2.5 - Enzymes

2.5 - Enzymes

Active sites and enzymes Enzymes: globular proteins that work as catalysts speed up biochemical reactions aren't altered themselves in reactions found in all living cells also secreted by some cells to work outside the substances that enzymes turn into products are substrates enzyme-substrate specificity: enzymes need to fit with the substrate active site: a region on the surface on the enzyme where substrates bind the shape and chemical properties of the enzyme and substrate match  this allows the substrate to bind, but not other substances substrates are converted into products when bound to the active site the products are then released, freeing the active site to catalyze another reaction

Enzyme activity is the catalysis of a reaction by an enzyme. three stages: the substrate binds to the active site of the enzyme, sometimes 2 substrates substrates change into different chemical substances, which are  the products products separate from the active site, leaving it free for substrates to bind a substrate molecule can only bind to the active site if it moves very close to it the coming together of a substrate and an active site is called collision   with most reactions, substrates are dissolved in water around the enzyme particles dissolved in water are in contact with each other and in continuous motion both substrates and enzymes with an active site are able to move but most substrates are smaller than the enzyme so they move faster collisions between substrate molecules and the active site occur because of random movements of both substrate and enzyme   successful collisions are ones where the substrate and active site are successfully aligned to allow binding to take place

Factors affecting enzyme activity temperature, pH and substrate concentration affect the rate of activity in enzymes   Temperature: 1st way in liquids, the particles are in continual motion higher temperatures increase the kinetic energy so both enzyme and substrate move faster therefore, enzyme activity increases 2nd way when heated, enzyme bonds vibrate more higher chance of the breaking of the bonds when the bonds break, the structure is changed this permanent change is called denaturation the active site also changes, so no binding as more enzymes are denatured, enzyme activity falls

pH the lower the pH, the higher the hydrogen ion concentration most enzymes have an optimum pH where their activity is highest if the pH is increased or decreased, enzyme activity decreases then falls because the structure of the enzyme is altered, including the active site beyond a certain pH, the structure of the enzyme is irreversibly altered, (denaturation) enzymes don't all have the same pH optimum this reflects the wide range of pH environments in which enzymes work for example, the protease secreted by Bacillus licheniformis has a pH optimum between 9 to 10. This bacterium is cultured to produce its alkaline-tolerant protease for use in biological laundry detergents, which are alkaline

Substrate concentration 1st way more substrates, more frequent collisions enzyme activity increases 2nd way after binding, the active site is occupied and unavailable more substrates, more occupied active sites a greater proportion of substrate-active site collisions are blocked the increases in the rate of reactions get smaller 

Denaturation like other proteins, enzymes' structure can be irreversibly altered by certain conditions can be caused by both high temperatures and either high or low pH when an enzyme is denatured, the active site is altered and a substrate cannot bind f it binds, the reaction that the enzyme normally catalyzes doesn't occur in many cases, denaturation causes enzymes that were dissolved in water to become insoluble and form a precipitate

Immobilized enzymes in 1897, the Buchner brothers showed that an extract of yeast, containing no yeast cells, would convert sucrose into alcohol Louis Pasteur had claimed that fermentation of sugars to alcohol could only occur if living cells were present part of the vitalism theory (stated that substances in animals and plants can only be made under the influence of a "vital spirit" or "vital force") the artificial synthesis of urea disproved this theory the Buchners' research provided a clearer falsification of the theory more than 500 enzymes now have commercial uses   the enzymes used in industry are usually immobilized this is the attachment of the enzymes to another material or into aggregations so that the movement of the enzyme is restricted there are many ways of doing this, such as attaching the enzymes into a glass surface trapping them in an alginate gel bonding them together to form enzyme aggregates enzyme immobilization has several advantages: the enzyme can be easily separated from the products of the reaction, stopping the reaction at the ideal time and preventing contamination of the products after being retrieved from the enzyme mixture, the enzyme can be recycled, giving useful cost savings, especially as many enzymes are very expensive immobilization increases the stability of enzymes to changes in temperature and pH, reducing the rate at which they are degraded and have to be replaced substrates can be exposed to higher enzyme concentration than with dissolved enzymes, speeding up reaction rates