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In the name of Allah, the most Beneficent and the most Merciful. Lecture 2. Enzymes Special proteins that act as biological catalysts. Enzymes are not changed or consumed by the reaction !. Substrate The chemical that undergoes an enzyme-catalyze reaction is known as substrate.
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In the name of Allah, the most Beneficent and the most Merciful
EnzymesSpecial proteins that act as biological catalysts. Enzymes are not changed or consumed by the reaction! Substrate The chemical that undergoes an enzyme-catalyze reaction is known as substrate. Enzyme substrate complex (ES) Enzyme-bound product (EP)
Activation energy: energy to start a reaction. Requires energy input to break bonds
Active site Hollow surface or cleft on the enzyme to which the substrate must fit like a lock and key.
Active site changes shape in order to accommodate the substrate and to maximize the binding forces b/w the substrate and the active site
Induced fit:enzyme changes shape of active site so substrate fits perfectly. This allows some enzymes to catalyze several different reactions
Nucleophile enzymes Acid/Base catalyst enzyme Catalytic mechanism of Amino acids They can aid the mechanism by acting as
Definition Enzyme inhibitors are molecules that interact in some way with the enzyme to prevent it from working in the normal manner They inhibit the catalytic activity of an enzyme. Types of inhibitors 1- Specific 2- nonspecific, 3-irreversible, 4-reversible 5-competitive 6-noncompetitive. Poisons and drugs Enzyme Inhibitors
Acids and Bases: Enzyme activity is also controlled by pH. As the pH is decreased or increased, the nature of the various acid and amine groups on side chains is altered with resulting changes in the overall shape structure of the enzyme. Temperature: Usually, the reaction rate increases with temperature, but with enzyme reactions, a point is reached when the reaction rate decreases with increasing temperature. At high temperatures the protein part of the enzyme begins to denature, thus inhibiting the reaction. Nonspecific Inhibitors:A nonspecific inhibition effects all enzymes in the same way. Non-specific methods of inhibition include any physical or chemical changes which ultimately denatures the protein portion of the enzyme and are therefore irreversible
Specific Inhibitors: Specific Inhibitors exert their effects upon a single enzyme. Most poisons work by specific inhibition of enzymes. Many drugs also work by inhibiting enzymes in bacteria, viruses, or cancerous cells Competitive Inhibitors: A competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate. The inhibitor competes for the same active site as the substrate molecule. The inhibitor may interact with the enzyme at the active site, but no reaction takes place. The inhibitor is "stuck" on the enzyme and prevents any substrate molecules from reacting with the enzyme. However, a competitive inhibition is usually reversible if sufficient substrate molecules are available to ultimately displace the inhibitor. Therefore, the amount of enzyme inhibition depends upon the inhibitor concentration, substrate concentration, and the relative affinities of the inhibitor and substrate for the active site.
Greater the concentration of natural substrate the less efficient is the inhibitor.
Noncompetitive inhibitor They do not compete with natural substrate for active site. They bind to different region of enzyme in order to produce an induced fit Thus active site is no longer recognizable to the substrate. Allosteric site The binding site used by a noncompetitive inhibitor is called an allosteric site. Explanation from text.
Reversible inhibitors They interact with enzymes through non covalent intermolecular interactions (H-bonding, ionic interaction, van der Waals interactiob) Irreversible inhibitors They contain electrophilic groups which are susceptible to attack from Nu amino gp. present in enzyme resulting in formation of covalent bond. Competitive or noncompetitive inhibitors can bereversible or non reversible
Factors affecting enzymes activity a) Temperature: Disrupts hydrogen bonds, alters protein shape (denature) b) pHhydrogen ion concentration disrupts bonds between amino : acidsc). Substrate Concentration: Increased substrate concentration increases reaction rate until all enzymes are involved, then reactions level outd) Enzyme Concentration: Increased enzyme concentration increases reaction rate until all substrate is used up, then reactions decrease.
Biochemical PathwaysSeveral to many enzymes are placed side by side on membranes within cells, each enzyme completing one of the many steps to convert 1 substance into another. ("Assembly Line")
