Enzymes

• Enzyme inhibitors can either decrease or completely stop the activity of enzymes.
• A spontaneous reaction is a chemical or physical reaction that will occur without an input of energy
• To determine if a reaction is spontaneous, consider the change in energy content of a system and its change in entropy
• Free energy (G) is the portion of a system's energy available to do work
• The formula to calculate the change in free energy (ΔG) for any chemical reaction is: ΔG = ΔH - TΔS
• For a reaction to be spontaneous, ΔG must be negative
• In reversible reactions, ΔG is near zero and can be adjusted by changing the concentration of products and reactants
• Living organisms constantly take in energy-rich molecules to do work, keeping ΔG negative
• Exergonic reactions release free energy, with products containing less free energy than reactants
• Endergonic reactions require energy from the surroundings, with products containing more free energy than reactants
• In metabolic pathways, energy is released in catabolic reactions and used in anabolic reactions
• ATP is the chief energy currency of the cell, used to drive endergonic reactions
• The breakdown of ATP through hydrolysis results in the formation of ADP and inorganic phosphate (Pi)
• Energy coupling involves transferring the terminal phosphate group of ATP to a reactant molecule in an endergonic reaction
• The ATP/ADP cycle involves the continual hydrolysis and resynthesis of ATP, using energy from the breakdown of carbohydrates, proteins, and fats
• Oxidation-reduction reactions involve the transfer of energy through biological systems, with electrons carrying energy as they pass from one atom to another
• Enzymes are biological catalysts that lower activation energy, accelerating reaction rates without altering the ΔG of the reaction
• Enzymes are proteins that carry out most catalysis in living organisms

  
• Enzymes reduce activation energy and are biological catalysts
• Enzymes stabilize the transition state through mechanisms like bringing reacting molecules together and exposing them to altered charge environments
• Enzymes have unique three-dimensional shapes that enable them to stabilize a temporary association between substrates
• In enzymatic reactions, an enzyme combines briefly with reacting molecules and is released unchanged when the reaction is complete
• The reactant that an enzyme acts on is called the substrate
• Each type of enzyme catalyzes the reaction of a single type of substrate molecule or group of closely related molecules (enzyme specificity)
• The substrate interacts with a small pocket or groove in the enzyme molecule, called the active site
• When the substrate binds at the active site, both enzyme and substrate molecules are distorted, making the chemical bonds in the substrate ready for reaction (induced fit)
• Once an enzyme-substrate complex is formed, catalysis occurs and the substrate is converted into one or more products
• Many enzymes require a cofactor, a nonprotein group that binds to the enzyme, for catalytic activity
• Some cofactors are metallic ions like iron, copper, magnesium, zinc, and manganese
• Other cofactors are small organic molecules (coenzymes) often derived from vitamins
• Enzymes can be regulated by competitive and noncompetitive inhibition, allosteric regulation, and covalent modification of enzyme structure
• Enzyme inhibitors are nonsubstrate molecules that bind to an enzyme and decrease its activity
• In allosteric regulation, enzyme activity is controlled by the reversible binding of a regulatory molecule to the allosteric site, a location on the enzyme outside the active site
• Enzymes are regulated by chemical linkage to ions, functional groups, or other molecules that induce changes in the enzyme's activity
• Temperature affects all proteins, including enzymes, as kinetic motion increases with temperature, eventually leading to enzyme denaturation
• The earliest forms of life might have inhabited an "RNA world" where ribozymes acted as both enzymes and informational molecules
• Non-competitive enzyme inhibition involves binding of the inhibitor at another location on the enzyme, which changes its shape so that the substrate cannot fit into the active site anymore.
• Competitive enzyme inhibition occurs when the substrate is bound to the active site, but an inhibitor molecule binds to it instead.
• Coenzymes are non-protein cofactors that are essential for the activity of enzymes.
• Enzyme inhibitors can be competitive or non-competitive.