Effect of Anaerobic Respiration On Yeast

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The Effect of Temperature on the Anaerobic Respiration of Yeast


To investigate the effect of temperature on the rate of respiration in a suspension of yeast Saccharomyces cerevisiae.

Background Knowledge:

Yeasts are a form of   classified in the  , with approximately 1,500  known. They reproduce  by  mainly, although some species reproduce by .

They are unicellular, although some species with yeast forms may become multicellular due to way in which they normally reproduce. Typically the size of a yeast cell is approximately 3–4  in  but this can vary greatly depending on the species.

The yeast species  has been used in  and   for thousands of years. It is also extremely important as a  in modern  research, and is the most thoroughly researched eukaryotic microorganism. Researchers can use it to gather information into the biology of the eukaryotic cell and human biology.

These microbes are thought to be one of the first domesticated organisms. People have used yeast for fermentation and baking throughout history. Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeasted bread, as well as drawings of 4,000-year-old bakeries and breweries.

It has many uses in the production of certain products , these include; Alcoholic beverages, Beer, Root beers, Soda, Distilled drinks, Wine, Baking, Bioremediation (process that uses , ,  or their enzymes to return the environment to its original state), Nutritional supplements, Science and Probiotics (dietary supplements).

Yeasts are  as they use  as a source of energy and do not require light to grow. The main source of carbon is obtained by  sugars such as  and , or disaccharides such as  and .

They will grow from 10°-37°C, with optimum temperature in the range of 30°-37°C, depending on the species.  There is little activity in the range of 0°C-10°C. Above 37°C yeast cells become stressed and will not divide properly.

Anaerobic respiration occurs when no free oxygen is present to remove the hydrogen. This therefore means the electron transport chain cannot continue to function and no more ATP can be produced via oxidative phosphorylation. Hence why a form of respiration is required without the need for oxygen.

Anaerobic respiration or fermentation as it is called when referring to some plant species (including yeast). This process does not require oxygen. Instead of oxygen reaction with the hydrogen to continue the processes such as the electron transport chain and oxidative phosphorylation, another substance is used. The hydrogen produced from the reduction of NAD is converted to ethanal. This frees up another NAD which allows glycolysis to continue.

Pyruvate is firstly decarboxylated to ethanal, which in turn is then reduced to ethanol.  This process is done by an enzyme called alcohol dehydrogenase. This process from glucose to ethanol is referred to as alcoholic fermentation.

The difference between anaerobic respiration and fermentation is the ability to recover from the effects. In anaerobic respiration the lactate build up can be removed in oxygen debt. 20% is oxidized in the liver, and the remaining 80% is converted to glycogen. However the effects of fermentation are permanent.

        Enzymes are fundamental to all metabolic pathways in respiration and anaerobic respiration, especially key in the ethanol pathway, whereby ethanal is converted to ethanol via an enzyme called alcohol dehydrogenase.

The lock and key mechanism describes enzyme catalyzed reactions. Similar to the role of alcohol dehydrogenase in the fermentation of yeast.

        The lock and key theory has substrate molecules and enzymes. All enzymes are a specific shape. There fore the substrate molecule must also have a specific shape for an enzyme to be able to react with it. This is known as the active site. For this reason the lock and key mechanism is known as substrate specific. For a reaction to take place, a compatible substrate molecule and enzyme must come together. The enzyme locks into the substrates active site and the required reaction takes place.

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There are many factors in which enzymes can be effected by environment however, such factors which can inhibit and in fact stop the enzyme catalyzed reactions from occurring. These factors therefore have an effect on the metabolic pathways involved in anaerobic respiration.

Temperature can have a positive and negative effect on enzymes. All enzymes have an optimum temperature at which they operate. This temperature is often the stage at which enzymes are most productive. Within the human body this usually between 30°C and 40°C.

 However if the temperature becomes too high or too low the ...

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***** A detailed account of an investigation with a very good understanding of background theory.