Enzymes and Their Properties

Enzymes

• Enzymes are biologically active proteins that speed up the breakdown of food.
• Enzymes are biological catalysts; they accelerate reactions without being consumed or altered.
• Enzymes are involved in crucial life processes, including DNA replication, transcription, protein synthesis, metabolism, and signal transduction.

Enzyme Classification and Properties

• The provided document lists topics to be learned including classification of enzymes, their properties, holoenzymes, apoenzymes, cofactors, coenzymes, mechanisms of enzyme action, kinetics of chemical reactions, and factors affecting enzyme activity (substrate concentration, pH, temperature).
• These topics, along with enzyme classes (Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases) are part of a comprehensive study of enzymes.

Active Site

• Enzyme molecules have an active site, a pocket or cleft where substrates bind.
• The active site's shape is crucial for substrate recognition.
• Active sites contain amino acid residues that participate in substrate binding and catalysis.
• Substrate binding to the enzyme forms an enzyme-substrate complex.

Substrate-Binding Sites

• Enzyme specificity, the ability of an enzyme to react with a particular substrate, arises from the precise 3D arrangement of amino acids in the active site.
• The "lock-and-key" and "induced-fit" models describe how substrates bind to enzymes.

Enzyme-Substrate Models

• Enzymes can be flexible.
• After substrate binding, the enzyme's structure changes to create a stable enzyme-substrate complex.
• The binding site of the enzyme is rigid, accommodating only substrates of the correct shape.

Cofactors and Coenzymes

• Many enzymes require cofactors (non-protein helper molecules) for optimal activity.
• Cofactors can be temporary (bound by ionic or hydrogen bonds) or permanent (bound by covalent bonds).
• Coenzymes are a subset of cofactors. They are organic molecules often derived from vitamins.
• Enzymes with bound coenzymes are termed holoenzymes, while enzymes without are apoenzymes.

Factors Affecting Enzyme Reaction Velocity

• Substrate Concentration: Reaction velocity increases with substrate concentration until the enzyme becomes saturated.
• Temperature: Reaction velocity increases with temperature until a peak, then decreases due to enzyme denaturation.
• pH: The concentration of protons ([H+]) affects reaction velocity. Extreme pH values can lead to enzyme denaturation.

Isoenzymes

• Isoenzymes are enzymes that catalyze the same reaction but differ in amino acid sequence.
• Tissues contain specific isoenzymes or combinations.
• Isozyme levels in the blood can indicate tissue damage (e.g., heart attack)

Michaelis-Menten kinetics

• Vmax is the maximum reaction velocity.
• Km is the Michaelis constant, reflecting the affinity of the enzyme for its substrate.
• A small Km indicates high affinity, while a large Km indicates low affinity.