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Basic Chemistry for Investigating Living Systems

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Basic Chemistry for Investigating Living Systems

  1. Answers

  2. Basic Chemistry for Investigating Living Systems

Exercise 1: Testing for the Presence of Proteins in Cells

Results: 

        Table 1:  Biuret Reagent Test for Protein in Cells

Test Tube

Contains

Hypothesis:

Contains Protein Yes or No?

Final Color

Is test substance present/absent?

1

Water

No

nearly colorless

absent

2

Albumen

Yes

amber-purple

present – lesser concentration

3

Amylase

Yes

lavender-purple

present – high concentration

4

Potato Starch

No

nearly colorless

absent

5

Onion Juice

No

amber-purple

present – lesser concentration

6

Potato Juice

No

amber -purple

present – lesser concentration

.

Any time you see a chemical with an ending, -ase, assume it is an enzyme. Enzymes are proteins.

Conclusions:

  1. What is the test substance? The test substance is protein.

  1. Which test tube represents the control? The tube that contained distilled water (tube 1) was the test tube that represents the control.  Why? When protein molecules are present, Biuret Reagent reacts with the protein to form a violet color. Tube number one is the control tube because it is distilled water and has no protein; the tube is colorless. If one knows that colorless represents no protein and violet color represents the presence of protein, one can use tube one to determine whether or not protein is present. (More information. You can look up Biuret Reagent to actually see how the chemical reaction occurs.)
  1. Which test tube contained the most test substance?  The tube that contained the most test substance is amylase (tube 3).
  1. Other than the control, which test tube contained the least test substance? None of the test tubes contained protein. If there would have been a reaction I would assume that there was some cross contamination.
  1. Did the results agree with your initial hypothesis in every case? My results did agree with my initial hypothesis in every case. Why or why not?  My hypothesis was correct when I expected Albumen to have protein. This was true because I’ve always heard that eggs are a good source of protein so I expected that albumen would test positive for protein. My hypothesis was correct when I expected Amylase to have protein. Amylase is an enzyme that breaks down starch into sugar. As stated in the lab, starches and sugars are carbohydrates and the interconversion of carbohydrates and fats are aided by enzymes which are proteins. My hypothesis was correct for potato starch. I didn’t expect potato starch, which I associate with a carbohydrate, to have protein. I was correct with my hypothesis of onion juice and potato juice not having any protein them.
  1. What are your conclusions about your results? Based on my results, I have concluded that protein is very abundant in certain foods. Meat, eggs, nuts, to mention a few. Of course all foods have protein, since cells have them. But this Biuret reagent is not able to detect very small amounts of protein. For that we would need to use special equipment. 
  1. If the color change is not as you expected, what might be the reasons? Probably due to contamination.
  1. Add another 5 drops of Biuret Reagent to each test tube and stir as before. Do your results change?  When I added five more drops of Biuret Reagent to each test tube I didn’t notice any changes from my initial results.

Discussion:

  1. What is the purpose of this exercise? The purpose of this exercise is to use colorimetry to qualitatively detect cellular chemical compounds, in this case detect protein. Proteins are polymers of amino acids that form peptide bonds. It is known that biuret reagent reacts with peptide bonds to form a violet color. One can know whether or not a substance contains protein by the color of the reaction with biuret reagent.

  1. Why is it important to clean droppers and equipment between chemical uses? It is important to clean droppers and equipment between chemical uses because one does not want to cross-contaminate the liquids and one needs to protect the parent source of liquids. 
  1. What other types of foods or substances contain high levels of protein?  Hair, Fingernails, Enzymes and Muscle tissue (meat) also contain high levels of protein.
  1. Suggest a situation where you might use the Biuret Reagent colorimetric test.  One could use the Biuret Reagent colorimetric test to test for protein in urine. Our body needs protein and some diseases and conditions can allow proteins to pass through the filters of the kidneys resulting in protein in urine. Some of these diseases and conditions are diabetes, chronic kidney failure, leukemia and Hodgkin’s disease.
  1. What other types of analytical procedures detect the presence of proteins?  In addition to the Biuret Reagent colorimetric test, one could detect the presence of proteins by using the Kjeldahl method, Enhanced Dumas method, Lowry Method, Dye binding method and the Turbimetric method.

Exercise 2:  Testing for the Presence of Starch in Cells

Results:

Table 2:  Iodine Solution Test for Starch in Cells

Test Tube

Contains

Hypothesis
Contains Starch Yes or No?

Final Color

Is test substance present/absent?

1

Water

No

amber

absent

2

Albumen

No

amber

absent

3

Amylase

No

amber

absent

4

Potato Starch

Yes

black/blue

present – high concentration of starch

5

Onion Juice

Yes

amber

absent

6

Potato Juice

Yes

black/blue

present – high concentration of starch

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