Reaction Rates of Barley Alpha-Amylase Enzyme with Substrate Starch at Different Ph’s and Temperatures

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Abstract

Enzymes are proteins that lower the activation energy needed for chemical reactions. The two main environmental factors that can affect the enzyme’s activity are temperature and pH, and each enzyme works best at a particular temperature and pH. The purpose of this enzyme kinetic experiment was to observe the effect of temperature and pH on the reaction of barley alpha-amylase enzyme with starch substrate and establish the optimum temperature and pH for this reaction. The optimum temperature and pH for the reaction of alpha-amylase and starch was predicted to be a temperature of 50°C and a pH of 5. The optimum temperature and pH for the reaction was determined by monitoring the reaction rate of alpha-amylase at different temperatures and pH’s by means of using a spectrophotometer to measure the disappearance (in absorbance) of the substrate starch. As a result, the absorbance of the substrate starch decreased at different rates for each temperature and pH as time continued to increase. The results showed that the reaction rate with the enzyme is highest when it reaches a temperature of 50°C and has a pH of 5. Therefore, a farmer should grow barley seeds in soil that has a temperature of 50°C and a pH of 5.

Introduction

The purpose of this enzyme kinetic experiment was to observe the effect of temperature and pH on the reaction of barley alpha-amylase enzyme with starch substrate and establish the optimum temperature and pH for this reaction.

Enzymes are essential to all living organisms. An enzyme is a globular protein that acts as a catalyst, a chemical agent that speeds up reactions without being consumed by the reaction. They lower the activation energy needed for chemical reactions, allowing the reactant molecules to absorb enough energy to reach the transition state (Vliet 2008). When an enzyme binds to a substrate, it forms an enzyme-substrate complex. The substrate-enzyme complex allows the enzyme to react with the substrate in order to form the product (Vliet 2008). The enzyme is neither changed nor consumed during this process. Without the presence of enzymes, many of the chemical reactions in living cells would occur too slowly (Johnson and Raven 1998).

Specifically, the alpha-amylase enzyme is a type of enzyme found in barley plant seeds (Vliet 2008). Alpha-amylase catalyzes the breakdown of starch into glucose. Starch is a polysaccharide made up of glucose molecules (Johnson and Raven 1998). Starch is the substrate of alpha-amylase enzyme. Because glucose is a major cellular fuel, starch represents stored energy. According to Johnson and Raven (1998), the sugar can later be withdrawn from this carbohydrate “bank” by hydrolysis. Organisms have enzymes (such as alpha-amylase) that can hydrolyze plant starch (Vliet 2008). In addition, the organisms use the glucose molecules from starch as a nutrient for their cells.

The two main environmental factors that can affect the enzyme’s activity are temperature and pH. Each enzyme works best at a specific temperature and pH, known as the optimum. If the temperature or pH of the reaction is higher or lower than that of the optimum, the enzyme can break down (denaturation), which causes the active site to no longer fit the substrate molecule (Campbell and Reece 2008).

The enzyme, alpha-amylase, is harvested commercially from germinating barley seeds (Vliet 2008). Amylase hydrolyzes starch molecules to glucose, which is then taken up by the developing seedling. The reaction between alpha-amylase and starch was measured at specific temperatures and pH’s by using a spectrometer, an instrument that electronically measures the amount of a substance from its ability to absorb radiant energy (Vliet 2008). The alpha-amylase enzyme breaks down the starch within the solution and lowers the absorbance reading as time passes (Vliet 2008). The reaction rate of the alpha-amylase and starch reaction can be calculated using this data. In addition, the...
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