Investigation on Effects of DOPA pH on Enzyme Activity

Topics: PH, Enzyme, Acid Pages: 6 (1225 words) Published: December 3, 2013
Investigation on Effects of Different pH on Enzyme Activity
How does the different pH buffers affect activity of potato enzyme/extract?

Proteins are polymers that are made up of smaller units/monomers called amino acids. There are 20 different types of amino acids, thus make up many different combinations in types, numbers of amino acids as well as their orders – an explanantion for why there are so many proteins. Every protein, due to various reactions of amino acids to each other, have its own three dimensional structures and therefore, function (Reece JB and others 2011). Proteins are fundamental substance that perform various range of metabolism in the organism’s body such as fighting pathogens, sending signals, catalyzes reactions, storing substance, or acting as building blocks of body parts (Reece JB and other 2011). Proteins are grouped into four structures includin primary, secondary, tertiary, and quarternary. Primary structure of protein is composed of a single chain of amino acid without any foldings (The Medical Biochemistry Page, 2013). However, most proteins are active under secondary, tertiary, or quarternary structures. These strucures involve foldings due to the attachment between amino acids including hydrogen bonds, disulfide bridges, and Van de Waals force (The Medical Biochemistry Page, 2013).

Proteins could be denatured due to the effects of temperature or pH. A decrease in pH level causes the environment surrounding to have a more positive charge while an increase in pH level causes the surroundings to have a more negative charge. (Aune, Salahuddin, Zalengo and Tanford 1967).

Enzyme is a type of proteins that, by decreasing the activation energy needed for a chemical reaction, can therefore gives a start to that chemical reaction. Either catabolic or anabolic reactions need an enzyme to occur (Reece JB and others 2011). Every enzyme has an active site (Reece JB and others 2011). Enzymes metabolism occurs as enzyme binds to a substrate, which is specific to its enzyme’s structure and function, to form an enzyme2

subtrate complex (The Medical Biochemistry Page, 2013). As an enzyme binds to its substrate, the enzyme slight changes shape. (Reece JB and others 2011) Enzymes are denatured due to changes in temperature and pH as other types of proteins are. A slight change in pH away from the protein’s optimal pH level can cause huge loss to the activitiy of an enzyme. In a strong basic or acidic pH solution, enzymes are denatured quickly and lose their functions. For most proteins, the optimal pH is around 7.2 and 7.4 (University Leipzeig, 2013).

In this experiment, the enzyme activity (which is included in the potato extract) is measured in DOPA of pH 6.8 and of pH 5.0. If enzyme activity is measured in environment of DOPA pH 6.8 and DOPA pH 5.0, enzyme activity will be higher in DOPA of pH 6.8 and lower in DOPA pH 5.0. By changing the pH of DOPA to 5.0, pH of the environment that the enzymes are introduced in are shifted away from its optimal pH, causing denaturation and lowering enzyme activity, resulting in lower enzyme activity comaring to DOPA pH 6.8. Materials and Methods:

Gloves and goggles were always on over the course of this lab. Potato extract and four 15mL conical tubes were obtained. One was labeled “phosphate buffer” and 5mL of 0.1M phosphate buffer was added in. Another one was labeled “dH2O” and add 5mL of distilled water. Another conical tube was labeled “DOPA 5.0” and add 3mL of DOPA pH 5.0. The last one was labeled “DOPA 6.8” and add 3mL of pH 6.8. Everything was kept on ice until needed. Spectrometer was calibrated followed inspector’s instruction. Then 4 cuvettes were obtained. For the first cuvette, 2mL of DOPA 6.8 and 100µL of enzyme were added (enzymes should always be put last into the cuvettes). This cuvette was then placed in the spectrometer and spectrometer was used to measure enzyme activity. When absorbance data reached 200s in spectrometer, this...

Cited: October 22, 2013]. Avaiable from
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