Overview
This lecture covers the role of enzymes in catalyzing biochemical reactions, how enzyme names reflect their functions, and the six major classes of enzyme-catalyzed reactions.
Enzyme Function and Naming
- Enzymes increase reaction rates by lowering activation energy.
- Enzyme names usually end with "ase" and describe their substrate or reaction.
- Examples: DNA polymerase synthesizes DNA; hexokinase adds phosphate to six-carbon sugars.
The Six Major Enzyme Classes
1. Transferases
- Transferases move functional groups from one molecule (B) to another (A).
- Example: Peptidyl transferase transfers amino acids to growing peptide chains during protein synthesis.
2. Ligases
- Ligases join two molecules (A and B) to form a single complex (AB).
- Example: DNA ligase joins DNA strands in replication.
3. Oxidoreductases
- Oxidoreductases catalyze electron transfer between molecules (oxidation and reduction).
- Oxidases remove electrons; reductases add electrons.
- Example: Lactate dehydrogenase removes hydrides (electrons) in lactic acid fermentation.
4. Isomerases
- Isomerases convert a molecule into one of its isomers.
- Example: Phosphoglucose isomerase converts glucose-6-phosphate to fructose-6-phosphate in glycolysis.
5. Hydrolases
- Hydrolases break bonds in molecules using water, splitting them into two products.
- Example: Serine hydrolases (proteases) break peptide bonds in proteins.
6. Lyases
- Lyases break bonds in molecules without using water or oxidation/reduction.
- Example: Argininosuccinate lyase cleaves argininosuccinate into arginine and succinate during the urea cycle.
- Lyases often create double bonds or ring structures.
Key Terms & Definitions
- Enzyme — protein that accelerates chemical reactions by lowering activation energy.
- Activation Energy — minimum energy required to start a reaction.
- Transferase — enzyme transferring functional groups between molecules.
- Ligase — enzyme joining two molecules together.
- Oxidoreductase — enzyme facilitating oxidation-reduction (electron transfer) reactions.
- Isomerase — enzyme converting a molecule to an isomer.
- Hydrolase — enzyme breaking bonds via water (hydrolysis).
- Lyase — enzyme breaking bonds without hydrolysis or oxidation.
Action Items / Next Steps
- Review glycolysis and DNA replication steps for examples of enzyme reactions.
- Study the names and functions of enzymes in each of the six major classes.