Biology Lab 111L
October 25 2010
The experiment was conducted to determine the impact different sugar types have on yeast fermentation. It was hypothesized that glucose, sucrose and fructose would all produce energy through yeast fermentation, but that sucrose would have the greatest rate of energy production. The carbon dioxide production was tracked in the fermentation of yeast with solution of no sugar, glucose, fructose, and sucrose over a period of twenty minutes. All of the sugars produced energy, but glucose was the most efficient of the three, even producing energy at three times the rate of fructose. This difference in efficiency is a result of the various pathways the sugars must take to enter glycolysis. Glucose could enter directly while sucrose had to be broken down and fructose required modification to enter as an intermediate.
Respiration makes up a cell’s metabolic process where carbohydrates are converted into energy to be used by the cell. Cellular respiration can take one of two pathways; aerobic or anaerobic respiration. Anaerobic respiration occurs in the absence of oxygen. This pathway produces much less oxygen than aerobic respiration because only glycolysis occurs. The Krebs cycle and the electron transport chain are blocked since oxygen is not present to accept the electrons at the end. In anaerobic respiration, glycolysis is followed by a side reaction to regenerate the NAD+ used to accept electrons from the carbohydrate. In animals, this reaction is lactic acid fermentation while in plants and fungi, ethanol fermentation occurs. These methods are far less efficient than aerobic respiration (Cellular, 54). Ethanol fermentation begins after glucose has been converted into two pyruvates during glycolysis. This pyruvate then is broken into acetylealdehyde and a carbon is released in the form of carbon dioxide. Ethanol is formed through the reduction of acetylealdehyde by NADH (Freeman, 2011). Saccharomyces cerevisiae or baker ’s yeast is a type of fungus that undergoes ethanol fermentation when there is a lack of oxygen. In the wild, it is found on the skins of fruit and uses their sugars for food. Through its anaerobic respiration, it is used to produce ethanol for alcoholic drinks and allows bread to rise with its carbon dioxide production (Cummings, 2008). Since carbon dioxide is an immediate by-product of the anaerobic respiration of yeast, its production can be tracked to determine the efficiency of the energy production. There are many environmental factors that can impact the efficiency of the energy yield of baker’s yeast. These include pH, temperature and available nutrients. The amount of carbon present is the most important nutritional requirement since yeast produces energy through the processing of carbohydrates (Cellular, 54).
Yeast is not limited to glucose for its sugar requirement in glycolysis. Different types of yeasts can process different forms of carbon compounds but most yeast can metabolize glucose and sucrose. Stelling-Dekker’s detailed studies on yeast also concluded that if a certain species of yeast can process glucose, it can also metabolize fructose and mannose. The majority of yeasts ferment glucose most efficiently, though there are some exceptions (Berg, 2002). Both glucose and fructose have the same molecular formula, C6H12O6, and form a hexacarbon ring. The only difference lies in the hydrogen-oxygen arrangements (Freeman, 72-73). Though glucose is the reactant in glycolysis, fructose is an intermediate before the formation of pyruvate and the raw form can enter the chain at the appropriate step (Berg, 2002). Sucrose is a polysaccharide that consists of glucose and fructose. Many types of yeast contain the necessary enzymes to break sucrose into the monomer subunits necessary for glycolysis...