Determine the amount of gas evolved by the fermentation of different sugars by yeast.

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Title: Specificity of enzymes: sugars metabolized by yeast

Date: 6 October, 2004

Aim: To determine the amount of gas evolved by the fermentation of different sugars by yeast.

Theory:  

In the absence of oxygen cellular respiration stops with glycolysis.  The Krebs cycle and electron transport chain do not function.  Pyruvate accumulates in the cytoplasm and oxidized form of NADH (NAD+) is depleted.  When all of the  NAD+ is gone, glycolysis stops and the cell dies.  To avoid death, cells possess alternate pathways to regenerate NAD+ and keep glycolysis functioning in the absence of oxygen.  This process is called anaerobic respiration or fermentation. In anaerobes, glycolysis and fermentation are the only respiratory pathways present.  In plants and some fungi, fermentation converts pyruvate (3 carbons) to ethanol (2 carbons) and CO2.  Synthesis of the ethanol provides an electron (and hydrogen) acceptor that regenerates NAD+ from NADH and allows glycolysis to continue. Yeast belongs to the group of organisms called fungi.  The fungi cannot produce their own food, but given the right kind of food, yeast cells can perform the reactions of fermentation, producing carbon dioxide (a gas) and ethanol.  The rates of the chemical reactions of fermentation depend on the action of enzymes. The enzymes present in yeast cells are specific and will only catalyse the fermentation of certain sugars and not others.           

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Yeast fermentation gives the following during reaction:

C6H12O6-------> 2CH3CH2OH + 2CO2 + energy

         Enzymes

Glucose ---------------> carbon dioxide + ethanol + energy (ATP)

                                                (a gas)

Material:

  1. 5 – fermentation tubes, labeled 1 through five.
  2. 5 large test-tubs
  3. constant-temperature water bath (37oC)
  4. pipettes
  5. mm ruler
  6. 20% solution of each: dextrose, fructose, sucrose, maltose
  7. distilled water
  8. 10% baker’s yeast suspension

Procedure:

  1. Five fermentation tubes were labeled upside down near the bottom.
  2. To each test tube 2 ml of water is added and 2ml of each of the sugar solution in different test tubes, ...

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