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Lab 3
carbohydrates
Monosaccharides
3
Disaccharide Formation
4
Glycogen: a Polysaccharide
It represents a storage
form of glucose.
Glycogen synthesis and
degradation occurs
primarily in the liver
and in the skeletal
muscle, although other
tissues (e.g., cardiac
muscle) may store
smaller quantities.
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How the Body Uses Sugars
Glycogen exists in the body as a reservoir of available
energy that is stored in the chemical bonds within individual
glucose monomers.
Hydrolysis of glycogen, as occurs during periods of fasting,
leads to release of the glucose monomers into the blood,
thereby preventing blood glucose from decreasing to
dangerously low levels.
Glucose is often called “blood sugar” because it is the major
monosaccharide found in the blood.
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How do we determine if
carbohydrates are present in a
solution?
A molecule is oxidized if it loses an electron or hydrogen
atom and is reduced when it gains an electron or hydrogen
atom.
Collectively, the two processes are referred to as a redox
reaction because when one molecule is oxidized, another is
reduced.
How do we determine if
carbohydrates are present in a
solution?
• Benedict’s reagent
• Tests for the presence of reducing sugars.
– Sugars that contain aldehyde groups that are
oxidized to carboxylic acids.
• Benedicts reagent (CuSO4 / citrate)
– They are classified as reducing sugars since they
reduce the Cu2+ to Cu+ which forms as a red
precipitate, copper (I) oxide.
How do we determine if carbohydrates
are present in a solution?
– Aldehydes, RCHO, can be oxidized to carboxylic
acids, RCO2H,under aqueous conditions.
REDUCING SUGARS
• All common monosaccharides are reducing
sugars.
• The disaccharides maltose and lactose are
reducing sugars.
• The disaccharide sucrose is a non-reducing
sugar.
Lugol’s Iodine (IKI) test for the
presence of starch
• Iodine dissolved in an aqueous
solution of potassium iodide reacts with starch producing a
deep blue-black color.
• This reaction is the result of
the formation of polyiodide
chains from the reaction of
starch and iodine.
• The amylose, or straight chain
portion of starch, causes the
dark blue/black color. The
amylopectin, or branched
portion of starch, causes the
formation of an orange/yellow
hue.
Proteins
Proteins
Proteins account for about 50 percent of the
organic material in the body (17 percent of the
body weight), and they play critical roles in almost
every physiological process.
Proteins are composed of carbon, hydrogen, oxygen,
nitrogen, and small amounts of other elements,
notably sulfur. They are macromolecules, often
containing thousands of atoms.
14
Proteins are Made of Amino Acids
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Peptide Bonds
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How do we test for peptides in solution?
Biuret test
Copper and base
The Biuret reagent, regularly colored blue, is used to identify
proteins. When the copper ions (Cu2+) in the reagent interact
with peptide bonds, a violet color is produced.
Ror the interaction between Cu2+ and the peptide bonds to result
in a color change, a minimum of 4-6 peptide bonds is required.
Lipids
Lipids are molecules composed predominantly (but not
exclusively) of hydrogen and carbon atoms.
These atoms are linked by nonpolar covalent bonds. Thus,
lipids are nonpolar and have a very low solubility in
water.
Lipids can be divided into four subclasses: fatty acids,
triglycerides, phospholipids, and steroids.
Lipids are important in physiology partly because some of
them provide a valuable source of energy. Other lipids are a
major component of all cellular membranes, and still others
are important signaling molecules.
Test for Fats (lipids)
Sudan IV
Like lipids, the chemical Sudan IV is not
soluble in water; it is, however, soluble in
lipids.
In this test dark red Sudan IV is added to
a solution along with ethanol to dissolve
any possible lipids.
If lipids are present the Sudan IV will
stain them reddish-orange (positive
test).
Nucleic Acids
Nucleotides
22
How do we test for the presence of
nucleic acids in solution?
• Dische diphenylamine test
– DNA can be identified chemically
with the Dische Diphenylamine test.
– Acidic conditions convert
deoxyribose to a molecule that binds
with diphenylamine to form a blue
complex.
– The intensity of the blue color is
proportional to the concentration of
DNA.
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