The effect of the tempereature on yeast metabolism.

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  1. Introduction:

a. Title 

The effect of the tempereature on yeast metabolism.

b. Research Question 

What is the effect of a temperature on yeast metabolism? Five different water baths with different temperature of water inside (30oC, 40oC, 50oC, 60oC, 70oC) and a solution called TTC which is absorbed by the yeast cells turning them pink when hydrogen is removed from the metabolic pathway by the dehydrogenase enzyme will be used to see how the temperature affects the yeast metabolism. The effect of yeast metabolism will be measure by comparing 5 test tubes (as I measure five different temperature effects) with the cultures to the standards which are our samples. It is expected that the temperature will affect the metabolism of yeast.

c. Knowledge background 

There are many ideas to suggest that the change in temperature will cause an increase of respiration in yeast. Yeast is a single celled fungus made up mostly of protein, which is used in fermentation. Fermentation is the breakdown of sugars by bacteria and yeast using a method of respiration without oxygen (anaerobic respiration). It involves a culture of yeast and a solution of sugar (in my investigation it is a glucose), producing ethanol and carbon dioxide with the aid of the enzymes. The alcohol produced has been used in making wines and beers and the carbon dioxide produced has been used in baking as it gets trapped in the dough and causes it to rise.

Enzymes are catalysts that speed up reactions; they are made from protein and are specific as to which substrate they work on. For example a zymase-complex enzyme will only bind with a glucose molecule to produce the ferments carbon dioxide and alcohol.

Yeast has to make energy, stored as ATP to carry out all cellular functions. To do this they respire. They can respire both aerobically (when there is plenty of oxygen and the cells reproduce rapidly), or, where oxygen is short, they can respire anaerobically; in this process
they are called partial anaerobes. This is because less energy is released as the glucose sugar is only partially broken down, but still keeps the yeast alive. In my experiment the yeast is respiring by anaerobic respiration.

Here is the equation for anaerobic respiration:
Glucose
2 ethanol + 2CO2 + 2ATP

The Kinetic theory states that, with an increase in temperature, the rate of reactions will increase. This is due to the increase of speed of the particles, brought about by the extra energy given to them by heat. The faster particles will bring about more particle collisions and so the reaction will take place faster. Enzymes are sensitive to temperature changes up until a certain temperature and will increase in their activity up to this point. The reactions that take place in the enzymes will be quicker and so will create more of their products.

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But once you reach a certain temperature the rate of respiration slows down and drops. This happens because; all the enzymes are made up of protein chains of amino acids. They exist in the form of a helix structure with hydrogen bonds holding them together. When heat is applied to the enzyme, energy is given off. The active enzyme cell deforms and the hydrogen bonds break, denaturing the yeast enzyme. It would not be able to function as usual, and this process is irreversible.

c. Hypothesis 

If the temperature increased, then the metabolism of yeast will ...

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