Anaerobic Fermentation By Yeast.

Mohammed Umar 13LXG

Anaerobic Fermentation By Yeast

Background Information

The majority of the reactions that occur in living organisms are enzyme-controlled. Without them, the rate of the reactions would be so slow as to cause serious, if not fatal, damage. Reactions proceed because the products have less energy than the substrates. However, most substrates require an input of energy to get the reaction going, (the reaction is not spontaneous). The energy required to initiate the reaction is called the activation energy. When the substrate(s) react, they need to form a complex called the transition state before the reaction actually occurs. This transition state has a higher energy level than either the substrates or the product. We have enzymes that provide an alternative way with a different transition state and lower activation energy.

Without enzymes toxins would soon build up and the supply of respiratory substrate would decrease. Enzymes are proteins and thus have a specific shape. They are therefore specific in the reactions that they catalyse – one enzyme will react with molecules of one substrate. Within the folds of each enzyme is the active site or the place where the substrate fits and where the chemical reaction takes place. Since the active site for all molecules of one enzyme will be made up of the same arrangement of amino acids, it has a highly specific shape.

Generally, there is only one active site on each enzyme molecule and only one type of substrate molecule will fit into it. There are two main theories on how the substrate binds with the enzymes active site, the lock and key theory and the induced fit theory.

The lock and key theory is basically the enzyme is the same shape as the substrate so they fit with each other like a key would in a lock, however, it has been discovered that competitors for an active site (similar in shape to the substrate) could fit even though they are larger than the substrate. This means that the substrate and active site are a little flexible. This has lead to the induced fit theory. This is when the enzyme and substrate form a complex, structural changes occur so that the active site fits precisely around the substrate (the substrate induces the active site to change shape).

The reaction will take place and the product, being a different shape to the substrate, moves away from the active site. The active site then returns to its original shape.

Picture from Encyclopaedia Britania

For the experiment below the most important factor that will affect the rate of reaction will be the temperature since all other factors will be kept constant. As the temperature increases, the rate of reaction will also get faster. Eventually, increasing the temperature will cause the enzymes to start denaturing when this happens the reaction will slow down and stop and the enzymes will become useless, the reason for this is the shape of the active site will change so no substrate can bind to it. Other factors that affect the enzymes performance will be kept constant these are mainly Enzyme Concentration and PH. For this experiment I will be using the enzyme present in Yeast.

Yeast are unicellular fungi. It has been around for along time and has been involved in the making of bread, wine and other materials for man. Now yeast is used in many different industries for its fermentation properties. During this process in the industries the yeast is the waste product and is usually used for animal food or birdseeds. However the alcohol is the valuable product in the industry. Yeast has been a major material to man for a long time and is now a very expensive and profitable material for businesses and industries.

The yeast respires to produce energy. When it does respire it produces and needs products and waste products, these are shown in the word equation below. To control this reaction the yeast has an enzyme; this enzyme is called Zymase.

Zymase is an enzyme that acts on a certain carbohydrate to produce carbon dioxide and water, or alcohol and carbon dioxide .

From

Enzymes are used to control the speed and the rate of the respiration in the yeast, it changes the rate and speed by the environmental surroundings it is put in. Fermentation of glucose by yeast produces ethyl alcohol and carbon dioxide.

Glucose, or monosaccharide sugar as it is sometimes known, has the chemical composition C6H12O6. You find it in honey and the juices of many fruits; the alternative name grape sugar comes from the presence of glucose in grapes. Glucose is a normal constituent of the blood of animals.

Glucose is a white crystalline solid but is less sweet than ordinary table sugar.

Glucose is formed from many carbohydrates, including sucrose, maltose, cellulose, starch, and glycogen. Glucose is made industrially by the hydrolysis of starch under the influence of dilute acid or, more commonly, under that of enzymes. It is chiefly used as a sweetening agent in the food-processing industries. It is also used in tanning, in dye baths, and in medicine for treating dehydration and for intravenous feeding.

Respiration usually happens in the presence of air (oxygen), this is called aerobic respiration. However respiration can also happen ...