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Essay Name       : 571.txt 
Uploader         : Eve Xin
Email Address    : 
Language         : english
Subject          : Biology
Title            : Detection of biological molecules
Grade            : A
School System    : IB/AP
Country          : USA
Author Comments  : very extensive lab...  the results should be obtained by the reader who should have the info. <it's in microsoft word chart format, couldn't get it to appear>
Teacher Comments : good style and observations... etc. etc...
Date             : 10-23-96
Site found at    : through a friend
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DETECTION OF BIOLOGICAL MOLECULES

Introduction:  Without carbon, nitrogen, hydrogen, sulfur, oxygen and phosphorus, life
wouldn't exist.  These are the most abundant elements in living organisms.  These elements
are held together by covalent bonds, ionic bonds, hydrogen bonds, and disulfide bonds. 
Covalent bonds are especially strong, thus, are present in monomers, the building blocks
of life.  These monomers combine to make polymers, which is a long chain of monomers
strung together.  Biological molecules can be distinguished by their functional groups.  For
example, an amino group is present in amino acids, and a carboxyl group can always be
found in fatty acids.  The groups can be separated into two more categories, the polar,
hydrophilic, and the nonpolar, hydrophobic.  A fatty acid is nonpolar, hence it doesn't mix
with water.  Molecules of a certain class have similar chemical properties because they
have the same functional groups.  A chemical test that is sensitive to these groups can be
used to identify molecules that are in that class.  This lab is broken down into four
different sections, the Benedict's test for reducing sugars, the iodine test for the presence
of starch, the Sudan III test for fatty acids, and the Biuret test for amino groups present in
proteins.  The last part of this lab takes an unknown substance and by the four tests,
determine what the substance is.

BENEDICT'S TEST

Introduction:  Monosaccharides and disaccharides can be detected because of their free
aldehyde groups, thus, testing positive for the Benedict's test.  Such sugars act as a
reducing agent, and is called a reducing sugar. By mixing the sugar solution with the
Benedict's solution and adding heat, an oxidation-reduction reaction will occur.  The sugar
will oxidize, gaining an oxygen, and the Benedict's reagent will reduce, loosing an oxygen. 
If the resulting solution is red orange, it tests positive, a change to green indicates a
smaller amount of reducing sugar, and if it remains blue, it tests negative.  

Materials:
onion juice		5 test tubes		1 beaker
potato juice		ruler			hot plate
deionized water	permanent marker	5 tongs
glucose solution	labels
starch solution		6 barrel pipettes
Benedict's reagent	5 toothpicks

Procedure:
1.	Marked 5 test tubes at 1 cm and 3 cm from the bottom. Label test tubes #1-#5.
2.	Used 5 different barrel pipettes, added onion juice up to the 1 cm mark of the first
	test tube, potato juice to the 1 cm mark of the second, deionized water up to the 1
	cm mark of the third, glucose solution to the 1 cm mark of the fourth, and the 
	starch solution to the 1 cm mark of the fifth test tube.
3.	Used the last barrel pipette, added Benedict's Reagent to the 3 cm mark of all 5
	test tubes and mix with a toothpick.
4.	Heated all 5 tubes for 3 minutes in a boiling water bath, using a beaker, water, and
	a hot plate.
5.	Removed the tubes using tongs.  Recorded colors on the following table.
6.	Cleaned out the 5 test tubes with deionized water.

Data:
          	Benedict's Test Results
  

Discussion:  From the results, the Benedict's test was successful.  Onion juice contains
glucose, and of course, glucose would test positive.  Starch doesn't have a free aldehyde
group, and neither does potato juice, which contains starch.  Water doesn't have glucose
monomers in it, and was tested to make sure the end result would be negative, a blue
color.  

IODINE TEST

Introduction:	The iodine test is used to distinguish starch from monosaccharides,
disaccharides, and other polysaccharides.  Because of it's unique coiled geometric
configuration, it reacts with iodine to produce a blue-black color and tests positive.  A
yellowish brown color indicates that the test is negative.

Materials:
6 barrel pipettes	potato juice		starch solution
5 test tubes		water			iodine solution
onion juice		glucose solution	5 toothpicks

Procedure:
1.	Used 5 barrel pipettes, filled test tube #1 with onion juice, second with potato
	juice, third with water, fourth with glucose solution, and fifth with starch solution.
2.	Added 3 drops of iodine solution with a barrel pipette, to each test tube.  Mixed
	with 5 different toothpicks.
3.	Observed reactions and recorded in the table below.  Cleaned out the 5 test tubes.
Data:
 Iodine Test Results


Discussion:	The iodine test was successful.  Potato juice and starch were the only two
substances containing starch.  Again, glucose and onion juice contains glucose, while
water doesn't contain starch or glucose and was just tested to make sure the test was done
properly.

