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Chemical composition of cells
Lab 3
Introduction
Inorganic molecules
nonliving things
Organic molecules
living organisms
Salt molecules: NaCl (Sodium chloride Na+ Cl-)
Sugar
Organic compounds in living thing
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Proteins
Carbohydrates
Lipids
Nucleic acids
Concepts
• A monomer is a molecule that may bind chemically to
other molecules to form a polymer.
• A polymer is a large molecule (macromolecule) composed
of repeating structural units.
• Proteins and some carbohydrates are polymers.
• Dehydration reactions— smaller molecules bond as
water is given off
• Hydrolysis reactions— bonds are broken as water is
added
Control
Positive control—goes through all the steps of the
experiment and does contain the substance being
tested (positive results are expected)
Negative control—goes through all the steps of the
experiment except it does not contain the substance
being tested (negative results are expected)
• The control samples usually validate the
experiment. If negative control samples give
positive results, the experiment is invalid—the
reagents may be contaminated or the procedure
may need improvement.
Carbohydrate
• Carbohydrate— sugars and chains of sugars
• Glucose— monomer – monosaccharide
• Maltose— 2 sugar unit – disaccharide
• Glycogen, Starch ect.—chains of glucose
units—polysaccharides
Tests for carbohydrates
• Test for starch (page29)
if starch is present
Iodine— brown →blue;
if starch is absent
Iodine— no color change
Which tube is the control?
• Test for sugars (page31)
Benedict’s reagent reacts with small sugar molecules
(glucose, maltose etc.) after heating — blue →
green/yellow/red
!! Highly corrosive
Which tube is the control?
Protein
• Amino acid (Aa)
• ~20 different common
amino acids
• ＞10 Aa = polypeptide amino group (-H N)
acidic group (-COOH)
• ＞50 Aa = protein
• antibodies, transport proteins (hemoglobin, albumin),
regulatory proteins (insulin); structural proteins
(keratin— hair, myosin—muscle); enzyme (speed
chemical reactions)
2
Test for protein
Biuret reagent (NaOH+CuSO4 ) page 33
Peptide bonds combine with the copper ions.
blue→ purple
!! Highly corrosive
Which tube is the control?
Lipids
Emulsification of Lipids
• Emulsifier can cause a fat to disperse in water
Today’s tests
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Test for Fat Page 35 15 min
Chemical composition unknown A and B
Test for sugars Page 31 5-10 min
Chemical composition unknown A and B
Emulsification of Lipids Page 36 5 min
Test for proteins Page 33
Chemical composition unknown A and B
Test for starch Page 29
Chemical composition unknown A and B
Microscopic observation* Page 30
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