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Questions and Answers
Which of the following characteristics can differ between the microenvironment of an enzyme and the surrounding cytoplasm?
What is the primary benefit of catalysis by proximity?
What is the effect of acid-base catalysis on enzyme-catalyzed reactions?
Which type of acid-base catalysis is sensitive to changes in proton or hydroxide ion concentration?
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Which enzyme family employs two conserved aspartyl residues as acid-base catalysts?
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What is the result of substrate molecules being oriented in a position ideal for chemical interaction?
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What is the estimated rate enhancement of enzyme-catalyzed reactions compared to non-enzyme-catalyzed reactions?
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Which of the following is NOT a mechanism used by enzymes to facilitate catalysis?
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What is the primary function of lactase in milk production?
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What characterizes enzymes in terms of their structure?
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What is the typical effect of enzymes on the rates of noncatalyzed reactions?
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What is a characteristic of enzymes that distinguishes them from other catalysts?
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What is the suffix typically used to designate the name of an enzyme?
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What is the term for enzymes that remove hydrogen atoms from their substrates?
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What is the primary function of stereospecific enzyme catalysts?
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What is the term for enzymes that catalyze the rearrangement of configurations in their substrates?
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What is the primary purpose of the International Union of Biochemistry's enzyme nomenclature system?
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Which of the following enzyme classes catalyzes the transfer of moieties such as glycosyl, methyl, or phosphoryl groups?
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What is the E.C. number of hexokinase according to the IUB system?
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Which of the following enzymes catalyzes geometric or structural changes within a molecule?
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What is the primary function of alphanumeric designators in enzyme names?
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Which of the following enzymes catalyzes the joining together of two molecules in reactions coupled to the hydrolysis of ATP?
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What is the main advantage of the IUB system over earlier naming conventions?
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Which of the following enzymes catalyzes non-hydrolytic cleavage of C-C, C-O, C-N, and other covalent bonds?
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What is the mechanism by which aspartic proteases catalyze peptide bond hydrolysis?
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What is the benefit of strain catalysis?
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What is the outcome of covalent catalysis?
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What is the characteristic of covalent catalysis?
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What type of reactions are commonly catalyzed by covalent catalysis?
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What is the limitation of the 'lock and key model'?
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What is the sequence of events in a 'ping-pong' mechanism?
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What is the role of the enzyme in covalent catalysis?
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What is the primary concept behind the induced fit model of enzyme-substrate binding?
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What is the primary function of isoenzymes?
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Why are isoenzymes important in developmental and metabolic processes?
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How do researchers typically detect and quantify enzymes in cells?
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What is the basis for calculating enzyme concentration in cells?
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What is the significance of the induced fit model in understanding enzyme-substrate interactions?
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What is a key characteristic of isoenzymes that distinguishes them from one another?
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What is the purpose of assaying the catalytic activity of enzymes in research and clinical laboratories?
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Study Notes
Enzymes and Their Applications
- Enzymes are biocatalysts synthesized by living cells, and they are protein in nature except for ribozymes, which are RNA in nature.
- Enzymes are colloidal, thermolabile, and specific in their action.
- Examples of enzymes and their applications include:
- Rennin, used in the production of cheese.
- Lactase, used to remove lactose from milk for lactose-intolerant individuals.
- Stereospecific enzyme catalysts, used in the biosynthesis of complex drugs or antibiotics.
The Nature of Enzymes
- Enzymes are globular proteins with at least tertiary structure, capable of binding substrate molecules to a part of their surface.
- Enzymes catalyze the conversion of one or more compounds (substrates) into one or more different compounds (products).
- Enzymes enhance the rates of the corresponding non-catalyzed reaction by factors of 10^16 or more.
- Enzymes are neither consumed nor permanently altered as a consequence of their participation in a reaction.
- Enzymes are specific not only for the type of reaction catalyzed but also for a single substrate or a small set of closely related substrates.
- Enzymes are stereospecific catalysts that typically catalyze reactions of only one stereoisomer of a given compound.
Enzymes Nomenclature and Classification
- The early discovered enzymes were designated by appending the suffix –ase to a descriptor for the type of reaction catalyzed.
- Enzymes can be classified into six classes according to the International Union of Biochemistry (IUB) system:
- Oxidoreductases: enzymes that catalyze oxidations and reductions.
- Transferases: enzymes that catalyze the transfer of moieties such as glycosyl, methyl, or phosphoryl groups.
- Hydrolases: enzymes that catalyze hydrolytic cleavage of C-C, C-O, C-N, and other covalent bonds.
- Lyases: enzymes that catalyze non-hydrolytic cleavage of C-C, C-O, C-N, and other covalent bonds by atom (functional group) elimination, generating double bonds.
- Isomerases: enzymes that catalyze geometric or structural changes within a molecule.
- Ligases: enzymes that catalyze the joining together (ligation) of two molecules in reactions coupled to the hydrolysis of ATP.
Enzymes Mechanisms to Facilitate Catalysis
- Enzymes use combinations of four general mechanisms to achieve dramatic enhancements of the rates of chemical reactions:
- Catalysis by proximity: the higher concentration of substrate molecules at the active site leads to a greater rate of reaction.
- Acid-base catalysis: enzymes can contribute to catalysis by acting as acids or bases.
- Catalysis by strain: enzymes bind their substrates in a conformation that is somewhat unfavorable for the bond targeted for cleavage, resulting in a strained conformation.
- Covalent catalysis: the process of covalent catalysis involves the formation of a covalent bond between the enzyme and one or more substrates.
Enzyme-Substrate Interaction Models
- Two models have been proposed to explain how an enzyme binds its substrate:
- Lock and key model: an old model that accounted for the specificity of enzyme-substrate interactions but failed to account for the dynamic changes that accompany substrate binding and catalysis.
- Induced fit model: a model that states that when substrates approach and bind to an enzyme, they induce a conformational change that is analogous to placing a hand (substrate) into a glove (enzyme).
Isoenzymes
- Isoenzymes are physically distinct versions of a given enzyme, each of which catalyzes the same reaction.
- Isoenzymes are produced by different genes and are not redundant despite their similar functions.
- Isoenzymes may have different substrates, and they may also possess differences in properties such as sensitivity to particular regulatory factors or substrate affinity.
Detection of Enzymes
- The relatively small quantities of enzymes present in cells hinder determination of their presence and concentration.
- However, enzymes' ability to rapidly transform thousands of molecules of a specific substrate into products has enabled their detection and quantification.
- Assays of the catalytic activity of enzymes are frequently used in research and clinical laboratories.
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Description
Learn about the importance of enzymes in various industries, such as cheese production and lactose removal, and their role in biosynthesis. Understand the nature of enzymes and their characteristics.
