Biochemistry Topics   

Enzymes

Enzyme Basics

A catalyst is a substance that accelerates a reaction without being consumed by it. Enzymes are catalysts that alter and regulate the rate a chemical reaction in a biological system. Most enzymes are proteins, but some are RNA.  The six major enzyme classes are:

• Oxydoreductases transfer electrons as either hydride ions or as H atoms (examples: dehydrogenases, oxidases, reductases, peroxidases, catalyses, oxygenases, hydrolases)
  
  
• Transferases catalyze group-transfer reactions (examples: transaldolase, transketolase, acyl-, methyl, glucosyl, and phosphoryl-transferases, kinases, phosphomutases)
  
  
• Hydrolases catalyze hydrolysis reactions, i.e. the transfer of functional groups to water (examples: esterases, glycosidases, peptidases, phosphatases, thiolases, phospholipases, amidases, deamidases, ribonucleases)
  
  
• Lyases catalyze the addition of groups to double bonds or formation of double bonds by removal of groups (examples: decarboxylases, aldolases, hydratases, dehydratases, synthases)
  
  
• Isomerases transfer groups within a molecule to yield isomeric forms (examples: racemases, epimerases, isomerases, mutases)
  
  
• Ligases catalyze the formation of C-C, C-S, C-O and C-N bonds by condensation reactions coupled to ATP cleavage (examples: synthetases, carboxylases)

The reactant that interacts with a specific enzyme is its substrate. The conversion of a substrate to product occurs in the active site of the enzyme. The active site makes a relatively small part of the total volume on the enzyme, and its groups can come from different parts of the amino acid sequence because of 3-dimensional folding. Substrates are bound in clefts or crevices by electrostatic and hydrogen bonds, Van der Waals forces, and hydrophilic interactions. Substrate specificity is defined by complementary substrate and active site structures.

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Advance Topics: Cellular and Molecular Biology
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Coenzymes

Coenzymes are small molecules required for catalytic activity of some enzymes. Complete topic not yet available.

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Kinetics

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Mechanisms

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Regulation

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