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Questions and Answers
What type of enzyme category does lactate dehydrogenase belong to?
What type of enzyme category does lactate dehydrogenase belong to?
What does the first number in an EC code represent?
What does the first number in an EC code represent?
Which of the following accurately describes a holoenzyme?
Which of the following accurately describes a holoenzyme?
What is the role of the active site in an enzyme?
What is the role of the active site in an enzyme?
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What term describes the change that occurs in an enzyme upon substrate binding?
What term describes the change that occurs in an enzyme upon substrate binding?
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Which of the following statements is true regarding enzyme specificity?
Which of the following statements is true regarding enzyme specificity?
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What is an allosteric site on an enzyme?
What is an allosteric site on an enzyme?
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Why are many enzymes compartmentalized in specific organelles?
Why are many enzymes compartmentalized in specific organelles?
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What is the primary role of enzymes in biological systems?
What is the primary role of enzymes in biological systems?
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What suffix is commonly associated with enzyme names derived from their substrates?
What suffix is commonly associated with enzyme names derived from their substrates?
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Which of the following terms refers to an enzyme that requires an additional non-protein molecule for activity?
Which of the following terms refers to an enzyme that requires an additional non-protein molecule for activity?
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What is meant by the term 'catalytic efficiency' in relation to enzymes?
What is meant by the term 'catalytic efficiency' in relation to enzymes?
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Which class of enzymes is specifically responsible for the cleavage of covalent bonds?
Which class of enzymes is specifically responsible for the cleavage of covalent bonds?
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Which of the following is an example of an enzyme that has a name signifying its action performed?
Which of the following is an example of an enzyme that has a name signifying its action performed?
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What characteristic of enzymes allows most biochemical reactions in living organisms to occur at physiological temperatures?
What characteristic of enzymes allows most biochemical reactions in living organisms to occur at physiological temperatures?
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What is an apoenzyme?
What is an apoenzyme?
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Where does glycolysis primarily occur?
Where does glycolysis primarily occur?
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What is the term for the number of substrate molecules converted to product per enzyme molecule per second?
What is the term for the number of substrate molecules converted to product per enzyme molecule per second?
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How do enzymes accelerate reaction rates?
How do enzymes accelerate reaction rates?
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What does a lower free energy of activation imply?
What does a lower free energy of activation imply?
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What is the relationship between ΔG in enzyme-catalyzed and uncatalyzed reactions?
What is the relationship between ΔG in enzyme-catalyzed and uncatalyzed reactions?
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What is the transition state in a chemical reaction?
What is the transition state in a chemical reaction?
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What effect do enzymes have on the equilibrium of a chemical reaction?
What effect do enzymes have on the equilibrium of a chemical reaction?
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Which metabolic pathway occurs exclusively in the mitochondrion?
Which metabolic pathway occurs exclusively in the mitochondrion?
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Study Notes
Medical Enzymology
- Enzymes are biological catalysts that increase the rate of chemical reactions.
- Enzymes are mostly proteins, but some are RNA (ribozymes).
- Enzymes are required in small amounts and remain unchanged during reactions.
- All biological functions in living tissues rely on chemical reactions.
- Reactions proceed at 37°C (body temperature) because of enzymes.
- Almost all reactions in living tissues are catalyzed by enzymes.
Intended Learning Outcomes (ILOs)
- Define enzymes, identify enzyme nomenclature, classes, and commission code.
- Identify enzyme-related terms (apoenzyme, holoenzyme, coenzyme, prosthetic group, cofactor).
- Discuss enzyme properties (specificity, catalytic efficiency, subcellular localization, active site, catalytic sites).
- Describe the mechanism of enzyme action (catalysis).
What are Enzymes?
- Enzymes are biological catalysts, increasing the rate of chemical reactions.
- Mostly proteins, with RNA exceptions (like peptidyl transferase).
- Enzymes are needed in small amounts.
- Enzymes are unchanged during reactions.
Why are Enzymes Important?
- Enzyme-mediated chemical reactions are crucial for all living tissue functions.
