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Questions and Answers
Which of the following is NOT a classification of enzymes?
What do oxidoreductases catalyze?
Oxidation/reduction reactions
What is the role of transferases?
Transfer the functional groups
What type of reactions do hydrolases catalyze?
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Which enzyme classification involves the joining of two molecules by the synthesis of new bonds?
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Extracellular enzymes are nonfunctional plasma enzymes.
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Which enzyme is associated with the diagnosis of liver function?
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What model describes the specific geometric fit between an enzyme and its substrate?
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Who proposed the induced fit model of enzyme-substrate interaction?
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What process can lead to competitive inhibition of enzyme activity?
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Study Notes
Enzyme Classification
- Enzymes are classified into six major classes based on the type of reaction they catalyze:
- Oxidoreductases: Catalyze oxidation-reduction reactions, transferring hydrogen and oxygen atoms or electrons.
- Transferases: Transfer functional groups like methyl, acyl, amino, or phosphate groups between molecules.
- Hydrolases: Break down substrates through hydrolysis, forming two products. Peptidases are a notable example.
- Lyases: Catalyze non-hydrolytic addition or removal of groups from substrates, cleaving bonds like C-C, C-N, C-O, or C-S.
- Isomerases: Promote intramolecular rearrangement of atoms within a molecule.
- Ligases (Synthetases): Join two molecules by forming new C-O, C-S, C-N, or C-C bonds while utilizing ATP for energy.
- Translocases: Move ions or molecules across membranes or facilitate their separation within membranes.
Enzyme Localization
- Enzymes can be categorized based on their activity location.
- Intracellular enzymes: Function inside cells and are typically nonfunctional in plasma.
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Extracellular enzymes: Operate outside of cells and can be further classified:
- Secretory enzymes: Functionally active in plasma.
- Excretory enzymes: Nonfunctional in plasma.
Diagnostic Value of Enzymes
- Specific enzyme levels in blood can be used to diagnose various conditions. Some examples include:
- Amylase: High levels may suggest pancreatitis.
- Lipase: Elevated levels often indicate pancreatic problems.
- Alanine aminotransferase (ALT): Increased levels can signal liver damage.
- Aspartate aminotransferase (AST): Raised levels may indicate liver or heart damage.
- Alkaline phosphatase (ALP): Elevated levels can indicate bone disorders, liver disease, or biliary obstruction.
- Creatine kinase (CK): High levels can occur due to muscle damage or heart attack. Different isoforms (MM, BB, MB) provide further diagnostic information.
Enzyme Action and Specificity
- Enzymes accelerate reactions by lowering the activation energy needed to reach the transition state.
- They achieve this by stabilizing the transition state, thus decreasing the energy required to form products.
- Enzyme specificity is crucial and can be categorized:
- Reaction specificity: Enzymes catalyze only a specific type of reaction.
- Substrate specificity: Enzymes bind and act only on specific substrates.
Enzyme-Substrate Interaction
- Lock and Key Model: Proposed by Emil Fischer in 1894, this model describes the enzyme and substrate as perfectly complementary shapes, like a lock and key, that fit together.
- Induced Fit Model: Proposed by Daniel Koshland in 1958, this model suggests that the enzyme's active site is flexible and changes conformation when it binds to the substrate, leading to a better fit.
Active Site and Induced Conformational Change
- The active site is the region of the enzyme responsible for substrate binding and catalysis.
- The enzyme hexokinase provides a classic example of induced conformational change. Its active site undergoes a shape change upon binding to glucose.
Enzyme Kinetics and Inhibition
- Substrate concentration: The rate of an enzyme-catalyzed reaction increases with substrate concentration, but there is a maximum rate that can be achieved.
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Competitive inhibition: Inhibitor molecules compete with the substrate for binding to the active site, reducing reaction rate.
- Effects of competitive inhibition on kinetics: Michaelis-Menten constant (Km) increases, indicating decreased substrate affinity, while the maximum velocity (Vmax) remains unchanged.
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Noncompetitive inhibition: Inhibitor molecules bind to a different site on the enzyme, altering its conformation and reducing its activity.
- Effects of noncompetitive inhibition on kinetics: Both Km and Vmax are affected. Km generally increases due to reduced substrate affinity, and Vmax decreases due to the inhibitor's effect on enzyme activity.
Enzyme Activation and Regulation
- Zymogen activation: Some enzymes are synthesized as inactive precursors called zymogens. Activation occurs through proteolytic cleavage, removing a portion of the molecule and revealing the active site.
- Covalent modifications: Enzymes' activity can be regulated by covalent modifications like phosphorylation, dephosphorylation, or acetylation. These changes can activate or deactivate the enzyme.
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Description
This quiz covers the classification of enzymes into six major classes based on the types of reactions they catalyze, including oxidoreductases, transferases, and more. Additionally, it explores enzyme localization, detailing their functional roles within biological systems. Test your understanding of enzymatic functions and their classifications.
