Lab 3

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Lab 3
Organic Molecules
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The large molecules in three of the four classes
of organic compoundscarbohydrates, proteins, and
nucleic acidsare chain-like molecules called
polymers
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A polymer is a long molecule consisting of many
similar or identical building blocks that are
linked together by covalent bonds
The individual building blocks are called monomers
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Some of the molecules that serve as monomers also
have important functions of their own For
instance, the monosaccharide glucose exists in
the form of a single molecule
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The classes of polymeric macromolecules differ in
the nature of their monomers, but the chemical
mechanisms that cells use to make and break
polymers are basically the same in all cases
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Monomers are connected by a reaction in which two
molecules are covalently bonded to each other
through loss of a water molecule this is called
a condensation or dehydration reaction
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When a bond forms between two monomers, each
monomer contributes part of the water molecule
that is lost One molecule provides a hydroxyl
(OH-) group, while the other provides a hydrogen
(H-)
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Functional Groups
These functional groups that are attached to
organic molecules determine the chemical
reactivities of those molecules
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Carbohydrates include both sugars and their
polymers. The simplest carbohydrates are the
monosaccharides, or single (simple) sugars
Disaccharides are double sugars consisting of two
monosaccharides
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Monosaccharides generally have molecular formulas
that are some multiple of
If we look at the structure of glucose, we can
see the trademarks of a sugar
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The molecule has a carbonyl group and multiple
hydroxyl groups. In aqueous solutions, glucose
molecules form rings
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Depending on the location of the carbonyl group,
a sugar is either an aldose (aldehyde sugar) or a
ketose (ketone sugar). Glucose is an aldose
fructose, a structural isomer of glucose, is an
aldose
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A disaccharide such as sucrose consists of two
monosaccharides joined by a glycosidic linkage,
which is a covalent bond formed between two
monosaccharides by a dehydration reaction
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Glycosidic Linkage
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Starch, a storage polysaccharide of plants, is a
polymer consisting entirely of glucose monomers.
Most of these monomers are joined by14 carbon
linkages, which makes the polymer helical
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We will be using Benedicts reagent to test for
the presence of reducing sugars. These are sugars
with free aldehyde or ketone groups that will
react with the reagent to form a colored
precipitate
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If the reactive aldehyde or ketone groups are
involved in the bond that joins the
monosaccharide units, as in sucrose, the
disaccharide will not react with Benedicts
reagent
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Reactive Hydroxyl Group
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Starch will not show a reaction with Benedicts
reagentThe number of free aldehyde groups, found
only at the ends of the chain, is small in
proportion to the rest of the molecule
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Lipids
Lipids include fats, steroids, and phospholipids
Today we will be focusing on fats. Remember that
lipids are not polymers, they are large
biological molecules that exist singly
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We will be testing for lipids today. The point of
exercise B in the lab is to distinguish between
lipid and non-lipid substances using the Sudan IV
test
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Proteins and Amino Acids
Proteins are the most structurally sophisticated
molecules known, and all are polymers constructed
from the same set of 20 amino acids. Polymers of
amino acids are called polypeptides
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Amino acids are organic molecules possessing both
carboxyl groups and amino groups
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Polypeptides are chains of amino acidsThe
peptide bonds formed between the carboxyl group
of one amino acid to the amino group of the next
happens by means of a dehydration reaction
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Today we will be testing for proteins and amino
acids the objective is to distinguish between
free amino acids and proteins on the basis of
their ability to react with either biuret reagent
or ninhydrin
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The biuret reagent is used in the biuret protein
assay, which is a chemical test for proteins
Ninhydrin is a chemical that can be used to
detect ammonia or amino acids
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The variable that we, as investigators, are
manipulating is called the independent variable
The dependent variable is the response we expect
to get
Our null hypothesis predicts that there will be
no response at all
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Web Resources
Chemistry for Biologists
http//www.chemsoc.org/networks/learnnet/cfb/index
.htm
Virtual Textbook of Organic Chemistry
http//www.cem.msu.edu/reusch/VirtualText/intro1.
htm