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Questions and Answers
What is the role of an enzyme in a chemical reaction?
What is the role of an enzyme in a chemical reaction?
What occurs when the enzyme-substrate complex is formed?
What occurs when the enzyme-substrate complex is formed?
What is meant by the term 'induced fit' in enzyme action?
What is meant by the term 'induced fit' in enzyme action?
Which of the following describes the specificity of enzymes?
Which of the following describes the specificity of enzymes?
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What components make up a complete enzyme that requires a cofactor?
What components make up a complete enzyme that requires a cofactor?
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What is a coenzyme?
What is a coenzyme?
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At what temperature do human enzymes generally function most effectively?
At what temperature do human enzymes generally function most effectively?
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What is the optimal pH range for most human enzymes?
What is the optimal pH range for most human enzymes?
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How do enzymes affect activation energy?
How do enzymes affect activation energy?
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Which of the following statements about enzyme and substrate concentration is accurate?
Which of the following statements about enzyme and substrate concentration is accurate?
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Study Notes
Enzymes
- Enzymes are biological catalysts, increasing the speed of chemical reactions without being consumed by the reaction, speeding up metabolic reactions.
- Most enzymes are proteins.
- Each enzyme acts on a specific substrate.
Enzyme-Substrate Complex
- Enzymes function by forming an unstable intermediate complex with the substrate (the substance acted upon).
- When the enzyme-substrate complex (ES complex) breaks down, the product is released, and the original enzyme is regenerated, ready to form a new ES complex.
- Every enzyme is characterized by one or more active sites. These are regions where the substrate binds to form the enzyme-substrate complex.
Induced Fit
- Enzyme shape isn't exactly complementary to the substrate.
- Substrate binding causes a change in the enzyme's shape known as induced fit.
- Induced fit helps break and form bonds.
Enzyme Naming
- Scientists often add the suffix -ase to the name of the substrate to name enzymes.
- Example: Sucrase acts on sucrose, maltase acts on maltose.
Enzyme Specificity
- Enzymes are specific; a specific enzyme for each substrate.
- The enzyme urease decomposes urea to ammonia and carbon dioxide, not other substrates.
- Sucrase splits only sucrose.
Co-factors
- Some enzymes consist solely of proteins (apoenzymes).
- Other enzymes have additional components (cofactors): organic or inorganic molecules (eg Mg, Ca ions) that are needed to help the enzyme function.
- Neither apoenzyme nor cofactor alone has catalytic activity; only when combined does the enzyme function properly.
- A cofactor that is organic and non-polypeptide is a coenzyme.
- Many vitamins are coenzymes or parts of coenzymes.
Optimal Temperature
- Each enzyme has an optimal temperature for the fastest reaction rate.
- Enzymatic activity increases with temperature up to an optimal point.
- At lower temperatures, enzymatic reactions proceed slowly or not at all; enzymes are inactive at 0°C.
- In humans, the optimal temperature is between 35-40°C.
- Above 50°C, human enzymes are destroyed (denatured).
- Heat-tolerant bacteria and archaea have different optimal temperatures (70-80°C).
Optimal pH
- Most enzymes operate within a narrow pH range with an optimal pH for their fastest reaction rate.
- Optimal pH in most human enzymes is between 6 and 8.
- Example: Pepsin (acid medium, pH 2) is a protein-digesting enzyme in the stomach.
- Example: Trypsin (basic medium, pH 8) is an enzyme splitting proteins in the small intestine.
- Example: Salivary amylase (neutral pH 7) acts on starch.
Activation Energy
- All reactions need activation energy (energy needed to break existing bonds and start a reaction).
- Enzymes lower activation energy requirement, speeding up reactions.
- The graph shows how enzymes reduce the energy barrier to start a reaction.
Enzyme and Substrate Concentration
- Enzyme activity is regulated.
- Constant pH and temperature, reaction rate depends on concentrations of enzyme and substrate.
- Rate increases proportionally to enzyme concentration, if substrate is in excess.
- If enzyme concentration is high, then rate is proportional to substrate concentration, until the enzymes are saturated.
Enzyme Inhibition
- Reversible inhibition: An inhibitor forms weak bonds with the enzyme.
- Competitive inhibition: The inhibitor competes with the substrate for the active site.
- Noncompetitive inhibition: The inhibitor binds to a site other than the active site, changing the enzyme's shape so it cannot bind to the substrate.
- Irreversible inhibition: The inhibitor combines with the enzyme and permanently inactivates it. (e.g., mercury, lead).
Evaluation
- A is the substrate; E is the product; C is the enzyme.
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Description
Explore the fascinating world of enzymes, their role as biological catalysts, and how they interact with substrates. This quiz covers the enzyme-substrate complex, the concept of induced fit, and common naming conventions for enzymes. Test your knowledge of these essential proteins and their functions in metabolic reactions.
