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Questions and Answers
What is the primary function of an enzyme?
Which statement about enzymes is true?
What does the induced-fit model describe about enzyme activity?
Which type of enzyme is responsible for hydrolysis reactions?
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What term describes the non-protein part of an enzyme necessary for its function?
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In competitive inhibition, how does the inhibitor affect enzyme function?
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What is the role of amino acids in the active site of enzymes?
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Which of the following describes an isomerase?
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What characterizes noncompetitive inhibition?
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What does the active site of an enzyme do?
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Which process involves the product of an enzyme-catalyzed reaction inhibiting an earlier reaction?
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Which of these is NOT a major group of enzymes?
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Which of the following enzymes specifically catalyzes peptide bonds formed by the carboxyl groups of Lys and Arg?
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Which amino acid is NOT among the five most important in enzyme active sites?
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What is a proenzyme (zymogen)?
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How do enzymes affect activation energy in chemical reactions?
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What is the role of a competitive inhibitor in enzyme activity?
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Which factor does NOT affect the rate of an enzyme-catalyzed reaction?
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In which scenario would a noncompetitive inhibitor be effective?
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What happens to enzyme activity as substrate concentration increases?
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Which of the following best describes the lock-and-key model of enzyme action?
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How does temperature generally affect enzyme activity?
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What defines an enzyme's active site?
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How does pH influence enzyme activity?
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What happens to trypsinogen to activate it?
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What term describes an enzyme that is regulated by a change occurring at a site other than its active site?
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Which of the following describes negative modulation in allosteric enzymes?
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Which of the following is an example of protein modification affecting enzyme activity?
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What is an isoenzyme?
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Which forms of lactate dehydrogenase predominately exist in specific tissues?
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What is the result of binding a positive modulator to an allosteric enzyme?
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What is the role of a regulator in allosteric enzymes?
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Study Notes
Enzyme Catalysis
- Enzymes are biological catalysts.
- Enzymes are mostly proteins, with the exception of some RNA molecules that catalyze self-cleavage.
- Enzymes can increase the rate of a reaction by a factor of 10^9 to 10^20.
- Some enzymes catalyze the reaction of only one compound.
- Some enzymes are stereospecific.
- Some enzymes catalyze reactions of specific types of compounds or bonds.
Classification of Enzymes
- Enzymes are commonly named after the reaction or reactions they catalyze.
- Enzymes are classified into six major groups:
- Oxidoreductases: oxidation-reduction reactions.
- Transferases: group transfer reactions.
- Hydrolases: hydrolysis reactions.
- Lyases: addition of groups to a double bond, or removal of groups to create a double bond.
- Isomerases: isomerization reactions.
- Ligases: the joining of two molecules.
Terms in Enzyme Chemistry
- Apoenzyme: the protein part of an enzyme.
- Cofactor: a nonprotein portion of an enzyme that is necessary for catalytic function, like metallic ions.
- Coenzyme: a nonprotein organic molecule that acts as a cofactor, often a B vitamin.
- Substrate: the compound or compounds whose reaction an enzyme catalyzes.
- Active site: the specific portion of the enzyme to which a substrate binds during reaction.
Terms in Enzyme Chemistry (Continued)
- Activation: any process that initiates or increases the activity of an enzyme.
- Inhibition: any process that makes an active enzyme less active or inactive.
- Competitive inhibitor: any substance that binds to the active site of an enzyme thereby preventing binding of substrate.
- Noncompetitive inhibitor: any substance that binds to a portion of the enzyme other than the active site and thereby inhibits the activity of the enzyme.
Enzyme Activity
- Enzyme activity is a measure of how much a reaction rate is increased.
- How much an enzyme activity is influenced by:
- Enzyme concentration
- Substrate concentration
- Temperature
- pH
Lock-and-key Model
- The enzyme is a rigid three-dimensional body.
- The enzyme surface contains the active site.
Induced-fit Model
- The active site becomes modified to accommodate the substrate.
Mechanism of Action
- Both the lock-and-key model and the induced-fit model emphasize the shape of the active site.
- The most important factor is the chemistry of the active site.
- Five amino acids participate in the active sites of more than 65% of enzymes.
Catalytic Power
- Enzymes provide an alternative pathway for reaction with a lower activation energy.
- This results in a faster rate.
Enzyme Regulation
- Feedback control: an enzyme-regulation process where the product of a series of enzyme-catalyzed reactions inhibits an earlier reaction in the sequence.
Enzyme Regulation (Continued)
- Proenzyme (zymogen): an inactive form of an enzyme that must have part of its polypeptide chain hydrolyzed and removed before it becomes active.
Enzyme Regulation (Continued)
- Trypsin, a digestive enzyme, is an example of a proenzyme.
- Trypsinogen is initially inactive.
- It becomes active after a six-amino acid fragment is hydrolyzed and removed from its N-terminal end.
- This removal changes the primary and tertiary structure, allowing the molecule to become active.
Enzyme Regulation (Continued)
- Allosterism: enzyme regulation based on an event occurring at a place other than the active site that creates a change in the active site.
- Allosteric enzyme: An enzyme regulated by this mechanism.
- Negative modulation: inhibition of an allosteric enzyme.
- Positive modulation: stimulation of an allosteric enzyme.
- Regulator: a substance that binds to an allosteric enzyme.
Enzyme Regulation (Continued)
- Protein modification: the process of affecting enzyme activity by covalently modifying it.
- Phosphorylation/dephosphorylation: a common example.
- Pyruvate kinase (PK) is active.
- Phosphorylation inactivates the enzyme to pyruvate kinase phosphate (PKP).
Enzyme Regulation (Continued)
- Isoenzyme: an enzyme that occurs in multiple forms, each catalyzing the same reaction.
- Lactate dehydrogenase (LDH) is an example.
- LDH catalyzes the oxidation of lactate to pyruvate.
- The enzyme is a tetramer of H and M chains.
- H4 is predominantly in heart muscle.
- M4 is predominantly in the liver and skeletal muscle.
- H3M, H2M2, and HM3 also exist.
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Description
Test your knowledge on enzyme catalysis and classification with this engaging quiz. Explore the various types of enzymes, their functions, and key terms related to enzyme chemistry. Challenge yourself and deepen your understanding of these essential biological catalysts.
