Podcast
Questions and Answers
Which of the following best describes the initial step in enzyme catalysis?
Which of the following best describes the initial step in enzyme catalysis?
What role do coenzymes typically play in enzyme function?
What role do coenzymes typically play in enzyme function?
Which class of enzymes is primarily responsible for catalyzing the addition or removal of hydrogen atoms?
Which class of enzymes is primarily responsible for catalyzing the addition or removal of hydrogen atoms?
In the classification of enzymes, what does the four-digit number assigned to each enzyme signify?
In the classification of enzymes, what does the four-digit number assigned to each enzyme signify?
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Which of the following is NOT one of the six functional classes of enzymes according to the International Union of Biochemists?
Which of the following is NOT one of the six functional classes of enzymes according to the International Union of Biochemists?
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The formation of the enzyme-substrate complex (ES) leads to which transitional state during enzyme catalysis?
The formation of the enzyme-substrate complex (ES) leads to which transitional state during enzyme catalysis?
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What defines the trivial name of an enzyme as commonly used in everyday language?
What defines the trivial name of an enzyme as commonly used in everyday language?
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Which of the following best describes lyases as a class of enzymes?
Which of the following best describes lyases as a class of enzymes?
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Which step follows the formation of the enzyme-substrate complex in the enzyme catalysis process?
Which step follows the formation of the enzyme-substrate complex in the enzyme catalysis process?
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How are enzymes that catalyze isomerizations uniquely categorized?
How are enzymes that catalyze isomerizations uniquely categorized?
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What term is used for enzymes that are wholly composed of protein?
What term is used for enzymes that are wholly composed of protein?
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Which component of a holoenzyme is specifically the protein part?
Which component of a holoenzyme is specifically the protein part?
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What type of enzyme requires a metal ion as part of its composition?
What type of enzyme requires a metal ion as part of its composition?
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Which of the following statements about coenzymes is true?
Which of the following statements about coenzymes is true?
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What defines the specificity of enzymes towards substrates?
What defines the specificity of enzymes towards substrates?
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In what way do isozymes differ from one another?
In what way do isozymes differ from one another?
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Which of the following statements is true regarding the cytochrome coenzymes?
Which of the following statements is true regarding the cytochrome coenzymes?
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Which enzyme is best known for having multiple isozymes?
Which enzyme is best known for having multiple isozymes?
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What is the role of phosphate groups in coenzymes like pyridoxal phosphate?
What is the role of phosphate groups in coenzymes like pyridoxal phosphate?
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Which of the following best describes racemases?
Which of the following best describes racemases?
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Study Notes
Enzymes 1
- Enzymes are biological catalysts
- Almost all life processes rely on enzyme activity
- Almost all enzymes are proteins, except for ribozymes (RNA modifying catalysts)
- In enzyme-catalyzed reactions, substrate concentrations are typically higher than enzyme concentrations
- Enzyme catalysis involves substrate binding to a specific site on the enzyme (active or catalytic site)
- During enzyme catalysis, the ES complex forms, transitions to ES*, and then to the EP complex before dissociating into product and free enzyme.
- Enzyme reactions follow this series: E + S <=> ES <=> ES* <=> EP <=> E + P
- Initially, enzymes were named arbitrarily by their discoverers
- As knowledge expanded, enzyme classification systems became more complex
- Currently, enzymes are grouped into 6 classes by the International Union of Biochemists (IUB)
- The IUB assigns a unique number to each enzyme and a textual name
- Enzyme classification is based on the type of chemical reaction catalyzed
IUB Enzyme Classifications
- Oxidoreductases: Add or remove hydrogen atoms
- Transferases: Transfer functional groups
- Hydrolases: Add water across a bond, hydrolyzing it
- Lyases: Add or remove water, ammonia, or carbon dioxide across double bonds
- Isomerases: Catalyze isomerizations
- Ligases: Join two chemical groups using energy from ATP
Enzyme Nomenclature
- Each enzyme is given a four-digit number specifying its class, subclass, substrate, and reaction type
- Enzyme names combine the substrate name, product name, and functional class
- In everyday use, enzymes are often called by their common (trivial) names.
Enzyme Composition
- Enzymes are also classified by their composition
- Simple enzymes are composed entirely of protein
- Complex enzymes are composed of protein plus a small organic molecule (cofactor)
- Complex enzymes are also known as holoenzymes
Coenzymes
- Coenzymes act as transporters of chemical groups between reactants.
- Chemical groups carried by coenzymes can vary in complexity
- e.g., hydride ion (H+ + 2e-), a molecule of hydrogen, or an amine group (-NH2)
- Coenzymes are chemically changed during enzyme action, thus they can be considered "second substrates"
- Coenzymes are recycled to their original form after donating a chemical group to an acceptor molecule.
Enzyme Specificity
- Enzymes are highly specific for the type of reaction they catalyze
- Enzymes are substrate specific
- Some enzymes exhibit broad substrate specificity (e.g., alcohol dehydrogenase and hexokinase).
- Enzymes are generally specific for a particular steric configuration (D or L optical isomers) of a substrate
- Racemases are an exception; they convert D isomers to L isomers and vice-versa.
Isozymes
- Isozymes are multiple forms of an enzyme that work on the same substrate and produce the same product.
- Isozymes result from slight variations in the genes.
- Various isozymes are expressed in different tissues of the body -Example: Lactic dehydrogenase (LDH) is a tetrameric enzyme composed of two types of protein subunits (H and M) in different arrangements
- Different subunit arrangements produce different isozymes, each with a specific tissue distribution -Example: HHHH (Heart-type), HHHM, HHMM, HMMM, MMMM (Muscle-type) - LDH isozymes are widely used clinically as markers of tissue damage.
Enzyme-Substrate Interactions
- Two models explain enzyme-substrate binding:
- Key and lock model
- Induced fit model
- The induced fit model proposes that the initial enzyme-substrate interaction is weak and possibly not completely complementary but it induces conformational changes in the enzyme
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Description
This quiz covers the essential concepts of enzymes as biological catalysts crucial for various life processes. You'll learn about enzyme classification, mechanisms of action, and the formation of enzyme-substrate complexes. Test your knowledge on how enzymes function and their importance in biochemical reactions.
