?
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In the induced fit model of enzyme activity, what occurs after the substrate binds?
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What is the role of the enzyme-substrate complex?
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Which type of interactions primarily help enzymes lower activation energy?
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What is activation energy?
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How are substrates initially held in the active site of an enzyme?
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Which of the following statements about enzymes is false?
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What is the significance of the specific active site of an enzyme?
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Which type of bond plays a role in maintaining the tertiary structure of enzymes?
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In the induced fit model, what occurs after the substrate binds to the enzyme's active site?
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How does an enzyme facilitate a reaction without being consumed?
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What happens during the formation of the enzyme-substrate complex?
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Study Notes
Enzymes - Biological Catalysts
- Enzymes are globular proteins that act as biological catalysts, speeding up chemical reactions by lowering activation energy.
- Enzymes remain unchanged at the end of the reaction.
- Enzymes are highly specific in their functions due to their active sites.
- Most enzymes have a tertiary structure, essential for their catalytic activity.
- A few enzymes have a quaternary structure.
Specificity of Enzymes
- The specificity of enzymes arises from their active sites, determined by the sequence of amino acids in the polypeptide chain.
- The specific folding and coiling of the polypeptide chain creates a precise 3D shape, bringing specific amino acids together.
- This precise shape is maintained by various bonds:
- Hydrogen bonds between polar groups (NH- and CO-)
- Ionic bonds between ionized amine and carboxylic acid groups
- Disulfide bonds between cysteine (-SH) groups
- Hydrophobic interactions between non-polar side chains
Enzyme-Substrate Complex
- Enzymes have specific active sites that are complementary in shape to their substrates.
- The substrate binds to the active site, forming an enzyme-substrate complex.
- This binding is facilitated by temporary hydrogen bonds.
- The binding causes strain or stress in the substrate, lowering the activation energy.
- The products of the reaction no longer fit the active site and are released, leaving the enzyme unchanged.
Induced Fit Model
- The induced fit model describes the mechanism of enzyme action in more detail.
- The substrate is not perfectly complementary to the active site initially.
- The active site changes shape slightly upon substrate binding, molding and folding around it.
- This change in shape creates a better fit, allowing the formation of a more stable enzyme-substrate complex.
- The R groups of amino acids in the active site interact strongly with the substrate.
- This interaction can lead to the break down of the substrate or the formation of bonds between molecules, resulting in products.
Lowering Activation Energy
- The activation energy is the minimum energy required for reactants to reach the unstable transition state and convert into products.
- Without enzymes, many reactions in living cells would be too slow at normal body temperature (37°C).
- Enzymes lower the activation energy by:
- Providing an alternative pathway for the reaction.
- Bringing reactants closer together in the active site, forming the enzyme-substrate complex.
- The R groups of amino acids in the active site interact with the substrate, putting strain on it.
- This strain makes it easier for bonds in the substrate to break or form, leading to products.
Investigating Enzyme Activity
- To investigate the progress of an enzyme-catalyzed reaction:
- Start with known concentrations of substrate and enzyme.
- Control other variables like pH and temperature.
- Take samples at regular intervals (e.g., every 5 minutes).
- Plot a graph with the dependent variable (substrate or product concentration) on the y-axis and time on the x-axis.
- Determine the rate of disappearance of substrate or appearance of product from the graph.
- The initial rate of the reaction can also be determined from the graph.
Factors Affecting Enzyme Activity
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Enzyme Concentration:
- The initial rate of reaction increases linearly with an increase in enzyme concentration.
- This is due to the increased number of active sites available for substrate binding.
- The initial rate is directly proportional to the enzyme concentration, provided all other factors remain constant.
- This linear increase continues as long as there is sufficient substrate available.
Enzymes: Biological Catalysts
- Enzymes are globular proteins that speed up chemical reactions by lowering the activation energy without being changed themselves.
- Active Site: Enzymes have specific active sites, which are regions that bind to substrates and facilitate reactions. The active site's shape is determined by the amino acid sequence and folding of the polypeptide chain.
- Specificity: This precise 3D structure of the active site makes each enzyme specific for a particular substrate.
- Tertiary and Quaternary Structure: Most enzymes have a tertiary structure, while a few have a quaternary structure.
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Factors maintaining Active Site Structure:
- Hydrogen bonds between polar groups (NH- and CO-)
- Ionic bonds between ionized amine and carboxylic acid groups.
- Disulfide bonds between cysteine (S-H) groups.
- Hydrophobic interactions between non-polar side chains.
Enzyme Action: Converting Substrate to Products
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Lock and Key Model:
- Enzyme's active site has a specific shape complementary to the substrate.
- Substrate fits into the active site and forms temporary hydrogen bonds, creating an Enzyme-Substrate complex.
- This causes strain/stress in the substrate, lowering the activation energy needed for the reaction.
- The products are released because they no longer fit the active site, and the enzyme remains unchanged.
Induced Fit Mechanism
- Partial Complementarity: The substrate is partially complementary to the active site.
- Shape Change: The active site changes its shape slightly when the substrate binds, molding around it.
- Improved Fit: This interaction strengthens the bond between the active site and the substrate.
- Enzyme-Substrate Complex Formation: Allows for the formation of an Enzyme-Substrate complex.
- R-group Interaction: The R groups of the amino acids in the active site interact with the substrate.
- Product Formation: This interaction can cause substrate breakdown or encourage bond formation between molecules, leading to the formation of one or more products.
Activation Energy and Enzyme Action
- Activation Energy: The minimum energy required for reactants to start a chemical reaction.
- Role of Enzymes: Enzymes lower the activation energy needed for a reaction to occur at a reasonable rate within the body.
- Alternative Pathway: Enzymes provide an alternative reaction pathway with a lower activation energy.
- Proximity: Enzymes bring reactants together in the active site, forming the Enzyme-Substrate complex.
- Strain: The R groups of the amino acids in the active site interact with the substrate, putting strain on the reactants.
- Product Formation: This strain makes it easier for bonds in the substrate to be broken or formed, resulting in product formation.
Investigating Enzyme Activity
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Controlled Experiment Setup:
- Start with known concentrations of substrate and enzyme.
- Control variables like pH and temperature.
- Take samples at regular time intervals (e.g., every 5 minutes).
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Data Analysis:
- Plot a graph with the dependent variable (substrate or product concentration) on the y-axis and time on the x-axis.
- Determine the rate of disappearance of substrate or the rate of appearance of product.
- Calculate the initial rate of reaction.
Factors Affecting Enzyme Activity: Enzyme Concentration
- Experiment: Different concentrations of catalase enzyme are added to the same volume of hydrogen peroxide solution.
- Trend: The initial rate of reaction increases linearly with an increase in enzyme concentration, as long as the substrate is present.
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Explanation: A higher enzyme concentration means:
- More active sites available for substrate binding.
- More successful collisions between enzyme and substrate.
- More Enzyme-Substrate complexes formed.
- Higher reaction rate.
Key Point
- The reaction rate will eventually plateau as the enzyme concentration increases due the substrate becoming the limited factor, not the enzyme.
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Description
Explore the fascinating world of enzymes, the biological catalysts that accelerate chemical reactions in living organisms. This quiz delves into enzyme specificity, structures, and the roles of active sites. Test your knowledge on how these protein catalysts maintain their activity throughout various chemical processes.
