Chemical Composition of Cells - Biological
Molecules
Bio 107; Week 3
Lab Activities
• Testing for Biological Molecules
–Carbohydrates
–Proteins
–Lipids
Learning Goals
• Distinguish between positive and negative controls and
between positive and negative results. Know how to use both
positive and negative controls.
• Explain the results of the Benedict’s test, Iodine test, Biuret
test.
• Know the major macromolecules found in cells, their functions,
and what they are made of.
Biological Molecules
•
•
•
•
Carbohydrates
Proteins
Lipids
Nucleic Acids
• Carbohydrates = Energy!
• C6H12O6
Monosaccharides or
Simple Sugars
• “Ready energy”
• Used by
mitochondria in
cells to produce
ATP
• C6H12O6
Disaccharides
• Sucrose
Dehydration Synthesis
Reaction
Polysaccharides
• Function: Storage, structural
• Why are polysaccharides used
as storage molecules?
Polysaccharides
• Chains of glucose
produced by plants:
starch
Polysaccharides
• Glycogen: branching
chain of glucose.
Polysaccharides
• Plants use cellulose as
structure.
• “Dietary fiber”
Testing for Carbohydrates:
Monosaccharides and
Benedict’s Test
• Glucose and fructose =
“Reducing sugars” – can
take electron from copper
in Benedict’s reagent.
• Sugars reduce Cu2+ to Cu+
Cu2+ (blue)
Boiling water bath, 3 min
Cu+ (reddish orange)
Testing for Carbohydrates:
Polysaccharides and the
Iodine Test
• Starch structure: coiled
polysaccharide
• I2KI : iodine-potassium
iodide.
Testing for
Carbohydrates
Table 6.1: Solutions and color reactions for reducing sugars and iodine
test for starch
Controls
Negative Control – does not
contain the variable for
which you are searching.
Expect negative results;
show you what a negative
result looks like.
Tube
1
10 drops onion juice
2
10 drops potato juice
3
10 drops sucrose
solution
4
10 drops glucose
solution
5
10 drops distilled
water
6
10 drops reducingsugar solution
10 drops starch
solution
7
Solution
Benedict’s Color
Reaction
Iodine Color
Reaction
Testing for
Carbohydrates
Table 6.1: Solutions and color reactions for reducing sugars and iodine
test for starch
Controls
Positive Control – contains
the variable for which you
are testing; reacts positively,
shows that test can detect
what you expect.
Tube
1
10 drops onion juice
2
10 drops potato juice
3
10 drops sucrose
solution
4
10 drops glucose
solution
5
10 drops distilled
water
6
10 drops reducingsugar solution
10 drops starch
solution
7
Solution
Benedict’s Color
Reaction
Iodine Color
Reaction
Testing for Proteins: Biuret Test
• Chains of amino acids
Testing for Proteins: Biuret Test
• Chains of amino acids
• Connected by peptide bonds (C-N)
• Proteins = long chains of amino acids
Testing for Proteins: Biuret Test
•
•
•
•
Biuret reagent: CuSO4 (Copper sulfate)
Cu2+ forms complex with peptide bonds
Complex is violet in color
Would amino acids in solution produce
violet color? Why or why not?
Testing for Proteins: Biuret Test
Table 6.2: Solutions and color reactions for the Biuret Test for Proteins
Tube
Color
1
2 mL egg
albumen
2
2 mL honey
3
2 mL amino
acid solution
4
2 mL distilled
water
5
2 mL protein
solution
Protein present? (Y/N)
Lipids - Solubility
• Non-polar
Lipids - Solubility
• Triglycerides
– Three fatty acid tails
– One glycerol
Exercises
After color observations, put
inference (+/- or Y/N)
• Procedure 3.1 – Carbohydrates
– Iodine test for starch
– Benedict’s test for reducing sugars
– Observe potato and onion under microscope (skip if short on time)
• Procedure 3.2 – Biuret test for protein (Swap pepsin for honey;
use amino acid and protein found up front)
• Procedure 3.3 – Test for Fat
• Test Unknown (Can skip, but will be on quiz!)
Pour solutions down sink; rinse test tubes, put in rack by sink