Enzymes and Their Functions

Enzymes

• Biocatalysts that accelerate chemical reactions without being consumed
• Colloidal and thermolabile
• Soluble in nature

Chemical Nature

• Mostly proteins, 3D structure
• Exceptions like ribozymes, which are RNA

Ribozymes

• RNA molecules with catalytic activity,
• Found in RNA metabolism, like splicing
• Ribonuclease P (RNAse H) cleaves RNA in DNA/RNA hybrids
• Peptidyltransferase forms peptide bonds in protein synthesis

Abzymes

• Antibodies with catalytic activity

Simple Enzymes

• Composed of only amino acids
• Examples include urease, trypsin, pepsin, aldolase, and arginase

Conjugated Proteins

• Protein part (apoenzyme) + non-protein part (prosthetic group, cofactor, or coenzyme)

Multienzyme Complexes

• Formed by the association of more than one enzyme
• Examples include pyruvate dehydrogenase and fatty acid synthase complexes

Highly Organized Enzyme Systems

• Examples include electron transport chain enzymes

Substrate and Products

• Substrate: The compound on which the enzyme acts
• Product: The compound produced by the enzyme acting on the substrate

Enzyme Specificity

• Enzymes act on specific substrates or types of reactions
• Subtypes include:
  • Group or broad specificity: Acts on a group of related structures (e.g., hexokinase)
  • Absolute specificity: Acts on a particular substrate (e.g., glucokinase)
  • Stereospecificity: Acts on only one isomer of a substrate (e.g., amylase)

Reaction Specificity

• Catalyze only one type of reaction for a given substrate
• Examples include pyruvate dehydrogenase, alanine aminotransferase, pyruvate carboxylase, and others

Enzyme Regulation

• Regulation of changes in catalytic activity of enzyme in response to cellular needs
• Regulation of enzyme concentration (synthesis and degradation)

Enzyme Location

• Located in specific compartments within cells (e.g., cytoplasm, mitochondria, nucleus).

Enzyme Classification

• Classified by the International Union of Biochemistry and Molecular Biology (IUBMB)

Enzyme Nomenclature

• Enzyme Commission (EC) numbers assigned to enzymes
• Each enzyme has a unique 4-digit code
• First digit indicates major class (e.g., oxidoreductase)

Catalytic Efficiency

• Enzymes catalyze reactions at rates 10^3 to 10^17 times faster than uncatalyzed reactions
• They do not alter the equilibrium constant of the reaction
• Active site: A small region of the enzyme where the substrate binds and the catalytic reaction occurs

Active Site

• Active site is the region of an enzyme that binds substrate molecule(s) during the facilitation of the catalytic reaction.
• Its precise shape and functionality is crucial for enzyme specificity.

Mechanisms of Enzyme-Catalyzed Reactions

• Enzyme-substrate complex formation
• Transition state complex formation
• Product formation
• Release of product

Factors Affecting Enzyme Activity

• Enzyme concentration
• Substrate concentration
• pH
• Temperature
• Product concentration
• Cofactors/coenzymes
• Inhibitors

Enzyme Inhibitors

• Substances that decrease the rate of an enzyme-catalyzed reaction.
• Types include:
  • Reversible inhibitors (competitive, non-competitive, uncompetitive)
  • Irreversible inhibitors

Competitive Inhibition

• Inhibitor has structural similarity to substrate
• Competes with substrate for binding at active site
• Increasing substrate concentration can overcome inhibition
• Km increases, Vmax is unchanged

Noncompetitive Inhibition

• Inhibitor has no structural similarity with substrate
• Binds to enzyme at a site other than the active site
• Altering enzyme conformation
• Km is unchanged, Vmax decreases

Mixed Inhibition

• Mixed type of inhibition
• Both reversible and irreversible
• Inhibitor binds to both free enzyme and ES complex

Irreversible Inhibition

• Inhibitor forms a covalent bond with the active site
• Usually toxic

Cofactors and Coenzymes

• Inorganic or organic non-protein components that aid enzyme function
• Coenzymes are organic cofactors
• Frequently derived from vitamins
• Important in electron transfer, group transfer, and other reactions
• Most enzymes require cofactors to function optimally

Explore the fascinating world of enzymes in this quiz. Learn about their chemical nature, types, and functions including ribozymes and abzymes. Test your knowledge on simple enzymes, conjugated proteins, and multienzyme complexes.