24 Questions
What is the basis for the classification of enzymes in the EC system?
The nature of the chemical reactions they catalyze
Which of the following is an example of an enzyme name based on the nature of the reaction?
Oxidase
What is the purpose of the EC classification system?
To provide a universal system for enzyme classification and naming
What is the first number in an EC classification number?
The class of the enzyme
What is the function of oxidoreductases?
To catalyze oxido-reductions
What is the basis for naming enzymes in the IUB system?
The nature of the chemical reaction they catalyze
What is the common name for oxidoreductases wherever possible?
Dehydrogenase
What is the prefix for EC classification numbers?
EC
What is the primary function of transferases?
To transfer a group from one compound to another
What is the naming convention for transferases?
Acceptor grouptransferase or donor grouptransferase
What is the classification number for hydrolases?
EC 3
What is unique about the naming convention of hydrolases?
Their names are formed by the name of the substrate with the suffix -ase
What is the primary function of lyases?
To cleave C-C, C-O, C-N and other bonds by means other than by hydrolysis or oxidation
What is the naming convention for lyases?
Substrate group-lyase
What is the term used for lyases that eliminate water?
Dehydratase
What is the term used in the name of lyases when the reverse reaction is more important?
Synthase
What type of reaction do Oxidoreductases catalyze?
Transfer of electrons
Which enzyme class is responsible for the formation of C—C, C—S, C—O, and C—N bonds?
Ligases
What is the name of the enzyme class that catalyzes the movement of ions or molecules across membranes or their separation within membranes?
Translocases
What is the typical naming convention for enzymes that catalyze the joining of two molecules with concomitant hydrolysis of the diphosphate bond in ATP or a similar triphosphate?
Ligase or Synthase
Which enzyme class catalyzes the transfer of groups within molecules to yield isomeric forms?
Isomerases
What is the purpose of the EC classification system?
To classify enzymes based on the type of reaction they catalyze
What type of reaction do Hydrolases catalyze?
Hydrolysis
Which enzyme class is responsible for the transfer of groups from one molecule to another?
Transferases
Study Notes
Enzyme Nomenclature
- Enzyme nomenclature in the early 20th century lacked consistency, leading to inconsistencies in naming conventions.
Inconsistencies in Nomenclature
- Four systems of nomenclature were used, including:
- Combining "ase" with the substrate name (e.g., amylase, urease)
- Combining "ase" with the end product name (e.g., alcoholase, glucose)
- Based on the nature of the reaction (e.g., oxidase, reductase, invertase)
- Using terms with no connection to the process (e.g., zymase, pepsin, trypsin)
EC Scheme for Classification
- Enzymes are classified and named based on the chemical reactions they catalyze.
- The EC scheme uses a four-part classification number (e.g., aconitate hydratase EC 4.2.1.3).
- The four parts of the classification number indicate:
- Class (e.g., oxidoreductases)
- Subclass
- Sub-subclass
- Serial number in sub-subclass
Enzyme Classes
-
There are six major classes of enzymatic reactions:
EC 1: Oxidoreductases
- Catalyze oxido-reductions
- Substrate oxidized is regarded as a hydrogen or electron donor
- Classification based on 'donor:acceptor oxidoreductase'
EC 2: Transferases
- Catalyze group transfer reactions
- Classification based on 'donor:acceptor grouptransferase'
EC 3: Hydrolases
- Catalyze hydrolysis reactions
- Classification based on 'substrate hydrolase'
EC 4: Lyases
- Catalyze cleavage of C-C, C-O, C-N, and other bonds
- Classification based on 'substrate group-lyase'
EC 5: Isomerases
- Catalyze changes within a single molecule
EC 6: Ligases
- Catalyze joining of two molecules with concomitant hydrolysis of ATP or similar triphosphate
EC 7: Translocases
- Catalyze movement of ions or molecules across membranes or their separation within membranes
Learn about the history of enzyme nomenclature, including the early 20th century developments, inconsistencies, and the role of IUB and the Enzyme Commission. Discover the four systems of nomenclature and their applications.
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