GENERAL BIOLOGY LAB 1 (BSC1010L)
Lab #3: Biologically Important Molecules
OBJECTIVES
• Learn the basic structure of the four types of biological molecules and the importance of each type.
• Understand the concepts of hydrolysis and dehydration synthesis
• Recognize the difference between a negative and positive control, and why these are used in experiments.
• Become familiar with the tests for different biological molecules.
READINGS and PROCEDURES TO PERFORM:
Exercise 6 (pgs. 55-62)
Procedures 6.1 – 6.5
INTRODUCTION:
Biological organisms are composed of four major classes of macromolecules; carbohydrates , proteins , lipids and nucleic acids . These macromolecules are important for proper cellular functioning and each plays a different role within the cell. For instance, carbohydrates are the primary energy source or “fuel” for cells, and are a major component of cell walls of bacteria, fungi and plants. Proteins function as “building blocks” or structural elements within the cell and play a role in the transport of molecules in and out of the cell. Lipids are not only used for “storage” of excess fuel but are also a key component of cell membranes.
Finally, nucleic acids (DNA and RNA) are considered the “information center” of the cell.
Nucleic acids comprise our genes, regulate cell function and are involved in energy transfer.
Both DNA and RNA are involved in cell replication, the process used to produce more cells.
Macromolecules vary in their elemental structure and thus their chemical properties
(Figure 1). This variation is advantageous since we can use it to aid in the identification of a particular macromolecule when examining an unknown substance. For example, carbohydrates are composed of monosaccharides. Monosaccharides contain either aldehyde (CHO) or ketone (-
C=O) side groups, which enables them to reduce oxidizing compounds. This oxidation produces a colored product which we can detect visually using the Benedict’s reagent (see procedures below).
In this lab we will use chemical tests to check for the presence of different macromolecules in known substances. We will also learn about the use of positive and negative controls and their function in determining the composition of an unknown substance. Controls are an essential component of any experiment. They are kept constant throughout the entire experiment and are compared against an experimental sample being tested. Two types of controls exist: negative and positive. A negative control provides an example of no effect after an experimental manipulation, while a positive control demonstrates what a positive result should look like (what to expect if the experimental manipulation produces a change). For example, if we want to test for the presence of salt in a substance, we could use a salt solution for our positive control. A good negative control for that test might be distilled water.
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Figure 1 : Basic structures and functional groups of macromolecules
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Task 1: Carbohydrates (pgs. 56-58)
1. Answer the following questions in the space provided. a.
How do mono-, di- and polysaccharides differ? b.
How are di- or polysaccharides formed from their monomeric building blocks? What is this process called and how does it work? c.
Explain, in your own words, what are negative and positive controls? Why do we use them? d.
How does the Benedict’s test work? What chemical reactions does it test for, and what does this have to do with carbohydrates? e.
Will a Benedict’s test be able to detect ALL sugars? Explain.
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2.
Perform Procedures 6.1 (pg. 57) and 6.2 (pg. 58) and answer the questions that follow in the space provided. Examples of the expected test results for positive and negative Benedict’s test (Fig 2) and Iodine test (Fig 3) reactions are shown below.
Figure 2: Examples of expected test results for positive and negative reactions in
Benedict’s test for reducing sugars.
Figure 3: Examples of expected test results for positive and negative reactions in the
Iodine test for starch.
•
Use the following table to record your predictions and observations for both the
Benedict’s and Iodine tests. Make sure to label the positive control (s) with an asterisk (*) and the negative control (s) with a double asterisk (**).
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7
4
5
3
2
Tube
#
1
Solution
10 drops onion juice
Benedicts Test
Predicted Result
(color)
Benedicts Test
Observed Result
(color)
Iodine Test
Predicted Result
(color)
Iodine Test
Observed Result
(color)
10 drops potato juice
10 drops sucrose
10 drops glucose
10 drops distilled water
6 10 drops reducing sugar
10 drops starch
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a.
What type of carbohydrate are we testing for when we use the Iodine test? Is this type of carbohydrate a mono-, di- or polysaccharide? b.
Based on both your answer to part a and your test results, what is the predominate carbohydrate in onion juice? What about potato juice?
Task 2: Proteins (pgs. 58-60)
1.
Answer the questions below: a.
What is the monomer of a polypeptide? What molecular structures indicate a molecule is a protein? b.
Using the Biuret test, what would a positive and a negative result indicate?
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c.
Hypothetically, you test two different substances for the presence of protein. One test provides a strong positive result and the other with a weak but still positive result. What does this indicate about the two samples?
1.
Perform Procedure 6.3 (pg. 60)
•
Use the table below to provide your predictions and observations for the Biuret test. Make sure to label the positive control (s) with an asterisk (*) and the negative control (s) with a double asterisk (**). Examples of the expected test results for positive and negative reactions are shown below (Fig 4).
A B C
Figure 4: Examples of expected test results for positive and negative reactions for the
Biuret test for protein.
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Tube
#
1
2
Solution
2ml egg albumen
1
Expected Result (color)
3
4
5
2ml honey
2ml amino acid solution
2ml distilled water
2ml protein solution
1
Albumen = clear liquid inside of an egg (“egg white”)
Task 3: Lipids (pgs. 60-62)
1. Answer the question that follows in the space provided: a.
Can a lipid dissolve in water? Why or why not?
Observed Result (color)
2.
Perform Procedure 6.4 (pg. 61)
• Prior to performing this test, provide your predictions for the outcome of each tube in the table provided:
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Tube #
1
2
Solution
5ml water
5ml acetone
1
Predicted Result Observed Result
1
Molecular formula for acetone:
( http://upload.wikimedia.org/wikipedia/commons/1/19/Acetone-structural.png
)
3.
