Enzymes PDF

ENZYMES  ENZYMES ▪Enzymes are biological catalysts (also known as biocatalysts) that speed up biochemical reactions without undergoing a change in living organisms. They are essential for respiration, digestion, muscle, and nerve function. ▪Catalyst- A substance that speeds up a chem...

ENZYMES  ENZYMES ▪Enzymes are biological catalysts (also known as biocatalysts) that speed up biochemical reactions without undergoing a change in living organisms. They are essential for respiration, digestion, muscle, and nerve function. ▪Catalyst- A substance that speeds up a chemical reaction without being changed or consumed in the reaction. An enzyme is a biological catalyst that increases the rate of a chemical reaction without being changed in the process.  PROPERTIES OF ENZYMES Most enzymes are proteins, which are large, complex molecules made up of long chains of amino acids. 2. Enzyme-catalyzed reactions usually take place under relatively mild conditions (temperatures well below 100oC, and neutral pH). 3. Enzymes are specific because different enzymes have differently shaped active sites. The shape of the active site of an enzyme is complementary to the shape of its specific substrate. This means they are the correct shapes to fit together. 1. Active site – the part of an enzyme that directly binds to a substrate and carries a reaction. 2. Substrate – the substance on which the enzyme acts. The substrate is the starting material for a chemical reaction. 3. An enzyme-substrate complex- is a temporary molecule formed when an enzyme comes into perfect contact with its substrate. 4. Product – A product is a compound obtained at the end of a chemical reaction. PARTS OF THE ENZYME ▪Apoenzyme ▪Holoenzyme ▪Cofactor ▪Coenzyme  PARTS OF THE ENZYME APOENZYME ▪Apoenzyme or apoprotein is an enzymatically inactive protein part of an enzyme, which requires a cofactor for its activity.  PARTS OF THE ENZYME COFACTORS ▪ Cofactors are "helper molecules" and can be inorganic or organic in nature. They assist enzymes during the catalysis of reactions.  THERE ARE THREE KINDS OF COFACTORS PRESENT IN ENZYMES 1. Prosthetic groups These are cofactors tightly bound to an enzyme at all times. By attaching to enzymes, prosthetic groups can make enzymes active/turn them on or increase their activity Example: Heme  THERE ARE THREE KINDS OF COFACTORS PRESENT IN ENZYMES: 2. Coenzyme - binds to enzyme only during catalysis. At all other times, it is detached from the enzyme. NAD+ is a common coenzyme. ***Nicotinamide adenine dinucleotide. 3. Metal ions are essential for the catalytic action of some enzymes. Metal ions contribute to the catalytic process through their ability to attract or donate electrons. ▪Metalloenzymes are enzyme proteins containing metal ions as metal cofactors.  PARTS OF THE ENZYME HOLOENZYME ▪ Holoenzyme is a complete, functional enzyme, which is catalytically active. Holoenzyme consists of an apoenzyme together with its cofactors. Holoenzyme contains all the subunits required for the functioning of an enzyme. HOLOENZYME = APOENZYME + COFACTOR TWO MODELS THAT EXPLAIN ENZYME SPECIFICITY  LOCK AND KEY MODEL ▪ In the lock-and-key model, the substrate and the enzyme possess specific complementary geometric shapes that fit exactly into one another. Like a key into a lock, only the correct size and shape of the substrate (the key) would fit into the active site (the keyhole) of the enzyme (the lock).  INDUCED FIT MODEL ▪ It suggests that the active site continues to change until the substrate is completely bound to the active site of the enzyme, at which point the final shape and charge are determined. Unlike the lock-and-key model, the induced fit model shows that enzymes are rather flexible structures. COMPONENTS OF ENZYME  OXIDOREDUCTASE ▪Oxidoreductases are a broad group of enzymes that catalyze electron transfer from one molecule to another (a reductive molecule or an electron donor) (the oxidant or the electron acceptor). ****Oxidant = is defined as an electron acceptor. ***Reductant= is defined as an electron donor.  TRANSFERASES ▪Transferases are enzymes that catalyze the transfer of a functional group from one molecule to another. Example of functional groups: Hydroxyl, sulfhydryl, carbonyl, carboxyl, amino, and phosphate groups  HYDROLASES ▪Hydrolases are the group of enzymes that catalyze bond cleavages by reaction with water. The natural function of most hydrolases is digestive to break down nutrients into smaller units for digestion. ▪ Digestive enzymes are classified as hydrolases because they break down large and complex food into small and simple ones with the use of water. For example: 1. Amylase - made in the mouth and pancreas; breaks down complex carbohydrates. 2. Lipase - made in the pancreas and stomach; breaks down fats. 3. Protease - made in the pancreas, stomach, and small intestines; breaks down proteins.  ISOMERASES ▪ Isomerase enzymes catalyze the structural shifts present in a molecule, thus causing the change in the shape of the molecule. ▪ Isomerases are a general class of enzymes that convert a molecule from one isomer to another. Isomer - two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties. LYASES ▪ Adds water, carbon dioxide, or ammonia or eliminates them to create double bonds. ▪ For example, the enzyme histidine ammonia- lyase catalyzes the reaction shown to the left which results in the formation of a double bond. Lyases are the enzymes responsible for catalyzing addition and elimination reactions.  LIGASES ▪ Ligase is an enzyme that can catalyze the ligation (joining ) of two large molecules by forming a new chemical bond. DNA ligase is a DNA-joining enzyme. If two pieces of DNA have matching ends, ligase can link them to form a single, unbroken molecule of DNA.  FACTORS AFFECTING ENZYME ACTIVITY  TEMPERATURE ▪Enzymes are picky molecules. They work within a very specific range of conditions and fall apart when those conditions are violated. ▪Every enzyme has an optimum temperature—the temperature at which it works best. ▪The rate of reaction is greatest at the optimum temperature.  ENZYME DENATURATION ▪Enzyme denaturation occurs when an enzyme loses its native conformation, or three-dimensional structure, rendering it unable to bind to substrate and catalyze product formation. If the temperature is too high the enzymes denature, the active site changes shape and the enzyme-substrate complex cannot form.  pH ▪Like temperature enzymes also have different optimum pH values at which the enzyme functions effectively. ▪A pH value which is very different from the optimum pH can result in denaturation.  ENZYME AND SUBSTRATE CONCENTRATION ▪Increasing enzyme concentration will speed up the reaction, as long as there is substrate available to bind to. Once all of the substrates are bound, the reaction will no longer speed up since there are not enough enzymes available to attach to the substrate. ▪ Increasing substrate concentration also increases the rate of reaction to a certain point. Once all of the enzymes have bound, any substrate increase will have no effect on the rate of reaction.  ENZYME INHIBITORS 1.COMPETITIVE INHIBITORS -are the same shape as the substrate and can bind to the active site. This prevents the substrate from binding and the reaction from occurring. Competitive inhibition is reversible. It can be reversed by increasing the concentration of the substrate. 2. NON-COMPETITIVE INHIBITORS - Bind at a site other than the active site, the allosteric site. As a result, it causes the active site to change shape, and therefore the substrate can no longer bind regardless of how much substrate is added. THANK YOU ☺