SAN DIEGO MESA COLLEGE
Intro to Molecular & Cellular Biology Laboratory (Bio210a)
Instructor: Elmar Schmid, Ph.D.
Lab Summary Questions & Exercises
________________________
(Student Name)
(Completion of the summary questions below are a mandatory part of your weekly lab
report; answer the questions below and turn the stapled sheets back to your instructor at
the beginning of the next lab session)
Q. 1: Which part of the sugar actually reacts with Benedict’s reagent? Make a drawing to
show the actual chemical reaction of the Benedict’s reagent with the critical functional group
of the reactive sugar.
Q. 2: Why does starch (under testing conditions) not react with Benedict’s reagent and show a
color change?
Q. 3: Under which circumstances or experimental conditions (if at all) would you expect a
reaction of Benedict’s reagent with starch? Describe an experimental set-up which would lead
to a positive reaction of starch with Benedict’s Reagent.
Q. 4: Would you expect a reaction of acid (HCl)-treated paper (cellulose) with Benedict’s
reagent? Why or why not!
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SAN DIEGO MESA COLLEGE
Intro to Molecular & Cellular Biology Laboratory (Bio210a)
Instructor: Elmar Schmid, Ph.D.
Q. 5: You examine an acid-hydrolyzed protein solution with the Benedict’s reagent and – after
performing the test – and find a positive reaction (= color change) with this sample. What
happened? How would you interpret this surprising experimental finding?
(Hint: Think of post-translational modification of proteins)
Q. 6: Describe in your own words the chemical reaction of Lugol’s Reagent with starch and
discuss the specificity of this reagent regarding polysaccharides.
Q. 7: What is the major ingredient of Lugol’s reagent?
A) potassium
B) iodoacetamide
C) iodine
D) indophenol
E) phenolred
Q. 8: You observe with a sample withdrawn from a starch solution that Lugol’s Reagent
surprisingly does not lead to a color change even though the same amount of a sample
withdrawn two hours earlier (and tested at the same temperature and conditions) showed a
strong reaction with the starch-reactive reagent. Explain this finding.
The presence of which of the following enzymes (as a contaminant in the starch solution) or
conditions may explain the experimental finding described under 8.)
A) cellulase contamination
B) amylase contamination
C) beta-glucosidase contamination
D) the starch solution was heated at high temperature after withdrawal of the first sample
E) hemicellulase contamination
F) any of the above
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SAN DIEGO MESA COLLEGE
Intro to Molecular & Cellular Biology Laboratory (Bio210a)
Instructor: Elmar Schmid, Ph.D.
Q. 9: List the substances which did not react the with Sudan IV dye and explain your findings.
Why and how does Sudan IV work as an indicator dye for fats?
Q. 10: Look at the chemical structures below and answer the following questions:
H3C
1
COOH
H3C
2
COOH
b
H2C
OH
HC
OH
H2C
OH
4
H3C
3
COOH
a
O
H3C C
O
H3C
CH2OH
OH
O
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a. Which of the following molecules show(s) (a) fatty acid(s)? Name it/them.
___________________________________________________________
b. Which molecules above show (a) lipid(s)?
___________________________________________________________
c. Which of the following molecules depict an unsaturated fatty acid?
___________________________________________________________
d. Which ones is/are unsaturated fatty acids?
___________________________________________________________
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SAN DIEGO MESA COLLEGE
Intro to Molecular & Cellular Biology Laboratory (Bio210a)
Instructor: Elmar Schmid, Ph.D.
e. Which of the molecules above are used by cells to build up a fat molecule? Draw the end
result of the chemical reaction leading to a fat molecule. Circle or high-light the functional
groups involved in the chemical reaction.
f. What is the name of the molecule shown above depicted by number 5? Mark the lipophilic and hydrophilic sections of this molecule using two different colored high-lighting
markers.
____________________________________________________________________
g. Is molecule 5 a lipophilic molecule. Argue your answer. Would molecule 5 react with
Sudan IV dye?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
Q. 11: You are involved in a clinical study which investigates the effect of an investigative antiobesity drug on humans. You want to see whether the drug lead to a reduction of fat deposits
in the test persons over the investigative time period. Which of the following tissue samples,
cell types and test dye would you use and examine to answer your question.
A) muscle tissue – myocyte – Lugol’s reagent
B) fat tissue – adipocyte – Biuret Reagent
C) fat tissue – adipocyte – Sudan Red or Sudan IV
D) nervous tissue – neurons – Sudan Red or Sudan IV
E) blood – erythrocyte – Benedict’s Reagent
Q. 12: What did you learn about the specificity of the Biuret reagent?
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SAN DIEGO MESA COLLEGE
Intro to Molecular & Cellular Biology Laboratory (Bio210a)
Instructor: Elmar Schmid, Ph.D.
