Transcript Cell structure and function

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All living organisms are composed of four classes of
macromolecules:
 Carbohydrates
 Lipids
 Proteins
 Nucleic acid
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 Carbon containing compounds are called organic compounds.
 Carbon is the backbone of organic molecules, but its only one
of several important bioelements.
 These
bioelements are
phosphorous and sulfur.
hydrogen,
nitrogen,
oxygen,
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 The chemical properties of the different classes depend on the
presence of specific functional groups:
 Aldehyde group

Ketone group

Carboxyl group
 Amino group
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Identification of Carbohydrates
 Carbohydrates are the main energy storing molecules.
 Monosaccharide : monomers (glucose, ribose, galactose).
 Disaccharides: two monomers connected with glycosidic
bond  (sucrose, lactose).
 Polysaccharides: polymers; more than three monomers
(starch).
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Identification of carbohydrates
A. Benedict’s test for reducing sugars:
 The test depends on the presence of free Aldehyde or
ketone group.
 Monosaccharides and some disaccharides have these groups
free are called reducing sugars.
 Free groups found in reducing sugars will react with
Benedict’s reagent (CuSo4 which is blue in color with
NaOH).
 The test is both qualitative and quantitative test;

Small amount of reducing sugar  green color.

Large amount of reducing sugar  red- orange color.
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Procedure:
 Label 7 clean test tubes
(1-7)
 Fill the test tubes with 1 ml of
one of the following solutions.
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 Fill each test tube with
Benedict’s reagent
3 ml of
 Put the test tubes in boiling water for 5 minutes
 If color change to:
 Yellow
 Orange
 Red
Green
Positive test for reducing.
 If color remains blue
(the color of Benedict’s reagent)
Negative result.
 Record your results in a proper table
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B. Lugol’s iodine test for starch
 Starch is a polysaccharide consisting of many glucose
monomers linked together into long branching chains.
 It is the primary storage carbohydrate in plants.
 In the presence of iodine (I2-KI), a solution containing
starch will turn blue-black in color.
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Procedure:
 Label 7 clean test tubes
(1-7)
 Fill the test tubes with 2 ml of
one of the following solutions.
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 Add two drops of lugol’s iodine to each
test tube.
 If color change to:
 A blue-black
 If color remains yellow - brown
(the color of the iodine)
Positive test for starch
Negative result.
 Record the result in the report.
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Identification of Proteins
 Proteins are the key substances in the structural and
physiological function of living things.
 Proteins are polymers of amino acids in which the carboxyl
group of one amino acid is linked with the amino group of the
next amino acid in a covalent bond called the peptide bond.
A. Ninhydrin test for amino acids
 Ninhydrin reagent reacts with free amino groups i.e free
amino acids to form a purple or violet colored substance.
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 Ninhydrin reagent can also be used to detect proteins, but they
must be heated or digested to hydrolyze the protein into free
amino acids.
Procedure
 label 4 clean test tubes (1-4)
 Fill the test tubes with 2 ml of one of the following solutions:
1) Albumin solution.
2) Milk.
3) Amino acid solution (Lysine).
4) Distilled water.
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 To each of the test tubes, add 10 drops of ninhydrin reagent
and heat the test tubes in boiling water for 5 minutes (avoid
inhaling, poisonous fumes).
 A purple color is the +ve result.
 Record the color of the tubes
content in the lab report.
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B. Biruet test for polypeptides
 The test reveals the presence of peptide bond i.e. proteins
 Biuret reagent CuSo4 reacts with the peptide bonds between the
amino acids changing in color from light blue to violet under
alkaline conditions.
 The intensity of the violet color is proportional to the protein
concentration.
 In the test, Cu+2 must complex with at least four to six peptide
bonds to produce a color.
 Biuret

reagent does not react with free amino acids.
Short peptides don’t react positively.
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Procedure:
 Label 5 clean test tubes
(1-5)
 Fill the test tubes with 2 ml of
one of the following solutions.
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 Fill each test tube with 2 ml of Biuret
reagent
 If color change to:
 Violet
Positive test for Biuret test
 If color remains blue (the color
of Biuret reagent).
Negative result.
Record your results in a proper table.
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Identification of lipids
 Lipids are a heterogeneous group of compounds that are
insoluble in water, but are soluble in organic solvents such as
ether and acetone.
 There are three major classes of lipids:



Neutral fats (triglycerides).
Phospholipids
Steroids
A. Sudan red test for fats
 Sudan red is a lipid soluble dye, when added to a mixture of
lipids and water, The dye will move into the lipid layer
giving the lipid a red color.
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Procedure
 Fill the test tube with 2ml of Water .
 Add 10 drops of oil and mix.
 The two liquids do not mix after shaking the test tube,
because the oil molecules are hydrophobic (insoluble in
water) to produce an emulsion.
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 Add 10 drops of Sudan IV solution
to the test tube and mix.
 Two layers are formed, the upper
one is the lipid stained with Sudan red IV
 The water remains in the bottom layer
 Record your observations.
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