Answer the following question: a.
How did this test for lipids incorporate what we know about a lipid’s structure and its solubility properties?
4.
Perform procedure 6.5 (pg. 62) and answer the questions that follow:
• Use the following table to provide your predictions and observations for the Sudan
IV test for lipid. Make sure to label the positive control (s) with an asterisk (*) and the negative control (s) with a double asterisk (**).Examples of the expected test results for positive and negative reactions are shown in Fig 5.
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A B http://faculty.cbu.ca/cglogowski/images/Lipid%20test.JPG
Figure 5: Examples of expected test results for positive and negative reactions for the
Sudan IV test for lipids.
Tube # Solution Predicted Result (color) Observed Result (color)
1
4
3
2
1ml salad oil + water
1ml salad oil +Sudan IV
1ml honey +Sudan IV
1ml distilled water + Sudan IV
5 1ml known lipid + Sudan IV
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a.
What was the purpose of tube 1? What was this controlling for? b.
Lipids contain twice as many calories when compared to carbohydrates. Given this fact and then looking at your test results, which has more calories, the salad oil or the honey?
Task 4: Nucleic Acids (pg. 62)
1. Answer the questions below: a.
How do DNA and RNA differ structurally? b.
What part of the structure of DNA allows for the formation of the double helix?
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c.
If you have a DNA sequence of ATTGCTAGCGCCAT, what would be the sequence of the complimentary strand?
Task 5: Identify Unknown Samples (Testing Substances from a Meteorite)
INTRODUCTION :
As a scientist, you will always work with unknowns. Using the scientific method, you can objectively and systematically identify these unknowns by formulating testable hypotheses that can be either accepted or rejected based on the results of carefully designed experiments. In the following task you will use the scientific method to formulate hypotheses and gather and interpret data. You will need to use the information you learned during current and previous labs to identify the molecule(s) that constitute(s) an unknown sample.
A meteorite has landed on the FIU campus and luckily it has fallen right in your lab. It has cracked open in the sterile environment of this lab, and a number of unknown substances are oozing out.
The Centers for Disease Control (CDC) and the Environmental Protection Agency (EPA) have asked that your team run tests on the unknown substances and report your findings. The CDC has quarantined this facility and no one will be allowed to enter or leave this room until the unknown substances are identified and are deemed safe.
A ll necessary equipment and supplies are provided to your team. To be certain about the content of the unknown substances, multiple trials need to be conducted and compared. Therefore each team will run the same trials. The CDC will not lift the quarantine until a consensus has been reached by all teams.
To begin your work on this task please fill out the CDC form provided.
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1. Unknown substances are coming out of the meteorite. Perform micro visual analysis of the oozing material. Report your findings in picture form below along with a written description of the material visualized..
DRAWINGS AND DESCRIPTIONS
Unknown Substance
__________________________________________________________________
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1. If your findings indicate possible cellular life forms in the unknown samples, can you help explain how these alien cells are similar to Earth-based animal and plants cells?
2. Provide a picture and written description of similar Earth-based living organisms (cheek cells and Elodea ) below.
3. Indicate how the alien sample compares to the cheek cells and Elodea cells. Perform
Procedures 4.8 (pg. 42) and 4.3 (pg 33) to prepare the cells.
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Cheek cells Elodea
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Confer with other teams to make sure you have all reached an agreement on the nature of these samples. What are these alien samples?
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Part II.
Based on your data, is living alien material comparable to cellular life forms present here on Earth? If yes, what kind of structures might be present in these alien cells and what would be their function?
Simple visual findings are not sufficient to convince the CDC, so more data will be required. You will need to determine if the “cells” osmoregulate and exchange matter with the environment like Earth-based living cells. The CDC will need to know if these alien samples are capable of the same processes. A simple way to visualize osmoregulation is by subjecting living cells to hyper- iso- and hypotonic solutions and observing the results.
In the table below, draw and explain what you expect to happen to Earth-based animal and plant cells in the three different environments:
HYPERTONIC ISOTONIC HYPOTONIC
Animal
Plant
Allow your TA to see these drawings above before proceeding.
Next: Demonstrate the response of known Earth-based animal and plant cells ( Elodea and cheek cells) to the three types of osmotic environments. Provide a written description of each process as well.
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HYPERTONIC
Elodea
ISOTONIC HYPOTONIC
Cheek cells
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
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______________________________________________________________________________
______________________________________________________________________________
Now demonstrate that the alien cells react similarly to the Earth-like animal and plant cells to the three types of osmotic environments. Provide a written description of each process as well.
HYPERTONIC
Unknown
ISOTONIC HYPOTONIC
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
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Finally:
1.
Collect about 2mL of meteorite ooze into each of 4 test tubes and label them as 1-4. Test tube 1 will be tested for the presence of reducing sugars (Benedict’s test), test tube 2 for the presence of starch (Iodine test), test tube 3 for the presence of protein (Biuret test) and tube 4 for the presence of lipids (Sudan IV).
2.
Use the table below to record the results of all your tests. Once every group has completed this task, you will discuss the results as a class.
TEST TUBE 1 TEST TUBE 2
Benedict's Test Iodine Test
Obs. Result Obs. Result
TEST TUBE 3
Biuret Test
Obs. Result
TEST TUBE 4
Sudan IV Test
Obs. Result
General Conclusions and why?
Obs. = Observed color; Result = positive or negative.
You must submit this for your TA’s approval. He/She will indicate whether your team will be allowed to leave based on your data.
HOMEWORK :
• Before coming to lab next week, make sure to read the Enzymes task sheet as well as
Chapter 10 (pgs. 111-115) in your lab manual.
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