- Car engines use combustion reactions; our cells use enzymes for similar functions at a much lower temperature.
- Nearly all reactions in living tissues are catalyzed by enzymes.
Enzyme Nomenclature
- Two naming systems exist.
- Common names: the suffix "-ase" is appended to the substrate name (e.g., Urease, Glucosidase). Names might also describe the enzyme's action (e.g., lactate dehydrogenase).
- Systematic names: use the whole chemical reaction’s description in the name, including all substrates. They're long and less common, e.g., lactate:NAD+ oxidoreductase = lactate dehydrogenase.
Classes of Enzymes
- Enzymes are categorized based on their function.
- Oxidoreductases: handle oxidation-reduction reactions. (Example: lactate dehydrogenase)
- Transferases: transfer specific groups between molecules. (Example: aminotransferase)
- Hydrolases: use water to break bonds. (Example: Lipases)
- Lyases: add/remove groups to/from molecules, forming or breaking double bonds. (Example: Aldolase A)
- Isomerases: convert molecules into isomers. (Example: Triose phosphate isomerase)
- Ligases: join molecules using energy (ATP). (Example: Fatty acyl CoA synthetase)
Enzyme Commission Code (EC code)
- Enzyme-related reactions can be specified through EC numbers (assigned by IUBMB).
- These codes have four numbers separated by dots.
- The first number indicates the enzyme class (e.g., 2 = transferase).
Holoenzyme and Apoenzyme
- Apoenzyme: the protein part of an enzyme.
- Holoenzyme: the complete, active enzyme (apoenzyme + non-protein part).
Non-protein parts (Cofactors)
- Cofactors: non-protein components enabling enzyme function.
- Coenzymes: tightly bound, often containing vitamins. (Example: TPP, FMN, FAD)
- Prosthetic groups: tightly bound cofactors. (Example: Biotin)
- Metal ions: loosely or tightly bound metal atoms involved in enzyme action.
- Metalloenzymes: enzymes containing tightly bound metal ions. (Example: Fe in peroxidases)
Enzyme Specificity
- Enzymes usually interact with only one or a few specific substrates.
- Specificity can be based on molecule shape/structure (e.g., isomers, certain types of bonds).
- Some enzymes specifically interact with hydrogen carriers (e.g. NAD+ or FAD). Examples include L-amino acid oxidases that show specificity to L amino acids not D amino acids.
Subcellular Localization
- Many enzymes are located in specific cellular compartments.
- This localization creates optimal conditions for reactions.
- Examples include glycolysis in the cytosol and the Krebs cycle primarily in mitochondria.
Catalytic Efficiency
- Enzymes significantly boost reaction rates compared to un-catalyzed reactions.
- Turnover number (kcat): The speed rate enzyme works , it's how many substrate molecules an enzyme molecule can convert into a product in a given time. (Typically 102 - 104 molecules per second).
Mechanism of Enzyme Action
- Enzymes lower the activation energy needed for a reaction but don't alter the overall reaction's energy changes.
- Active site: Crucial site where substrates bind and reactions occur.
Energy Changes During the Reaction
- Activation energy: The energy needed to start a chemical reaction.
- Transition state: The unstable intermediate step in a reaction.
- Enzyme-catalyzed reactions proceed rapidly because they lower the reaction’s activation energy.
- Enzymes do not change the overall free energy of a reaction ( only the activation energy).
Active Sites Facilitate Catalysis
- Active sites stabilize transition states, which helps products form.
- Catalytic groups at the site can support specific steps in the reaction.
References for Further Readings
- Lippincott Illustrated Review Integrated system 3rd edition
- Lippincott Illustrated Review 6th edition
- Oxford Hand book of Medical Science 2nd edition
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Description
This quiz covers the fundamental concepts of medical enzymology, focusing on the definitions, classifications, and properties of enzymes. Participants will explore enzyme mechanisms, including catalysis and specific terminology used in the field. Gain a deeper understanding of how enzymes function as biological catalysts in living organisms.
