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Questions and Answers
What role does isoleucine play in the enzyme threonine deaminase?
What role does isoleucine play in the enzyme threonine deaminase?
What happens to threonine deaminase when isoleucine binds to it?
What happens to threonine deaminase when isoleucine binds to it?
Which of the following correctly describes cofactors?
Which of the following correctly describes cofactors?
How do coenzymes assist enzymes in biochemical reactions?
How do coenzymes assist enzymes in biochemical reactions?
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What will occur if the concentration of isoleucine decreases in a cell?
What will occur if the concentration of isoleucine decreases in a cell?
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What role do enzymes play in chemical reactions?
What role do enzymes play in chemical reactions?
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What is the significance of the active site in enzyme function?
What is the significance of the active site in enzyme function?
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How do enzymes lower the activation energy of a chemical reaction?
How do enzymes lower the activation energy of a chemical reaction?
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Which of the following correctly describes the induced-fit model?
Which of the following correctly describes the induced-fit model?
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What happens to enzyme activity as temperature increases?
What happens to enzyme activity as temperature increases?
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What is the correct function of a hydrolase enzyme?
What is the correct function of a hydrolase enzyme?
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Which statement describes the lock and key model for enzymes?
Which statement describes the lock and key model for enzymes?
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In what type of reaction do enzymes facilitate the formation of bonds between substrates?
In what type of reaction do enzymes facilitate the formation of bonds between substrates?
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What is the optimal temperature for enzyme activity in humans?
What is the optimal temperature for enzyme activity in humans?
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How does pH affect enzyme activity?
How does pH affect enzyme activity?
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What occurs when substrate concentration increases beyond a certain point?
What occurs when substrate concentration increases beyond a certain point?
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What distinguishes a competitive inhibitor from a non-competitive inhibitor?
What distinguishes a competitive inhibitor from a non-competitive inhibitor?
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What is the function of allosteric activators?
What is the function of allosteric activators?
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What is feedback inhibition?
What is feedback inhibition?
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Which of the following statements correctly describes enzyme denaturation?
Which of the following statements correctly describes enzyme denaturation?
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Which of the following factors does NOT affect enzyme activity?
Which of the following factors does NOT affect enzyme activity?
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Study Notes
Enzymes
- Enzymes are protein catalysts that speed up chemical reactions by lowering activation energy.
- Enzymes are not used up during a reaction.
- Enzymes are specific to a particular substrate (reactant).
- Enzymes function by lowering the activation energy needed to break bonds between reactant molecules.
- Enzymes can add or remove protons.
- Enzymes can twist or bend molecules.
- Enzymes can increase the probability of molecules coming in close proximity and reacting.
Enzyme Nomenclature
- Enzymes are named for the molecule acted upon with the suffix "-ase" (hydrolytic enzymes).
- For example, amylase breaks down starch, lactase catalyzes lactose, and peptidase breaks peptide bonds.
- Many enzymes also end with "in" e.g. trypsin, pepsin.
Lock and Key Model
- Enzymes are specialized for a particular type of reaction.
- The substrate and the active site must possess complementary shapes for binding to occur.
Induced-Fit Model
- Enzymes can slightly change their shape to better accommodate the substrate.
- This is known as induced fit.
How Enzymes Lower Activation Energy
- Enzymes form enzyme-substrate complexes.
- Substrates bind to the active site on the enzyme.
- The active site undergoes a slight conformation change (induced fit) to better accommodate the substrate.
Enzyme-Substrate Complex and Activation Energy
- In catabolic reactions, the interactions between the substrate and enzyme cause stress or distortion of the bonds in the substrate, allowing them to break.
- In anabolic reactions, the enzyme allows two substrates to have the proper orientation for bonds to form between them.
Factors Affecting Enzyme Activity
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Temperature:
- As temperature rises, reacting molecules gain more kinetic energy which increases the chances of successful collisions.
- This increases the rate of the reaction.
- Enzymes have an optimal temperature for their activity. In humans, the optimal temperature is 37°C.
- At temperatures higher than optimal, enzymes denature.
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pH:
- Enzymes work within a very small pH range.
- Optimal pH is the level where an enzyme performs at its greatest activity.
- pH levels outside of the optimal range can cause denaturation.
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Concentration of substrate and enzyme:
- The rate of reaction increases with an increase in either the substrate or enzyme concentration.
- Eventually, all of the active sites of the enzymes become occupied and the reaction reaches saturation.
- To continue the reaction, an enzyme-substrate complex must dissociate to free up an active site.
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Inhibition:
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Competitive Inhibitors:
- Similar to the enzyme's substrate and can bind to the active site, blocking the normal substrate.
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Non-competitive Inhibitors:
- Bind to the enzyme at an allosteric site (not the active site) and cause a conformational change, preventing the normal substrate from binding.
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Competitive Inhibitors:
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Allosteric Regulation:
- Cells control enzyme activity to coordinate cellular activities.
- Activators can bind to allosterically controlled enzymes to stabilize its shape, keeping all active sites available.
- Allosteric inhibitors can bind to allosterically controlled enzymes to stabilize the inactive form of the enzyme.
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Feedback Inhibition:
- This method is used by cells to control metabolic pathways involving a series of reactions.
- A product formed later in the sequence allosterically inhibits an enzyme that catalyzes a reaction earlier in the pathway.
- Feedback inhibition prevents too much buildup of product.
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Cofactors and Coenzymes:
- Required by some enzymes to function.
- Bind to the active sites of enzymes.
- Cofactors are inorganic, non-protein components. They usually attract electrons in the substrate to assist in breaking bonds (e.g. Zn²⁺ and Mn²⁺).
- Coenzymes are organic, non-protein molecules, such as the derivatives of many vitamins. They often shuttle molecules from one enzyme to another (e.g. vitamin B₃ is a coenzyme of NAD⁺).
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Description
This quiz covers the essential concepts of enzymes, including their role as protein catalysts, their specific naming conventions, and the models explaining their interactions with substrates. Test your knowledge on enzyme functionality and nomenclature.
