how starch and cellulose are treated to allow them to be used by the yeast?
One potential ethanol feedstock is starch. Starch molecules are made up of long chains of glucose molecules. Thus, starchy materials can also be fermented after breaking starch molecules into simple glucose molecules. Examples of starchy materials commonly used around the world for ethanol production include cereal grains, potato, sweet potato, and cassava. A great amount of ethanol fuel is currently produced by starch fermentation. This starch comes from grains such as wheat and maize. Fermentation is produced by a yeast culture. The digestion of starch by yeasts is done in two stages: the starch is initially hydrolyzed in sugars by a chemical or enzymatic process then sugars are converted into alcohol and carbon dioxide by yeasts. This operation is effective and extracts the solar energy stored in the starch. * Enzymes are proteins which catalyse, or speed up, biological reactions. Enzymes usually have an -ase suffix, eg. lactase, protease, amylase and so on. Biological reactions are the reactions that occur in living things. For example, when we eat food we need to digest it. Without enzymes in our bodies, digestion could take weeks instead of a matter of hours. Enzymes are specific for a certain reaction, for example, the enzyme lactase will only work in reactions where the chemical lactose is present. Enzymes have a structure that is called active site. Only one substance can fit into the active site to be digested, and it is the only substrate that this particular enzyme works with.
The figure above shows the function of enzymes:
* The substrate enters the active site of the enzyme.
* The reaction takes place.
* The substrate exits the enzyme as two simpler products. You can also think of the way enzymes work as a key and a lock, the key is the substrate and the lock is the enzyme. The key should be exactly the right shape to fit in the lock, so does the substrate to fit in the active site of the enzyme. The key could only open only one lock, and the lock could be unlocked by only that key. Enzymes are two types, Builders and Breakers. Builder enzymes do the opposite of breaker enzymes. Breakers break large molecules into smaller simpler ones, builders combine smaller ones to make large molecules. Breaker enzymes are used in the digestive system to break down large insoluble molecules into simpler soluble ones to be used by the body. They are also present in cells that respire to break down sugars and oxygen into carbon dioxide, water and energy. Builder enzymes are present in plants to be used in photosynthesis, the opposite of respiration, in photosynthesis, oxygen and water are combined together to form carbon dioxide and sugars. Naming enzymes depends on the substrate they work on. For example: The sucrase enzyme works on sucrose.
The maltase enzyme works on maltose.
Enzymes are reusable and are only affected by the change in temperature and pH.
Several enzyme catalysed reactions occur during breadmaking. First, starch has to be broken down into sugar. The sugar then has to be broken down into simple sugars to allow yeast to react with these sugars during the process called fermentation (rising). Starch is made up of many glucose units joined together but yeast can't digest starch unless it is broken down into glucose units.
Affect of temperature on the enzyme’s activity:
Each enzyme has an optimum temperature, this is the temperature at which the enzyme is most active, below this temperature the activity of the enzyme decreases until it becomes inactive at low temperatures, above this optimum temperature the enzyme becomes denatured and can no longer work. At low temperatures the enzyme is and the substrate are moving very slowly and collide weakly, the enzyme is said to be inactive and doesn’t work. As the temperature increases, the enzyme and substrate gain more kinetic energy and move faster colliding...
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