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留学生生物学作业assignment代写案例

发表时间:2014-12-23 13:14:14

生物学assignment代写案例

此研究的目的是找出是否改变底物浓度都会对酶活性的活性的任何影响。酶在生物学上很常见,也是我们日常生活中必不可少,也几乎参与了所有新陈代谢反应,本文以研究报告report的形式,通过实验研究了酶的一些生物特性。

title:The Effect of Substrate Concentration on the Activity of the Enzyme Catalase

The aim of this investigation is to find out if changing the substrate concentration will have any effect on the activity of the enzyme activity. 

Enzymes are a very important for all living things. This is because they are essential to life as they are used in virtually every metabolic reaction. They are designed to work within a temperature range of 5-40??C, they do this as if it was any higher it would damage living cells. 

We call an enzyme a Biological Catalyst. A catalyst is a molecule which speeds up a reaction. They are very important as if they were not there reactions in cells would be to slow to support life. 

They speed up reactions by lowering the activation energy needed in the reaction. The activation energy is the energy needed to get a reaction going e.g. activation energy is like pushing a rock to the top of a hill and then pushing it off the top. The activation energy is the energy needed to get the rock to the top of the hill. When it is pushed of the top it no longer needs any help and it does it by itself. 

The diagram below explains activation energy: - 

Activation energy graph without enzyme 

This graph show the energy with is needed to get a reaction going i.e. activation energy. 

Activation energy graph with enzyme 

This graph shows what happens to activation energy when an enzyme is added to the reaction. You can clearly see the difference and this shows why enzymes speed up (catalyse) reactions. 

There are two types of enzyme reaction, these are: - 

* Anabolic - involved in synthesis 

* Catabolic - involved in breakdown (yeast and hydrogen peroxide is this type of reaction) 

One amazing thing about an enzyme is that when it is used in a reaction it will come out after the reaction exactly the same it was when it went in. 

All enzymes are globular proteins but not all globular proteins are enzymes. They have a three dimensional structure with hydrophilic R-groups arranged on the outside to ensure that the molecule is soluble. 

Enzymes are specific, this means that each enzyme will only work with one reaction or one small group of reactions. This because each enzyme has an active site this is a cleft in the enzyme surface where substrate molecules can bind.The substrate molecule has to be the correct shape for the enzymes active site or otherwise it will not fit. This is the lock and key hypothesis. If the substrate does not fit to the active site it tells you that it is not the specific enzyme for the active site. 更多资讯,请访问;http://www.lxws.net/new.php

Fisher's lock and key hypothesis above (diagram from Biological Science) 

It is not enough for the substrate just to fit into an active site it need an attractive force to keep it in place. The attractive forces are 

* Electrostatic attraction between oppositely charged groups 

* Hydrogen bonding 

* Permanent dipole-permanent dipole forces 


* Instantaneous dipole-induced dipole forces 

Once an enzyme molecule and a substrate molecule have joined together it is called an enzyme/substrate complex. 

In this investigation enzyme catalase accelerates the breakdown of hydrogen peroxide into water and oxygen. This catalase-mediated reaction is extremely important in the cells because it prevents the hydrogen peroxide building up in the cells. Hydrogen peroxide is a strong oxidizing agent which tends to disrupt the delicate balance of cell chemistry. 

The Plan 

Variables 

When you investigation enzyme activity there are several variables you can change or modify, these are: - 

* Temperature 

* Ph level 

* Substrate concentration 

* Enzyme concentration 

* Inhibitors 

Temperature - this is where you would keep the same amount of substrate and enzyme but change the temperature. You would have a large range of temperatures (probably 10??C to 60??C). This is so you can see when the enzyme is denaturized at 40?? and then see the enzyme activity drop. 

Ph level - this is where you would test the same amount of substrate and enzyme but change the ph level. You would probably use a wide range of ph levels to see how it behaves in an acid, neutral and an alkaline solution. 

