Proteins
(Campbell 6th Ed. 71-80; 7th Ed. 77-86)

• Enzymes
• Exercise 5 Effect of Temperature on Enzyme Activity

Proteins have numerous important roles in the living organism. Proteins form many structural features such as hair, hooves, and tendons. The elements in proteins are carbon, hydrogen, oxygen, nitrogen, and, in some proteins, sulfur.

All proteins are polymers of amino acids covalently bonded in long chains that subsequently coil and fold into complex shapes that determine the function of the resulting protein molecule. The chemical bond that holds amino acids together is called a peptide bond. The bond forms between the functional groups of two amino acids. Specifically, a peptide bond occurs between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of its neighboring amino acid. Many amino acids linked together form a polypeptide. Proteins are polypeptides.

What is the common feature between glycosidic and peptide bond formation?

Enzymes
(Campbell 6th Ed. 96-103; 7th Ed. 150-157)

Enzymes are a particularly important class of proteins. They control the many chemical reactions that keep the cell alive. Enzymes do this by acting as catalysts in biochemical reactions. Acting as catalysts the enzyme cause chemical reactions that would not occure in the absence of the enzymes or speed up reactions that would be very slow.

Exercise 5 - Effect of Temperature on Enzyme Activity

The enzyme you will be using, catechol oxidase, is found in plant tissues. We will obtain ours from the potato. Catechol oxidase is released when a plant cell is damaged, and reacts with catechol to form benzoquinone. Benzoquinone is toxic to bacteria and helps prevent decay in damaged plant tissue. Benzoquinone has a characteristic brown colour.

We will examine the rate at which catechol oxidase produces benzoquinone at different temperatures.

We used 5 test tubes set up as follows:

Tube 1	Tube 2	Tube 3	Tube 4	Tube 5
10 ml Water	10 ml Water	10 ml Water	10 ml Water	10 ml Water
-----	Cut-up Potato	Cut-up Potato	Cut-up Potato	Cut-up Potato
5 ml Catechol	5 ml Catechol	5 ml Catechol	5 ml Catechol	5 ml Catechol
Room Temp	100°C	Room Temp.	0°C	40°C

After 20 miniutes the tubes appeared as below:

Consider the following questions. For answers to the questions consult your lab manual, textbook and lecture notes. If you are still unsure consult with one of the instructors.

• What affect did tempurature have on the reaction?

• How would you explain the difference between the reaction at 100°C and at 40°C?

• When, in the fall, you harvest vegetables for prolonged storage in a freezer the maintain the best taste if they are first blanched (put in boiling water for a brief time).

• Can you provide an explanation for this?