Enzymes Class 5 - PDF

Enzymes  Enzymes There are two fundamental conditions for life 1. The organism must be able to self replicate 2. It must be able to catalyze chemical reactions efficiently and selectively The molecules which catalyze chemical reactions were given name...

Enzymes  Enzymes There are two fundamental conditions for life 1. The organism must be able to self replicate 2. It must be able to catalyze chemical reactions efficiently and selectively The molecules which catalyze chemical reactions were given name as enzymes by Frederick W. Kühne Enzymes are reaction catalyst of biological systems. They are central to every biochemical process. They are acting in organized sequences and catalyze the hundreds of stepwise reactions  Properties of enzymes Most biological catalysts are proteins called enzymes. Certain RNA molecules called ribozymes are also catalysts. Enzymes have molecular weights ranging from about 12,000 to more than 1 million Dalton. They accelerate chemical reactions tremendously and functions in aqueous solutions under very mild conditions of temperature and pH. Enzymes bind specific reactant molecules called substrates. Substrates bind to a particular site on the enzyme surface called the active site, where catalysis takes place.  Enzymes are highly specific: They bind specific substrates and catalyze particular reactions under certain conditions. The specificity of an enzyme results from the exact three-dimensional shape and structure of the active site  ACTIVE SITES Enzyme molecules contain a special pocket or cleft called the active sites.  APOENZYME and HOLOENZYME The enzyme without its non protein moiety is termed as apoenzyme and it is inactive. Holoenzyme is an active enzyme with its non protein component.  Cofactor A cofactor is a non-protein chemical compound that is bound (either tightly or loosely) to an enzyme and is required for catalysis. Types of Cofactors: ‒Coenzymes ‒Prosthetic groups  Types of Cofactors Coenzyme: The non-protein component, loosely bound to apoenzyme by non-covalent bond. Examples : vitamins or compound derived from vitamins. Prosthetic group The non-protein component, tightly bound to the apoenzyme by covalent bonds is called a Prosthetic group.  Enzyme Specificity Enzymes have varying degrees of specificity for substrates Enzymes may recognize and catalyze: - a single substrate - a group of similar substrates - a particular type of bond  Activation energy or Energy of Activation All chemical reactions require some amount of energy to get them started. OR It is First push to start reaction. This energy is called activation energy. Mechanism of Action of Enzymes Enzymes increase reaction rates by decreasing the Activation energy: Enzyme-Substrate Interactions: ‒ Formation of Enzyme substrate complex by ‒ Lock-and-Key Model ‒ Induced Fit Model Enzymes Lower a Reaction’s Activation Energy  Lock-and-Key Model In the lock-and-key model of enzyme action: - the active site has a rigid shape - only substrates with the matching shape can fit - the substrate is a key that fits the lock of the active site This is an older model, however, and does not work for all enzymes  Induced Fit Model In the induced-fit model of enzyme action: - the active site is flexible, not rigid - the shapes of the enzyme, active site, and substrate adjust to maximumize the fit, which improves catalysis - there is a greater range of substrate specificity This model is more consistent with a wider range of enzymes  Enzyme-substrate complex Step 1: Enzyme and substrate combine to form complex E + S ES Enzyme Substrate Complex +  Enzyme-product complex Step 2: An enzyme-product complex is formed. ES EP ES transition EP state  Product Step 3: The enzyme and product separate EP E + P The product is made Enzyme is ready EP for another substrate.  What Affects Enzyme Activity? Three factors: 1. Environmental Conditions 2. Cofactors and Coenzymes 3. Enzyme Inhibitors 24  1. Environmental Conditions 1. Extreme Temperature are the most dangerous ‒ high temps may denature (unfold) the enzyme 2. pH (most like 6 - 8 pH near neutral) 3. Substrate concentration. 25  Environmental factors Optimum temperature The temp at which enzymatic reaction occur fastest.  Environmental factors pH also affects the rate of enzyme- substrate complexes – Most enzymes have an optimum pH of around 7 (neutral) However, some prefer acidic or basic conditions  Substrate Concentration and Reaction Rate The rate of reaction increases as substrate concentration increases (at constant enzyme concentration) Maximum activity occurs when the enzyme is saturated (when all enzymes are binding substrate)  2. Cofactors and Coenzymes Inorganic substances (zinc, iron) and vitamins (respectively) are sometimes need for proper enzymatic activity. Example: Iron must be present in the quaternary structure - hemoglobin in order for it to pick up oxygen. 29  3. Enzyme Inhibitors Competive - mimic substrate, may block active site, but may dislodge it.  Enzyme Inhibitors Noncompetitive