SUDAN III TEST

Introduction:  Sudan III test detects the hydrocarbon groups that are remaining in the
molecule.  Due to the fact that the hydrocarbon groups are nonpolar, and stick tightly
together with their polar surroundings, it is called a hydrophobic interaction and this is the
basis for the Sudan III test.  If the end result is a visible orange, it tests positive.  

Material:
scissors	deionized water	margarine		Sudan III solution
petri dish	starch			ethyl alcohol		forceps
lead pencil	cream			5 barrel pipettes
filter paper	cooking oil		blow dryer

Procedure:
1.	Cut a piece of filter paper so it would fit into a petri dish.  
2.	Used a lead pencil, and marked W for water, S for starch, K for cream, C for
	cooking oil and M for margarine.  Draw a small circle next to each letter for the
	solution to be placed.
3.	Dissolve starch, cream, cooking oil and margarine in ethyl alcohol.
4.	Used a barrel pipette for each solution, added a small drop from each solution to
	the appropriate circled spot on the filter paper.  
5.	Allowed the filter paper to dry completely using a blow dryer.
6.	Soaked the paper in the Sudan III solution for 3 minutes.
7.	Used forceps to remove the paper from the stain.
8.	Marinated the paper in a water bath in the petri dish, changed water frequently.
9.	Examined the intensity of orange stains of the 5 spots.  Record in the table below.
10. 	Completely dried the filter paper, and washed the petri dish.

Data:
Sudan III Test Results






Filter paper:


















Discussion:  The results indicate that the Sudan III test was sucessful.  Water and starch
definitely doesn't contain any fatty substances.  Cream and cooking oil no doubtedly does
contain lipids.  It was surprising to find that margarine doesn't contain any fat.  

BIURET TEST

Introduction:  In a peptide bond of a protein, the bond amino group is sufficiently
reactive to change the Biuret reagent from blue to purple.  This test is based on the
interaction between the copper ions in the Biuret reagent and the amino groups in the
peptide bonds.  

Materials:
6 test tubes		egg white solution	starch solution		6 toothpicks
ruler			chicken soup solution	gelatin			6 parafilm sheets
permanent marker	deionized water	sodium hydroxide
labels			glucose solution	copper sulfate

Procedures:
1.	Used 6 test tubes, and labeled them at 3cm and 5cm from the bottom.  Labeled
	each #1 to #6.
2.	Added egg white solution to the 3cm mark of the first tube, chicken soup solution
	to the 3-cm mark of the second tube, water to the 3 cm mark of the third test tube,
	glucose solution to the fourth, starch to the fifth, and gelatin to the sixth, all at the
	3 cm mark.
3.	Added sodium hydroxide to the 5 cm mark of each tube and mix with 6 different
	toothpicks.
4.	Added 5 drops of  Biuret test reagent, 1% copper sulfate, to each tube and mix
	by placing a parafilm sheet over the test tube opening, and shake vigorously.
5.	Held the test tubes against a white piece of paper, and recorded the colors and
	results.  Discarded the chemicals, and washed the test tubes.

Data:
Biuret Test Results


Discussion:  The Biuret test seemed to have been successful.  Glucose and starch are both
carbohydrates, while water has no proteins.  Egg white definitely has proteins, and so does
gelatin.  Chicken soup had a hint of protein content.  

Unknown Chemical # 143

Introduction:  By performing the Benedict's Test, the Iodine Test, the Sudan III Test,
and the Biuret Test, chemical #143 should be identified.  

Materials:  
materials from the Benedict's Test		materials from the Sudan III Test
Materials from the Iodine Test		materials from the Biuret Test

Procedures:
1.	Performed the Benedict's Test, and recorded results.
2.	Performed the Iodine Test, and recorded results.
3.	Performed the Sudan III Test, and recorded results.
4.	Performed the Biuret Test, and recorded results.

Data:
Properties of Chemical #143


chemical #143 was a white powderish substance. 

Conclusion:  After ruling out the obvious wrong substances from the list  like ground
coffee, egg white and yolk, table sugar and salt, syrup and honey, the small amount of
proteins was taken into factor.  That also eliminated powdered skim milk, and soy flour. 
The low, or none fat content ruled out some more choices like enriched flour.  The only
choices left was corn starch, glucose, and potato starch.  Because of the low reducing
sugar, glucose can be ruled out also.  



The starch content of substance #143 was very high.  The protein content was around the
10% range, so potato starch would be a better guess then corn starch.  But corn starch
contained only a trace of fat when potato starch contained 0.8%.  But 0.8% is very
insignificant.  The most educated guess to what chemical #143 is potato starch.
 
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