Reference no: EM133664916

Identifying macromolecules

In this week's practical we will focuson the topic of macromolecules. We will specifically be looking at identifying the presence of various macromolecules and determining their relative concentrations in samples. We will use the Benedict's test for reducing sugars to identify the presence of some carbohydrates. We will also use the Biurets reagent to identify the presence of proteins. Please read through the below practical instructions in conjunction with your week 2 and 3seminar/lecture notes on"chemicals of life","carbohydrates" and "proteins"in preparation for practical class.You can also prepare by considering how you can presentyour results.

Objectives
By the end of this practical session, you should be able to demonstrate an ability to:
• Perform tests to detect the presence of carbohydrates and proteins
• Determine the relative concentration of carbohydrates and proteins in samples
• Characterise an unknown compound
• Understand the importance of controls
• Accurately present data in a table

A. Identification of carbohydrates: Benedict's test for reducing sugars
Reducing sugars consist of a specific functional group that can reduce weak oxidising agents such as the copper (Cu2+) in Benedict's reagent. Oxidised Benedict's reagent is blue in colour (refer to image below). When reduced, copper oxide turns green to reddish orange in colour (as per image below). A green solution indicates a small amount of reducing sugar, while a reddish orange solution indicates an abundance of reducing sugar. In the presence of a non-reducing sugar there is no colour change. In the following exercise you will be using Benedict's reagent to detect the presence of a reducing sugar in a range of samples.

1. Collect 11 test tubes, place in a tube rack and label them 1 through to 11 using a permanent marker. These will correlate to samples 1 to 11 summarised in Table 1.1. Make sure you put your initials on each tube.

2. Prior to setting up your experimentpredict the reactivity for each tube in the table provided in the report section of the handout.
Table 1.1 Samples to be tested in the identification of carbohydrate activity.

3. To each tube add 10 drops of the solution to be tested.

4. To each tube, add 2 mL of Benedict's reagent using the dispenser provided.
Note: make sure you listen to demonstrator instructions about dispensing

5. Place the tubes in a test tube rack and into the water bath which has been set to 75oC*. Incubate your samples for 5 minutes. *CAUTION:Beware of heat. Ensure you don't injure yourself, see demonstrator, use heat resistant gloves & refer to pre-lab safety instructions

6. After 5 minutes, collect your tubes from the water bath. Make sure you wear heat resistant gloves when doing so. Dry the rack on the towel provided and return to your workbench.

7. Allow the tubes to cool to room temperature.

8. Record the final colour of each tube in a table in your laboratory report.

B. Identification of proteins: Biuret test for proteins
Proteinmonomers are linked together via a peptide bond which can be identified using the Biuret test. Peptide bonds within proteins form a complex with Cu2+ found in Biuret reagent. When a minimum of ~6 peptide bonds are present in the solution a violet colour is formed. The more intense the violet colour, the more concentrated the protein solution.

1. Collect 7 test tubes, place in tube rack and label them 1 through to 7 using a permanent marker. These will correlate to samples 1 to 7 summarised in Table 1.2. Initial the tubes.
2. Prior to setting up your experiment predict the reactivity for each tube in the table provided within the report section of this handout.
3. To each tube add 1 mL of the material to be tested summarised in Table 1.2.
4. To each tube, add 1 mL of 2.5% NaOH using dispenser provided.
5. Make sure you listen to demonstrator instructions about dispensing
6. To each tube, add 1mL of Biuret reagent.
7. Record the immediate colour change in a table in your laboratory report, making note of the intensity of the colour.

REPORT: PRACTICAL 1- IDENTIFYING MACROMOLECULES

Predictions

Prediction of Reducing Sugars: For each of the tube samples listed in part A of the practical,predict the resultant colour change upon addition of the Benedict's reagent and provide a brief sentence explanation as to why you expect the result you do. Clearly state which tubes are acting as either negative or positive controls[5 marks]
Note: Controls help to ensure the experiment is performed properly and to validate the result of an experiment. The positive control will be the sample that is known to produce the expected result. A negative control will be the sample which is not expected to produce any result.

Prediction of Proteins: For each tube sample listed in part B of the practical predict the resultant colour change upon addition of the Biuret reagent and provide a sentence explanation as to why you expect the result you do. Clearly state which tubes are acting as either negative or positive controls

Note: Controls help to ensure the experiment is performed properly and to validate the result of an experiment. The positive control will be the sample that is known to produce the expected result. A negative control will be the sample which is not expected to produce any result.

Results:

1. Draw a table recording your results for the identification of carbohydrates activity. Include in your table a column to indicate whether the result agreed with your predictions (a simple yes/no).Comment on the concentrations of glucose in Tubes 5, 6 and 7.

(Tip: Give your table an appropriate descriptive title. Refer to the Units, Tables and Graphing Guidelines reference document under the ‘Practicals Handouts & Submission Links' section of the course site on how to best present your data.)

2. Draw a table recording your results for the identification of proteins activity. Include in your table a column recording the colour intensity. This can be done in a few ways such as using a scale from 1 to 5, where 1 is no colour change and 5 is dark purple (make sure you define the scale). Also include a column to indicate whether the result agreed with your predictions (a simple Yes/No).
Remember to give your table an appropriate descriptive title.

Discussion:

1. Compare the results you achieved with your predictions for both Part A and Part B. Did you correctly predict the results?Discussany samples where your predictions did not match the results providing abrief explanation as to why you think this might be the case.[4 marks]
Make sure that your discussion is concise and well laid out so that the reader can interpret the discussion efficiently. If you do need to correct a prediction, make it very clear which Tube you are discussing e.g.

Part A: Tube 2 - Prediction incorrect because ..........
Tube 7 - Prediction correct but this can be better explained by .......

2. Name the monomer for the twotypes of macromolecules investigated in this practical.

3. Name the chemical reaction and the intramolecular bonding that linksmonomer subunits to form macromolecules. What is the special name given to this type of link in carbohydrates and in proteins?