Q. 13: You examine a freshly extracted solution from a newly discovered tropical fruit for the
presence of proteins and observe a strong purple color change in the presence of Biuret
reagent. You leave the solution on the bench and repeat the experiment the next day again to
confirm your earlier finding. To your surprise you only get a very weak pinkish color reaction
after addition of Biuret reagent to your solution. What happened? Explain this finding and
come up with (a) solution(s) to avoid an experimental outcome like this in future experiments.
Q. 14: Would the use of Coomassie Blue stain instead of Biuret reagent have avoided the
problem encountered under Q. 13? Argue your answer.
Q. 15: With which part (functional group) of an amino acid does Ninhydrin react during the
heating step of the procedure?
A) the carboxyl group
B) the amino group
C) the hydroxyl group
D) the R-group
Q. 16: Is Ninhydrin able to react with any part of a polypeptide chain? If yes, with which part?
If yes, why can Ninhydrin reagent NOT be used as a protein staining dye? Argue.
Q. 17: Ninhydrin reacts with a solution of an amino acid mixture and turns the liquid purple.
Could proline be one of the amino acids in the mixture?
Yes _______ , because ___________________________________________
No
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SAN DIEGO MESA COLLEGE
Intro to Molecular & Cellular Biology Laboratory (Bio210a)
Instructor: Elmar Schmid, Ph.D.
Q. 18: How could you find out whether the amino acid mixture in Q. 17: contained proline?
Q. 19: Several individual unknowns are tested to determine the type of molecules present in
the samples. Given the completed results table below, indicate whether unknowns 1 through 5
contain protein, reducing sugars, starch, lipid or free amino acid (+ = positive result =
molecule present)
Results Table
Sample
Benedict’s
Reagent
Lugol’s
Reagent
Biuret
Test
Ninhydrin
Test
Sudan IV
Test
+
-
+
-
+
+
+
+
-
1
2
3
4
5
Answer
(Molecules present)
Q. 20: An FDA lab examines the claimed fat-free and low calorie product of a food company
and receives following test results (see Table below).
(+ = positive result = molecule present)
Results Table
Sample
Benedict’s
Reagent
Lugol’s
Reagent
Biuret
Test
Ninhydrin
Test
Sudan IV
Test
1
+
+
-
-
-
Is the food product free of fat? Argue your answer.
Do you think the food product is a low calorie food source? Argue your answer.
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SAN DIEGO MESA COLLEGE
Intro to Molecular & Cellular Biology Laboratory (Bio210a)
Instructor: Elmar Schmid, Ph.D.
Q. 21: You are member of a nutritional analysis lab team which examines the product of two
different company (A and B) which both claim to have pure high protein-made products
(product A and Product B) they plan to sell to fitness stores to support fast muscle build-up in
athletes. The lab investigations using the indicated reagents and tests below obtain following
results for both products.
Results Table
Product
Benedict’s
Reagent
Lugol’s
Reagent
Biuret
Test
Ninhydrin
Test
Sudan IV
Test
A
Blue
Black-blue
Violet
Clear
B
Orange
yellow
Violet
Light Purple
No
precipitate
No
precipitate
Do both products as claimed contain protein? Why or why not.
Do the examined product contain other molecule types other than protein?
If yes, which one(s)?
Product A: __________________________________________________
Product B: __________________________________________________
Does any of the products under investigation contain amino acids? If yes, which one?
If they haven’t intentionally been added by the company, what might be the reason(s) that
this (or these) product(s) contain amino acids? Argue.
Q. 22: Some amino acids are called essential amino acids. What does this mean and which ones
are these?
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SAN DIEGO MESA COLLEGE
Intro to Molecular & Cellular Biology Laboratory (Bio210a)
Instructor: Elmar Schmid, Ph.D.
Q. 23: Which foods are rich in essential amino acids? Which ones not?
Q. 24: Fatty acids that have one or more double bonds in their hydrocarbon chain are referred
to as (Circle the correct answer!)
A) saturated fatty acids
B) unsaturated fatty acids
C) trans fatty acids
D) complex fatty acids
E) phospholipids
Q. 25: Animals (and humans) cannot make fatty acids with more than one double bond or socalled poly-unsaturated fatty acids (PUFAs), despite the fact that PUFAs are crucial
components of important animal and human structures and hormones, e.g. prostanoids. What
are good sources for the essential PUFAs in the human diet?
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SOUTHWESTERN COLLEGE
School of Mathematics, Science & Engineering
Intro Molecular & Cellular Biology Lab (BIO 211): Instructor: Elmar Schmid, Ph.D.
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