Substrate concentration - this is where you would use change the concentration of the substrate and keep the enzyme concentration the same. Again you would want to use a wide range of concentrations so you would get a wide range of result. Then from these you could draw conclusions. 

Enzyme concentration - this is basically the same as substrate concentration but you keep substrate the same and change enzyme concentration. As with substrate concentration you would want to use a wide range of concentrations. This is so you would get a wide range of results. In which you could draw conclusions. 

Inhibitors - this is where you use the same enzyme and substrate concentration but change the amount of inhibitors used. I.e. you could have 0% inhibitors to 100% inhibitors. This would show you what affect in inhibitors have on enzyme activity. 

Catalase Enzymes 

Catalase enzymes are enzymes which speed up reactions. Catalase enzymes are some of the most potent catalysts known. The reactions it catalyses are crucial to life. The catalase enzymes convert Hydrogen Peroxide, a powerful and potentially harmful oxidizing agent into water and oxygen. This is very important to life as if it did happen 

your body would allow Hydrogen Peroxide to build up in the cells. This would cause harm to your body. So the body has catalase enzymes which break up Hydrogen Peroxide in oxygen and water. One example of a Catalase enzyme is Yeast. Yeast is the catalase enzyme which is going to be used in this investigation. 

In this investigation it will look at how Substrate Concentration affects enzyme activity. 

What enzyme and substrate? 

For the investigation the enzyme and substrate that will be used is Hydrogen Peroxide and Yeast. Hydrogen is the substrate and yeast is the enzyme. The formula for the reaction is:- 

Catalase Yeast added (enzyme) 

Hydrogen Peroxide = Water + Oxygen 

2H 2 O 2 = H 2 O + O 2 

When hydrogen peroxide is left it will slowly decompose naturally into water and oxygen just from energy from the sun. This is why it is rarely kept in a clear bottle as it would otherwise decompose into water and oxygen. For this to happen it would take a very long time, this is why an enzyme was added. The enzyme acts as a catalyst and speeds up the reaction causing the water and oxygen to be released a lot quicker than it would take to naturally decompose. 


The enzyme can speed up the reaction rate of the hydrogen peroxide because yeast enzyme fits the hydro peroxide active site. When the yeast binds with the substrate it creates an enzyme-substrate complex. The enzymes interaction with substrate causes it to break down into two product molecules (water and oxygen) leaving the yeast enzyme unchanged. 

What must be kept the same? 

To ensure that the investigation is reliable there are several steps which have to be taken to ensure this. These are:- 

Keep enzyme concentration the same 

Stir the yeast 

Repeat test to increase reliability 

Use same enzyme concentration in each test 

Prediction 

The reaction will start very quickly with as enzyme and substrate are mixed. When the reaction starts bubbles of oxygen will be produced. The largest volume of oxygen will be recorded in the first minute than any other minute. This means the initial speed will be faster in the first minute than any other minute. When substrate concentration is 
increased the speed of the initial reaction will increase. This tells us that substrate concentration is proportional to the initial rate i.e. as substrate concentration increase the initial rate increases and when initial rate increase substrate concentration increases. In the later stages of the reaction the reaction will get slower and less gas will be produced until in stop completely. This will be cause the reaction not to be proportional any more. 

This means the results which should be expected from the experiment are 

* Very high volumes of oxygen when there is a high substrate concentration 

* Then very low volumes of oxygen when there is low substrate concentration 

This will mean the curve on the graph will be steep at the beginning where the reaction is at its fastest but as the reaction goes on it will level off 

The graph should look like this: - 

Scientific knowledge can be used to explain why the above prediction was correct. The initial reaction rate will be higher with a higher substrate concentration and lower with a lower substrate concentration. This is because at a higher substrate concentration there will be more hydrogen peroxide (substrate) molecules available to collide with the enzyme (yeast) active sites. This means at a lower substrate concentration the rate of reaction will be lower because there will be less substrate so it will take them longer to collide with the enzymes active sites and bind with them.
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