Carbohydrates play an important role in living organisms. They are classified as simple or complex sugars and serve as a primary energy source. The most common simple sugars are monosaccharides like glucose, fructose, and galactose. Complex carbohydrates are made of two or more linked monosaccharides and include disaccharides like sucrose and polysaccharides like starch and cellulose. Carbohydrates have many functions in biochemistry such as energy storage, structure in plants, and determining blood types in humans.

1. Carbohydrates
Brittany Northcutt
5 May 2013
CHE-150-5001

2. “Carbohydrates occur in every living organism. The sugar and starch in food,
and the cellulose in wood, paper, and cotton are nearly pure carbohydrates”
(McMurry 2011). There are some carbohydrates that are used in medicine as well as
some are a coating to our cells and others are part of the nucleic acid around our
DNA. The first carbohydrate that was known to be pure was glucose. Its molecular
formula is C6H12O6 and was known as the “hydrate of carbon”. Dextrose is often the
medical term that is used when referring to glucose.
During photosynthesis, green plants synthesize carbohydrates in a difficult
process which sunlight converts CO2 andH2O into glucose plus oxygen. Cellulose or
starch is what the plant uses for molecules of glucose to be chemically linked for
storage. Once animals eat and metabolize carbohydrates, they then have plenty of
stored energy readily available. Carbohydrates act as chemical intermediaries
where the solar energy is stored there and used when needed to support life.
Carbohydrates can be classified as either simple or complex sugars. Simple
sugars are also known as monosaccharides and they are carbohydrates that can’t be
converted into smaller sugars by hydrolysis. Examples of these simple sugars are
glucose and fructose. “Complex carbohydrates are made of two or more simple
sugars that are linked together” (McMurry 2011). An example of complex
carbohydrates is sugar which is what we know as table sugar.
Monosaccharides are classified as either aldoses or ketoses. The suffix –ose
classifies it as a carbohydrate and the aldo- or keto- prefixes classify the molecule as
either an aldehyde or ketone. The different numerical prefixes will be added as well

3. based on the number of carbon atoms. The most common simple sugars are
aldopentoses and aldohexoses.
Carbohydrates have many chirality centers and was used as a quick method
to represent stereochemistry. Carbohydrate chemistry uses a lot of Fischer
projections to show the chirality centers and represent the stereochemistry.
Tetrahedral carbon atoms are represented by two crossed lines; horizontal lines
showing coming out of the page while vertical lines represent going into the page.
Most carbohydrates have more than one chirality center and once represented by
Fischer projections, the centers are stacked on top of one another with the carbonyl
carbon all the way at the top.
D and L sugars are optical isomers of each other, or non-superimposable
mirror images. D is for dextrorotatory enantiomers which occur naturally and L is
for levorotatory for the mirror image of the corresponding D sugars which has
opposite configurations at all chirality centers. D sugars have a R configuration
while L sugars have a S configuration. A D sugar can either be dextrorotatory or
levorotatory because the D prefix shows the stereochemistry of the lowest chirality
center. “Aldotetroses are four-carbon sugars with two chirality centers,
aldopentoses have three chirality centers, and aldohexoses have four chirality
centers.” (McMurry 2011).
“When an open-chain monosaccharide cyclizes to a pyranose or furanose
form, a new chirality center is generated at the former carbonyl carbon. Two
diastereomers, called anomers, are produced, with the hemiacetal carbon reffered
to as the anomeric center.” (McMurry 2011). An alpha anomer is a minor anomer

4. which has a C1 –OH group trans to the –CH2OH substituent at C5. A beta anomer is a
major anomer which has the C1 –OH group cis to –CH2OH substituent at C5. Both of
the anomers can be crystallized and purified. When a sample of pure anomer is
dissolved in water, the optical rotation slowly changes and reaches a constant value
of +52.6 which is the specific rotation of alpha anomers.
Monosaccharides behave as simple alcohols in their chemistry. They often
form syrups which result in it to be difficult to purify rather than crystals. Crystals
are easier to be removed in water. Ester and ether are soluble in organic solvents
and are purified and crystallized easily. Treating a carbohydrate with an acid
chloride or acid anyhydride in the presence of a base is known as esterification. This
includes all of the –OH groups.
When treated with an alkyl halide with the presence of a base, carbohydrates
are then converted into ethers. Silver oxide is the one that is most used for this.
Hydroxide and alkoxide bases have a tendency to tear apart the sensitive sugar
molecules.
Carbohydrate acetals are named by first citing the alkyl group and then
replacing the –ose ending of the sugar with –oside is known as glycosides. Since a
glycoside is an acetal, it is very stable in water. Glycosides are often very important
in nature and contain important biological glycosidic linkages.
“In living organisms, carbohydrates occur not only in their free form but also
linked through their anomeric center to other biological molecules such as lipids or
proteins” (McMurry 2011). When a reaction of the lipid or protein with a glycosyl
nucleoside diphosphate occurs, it is known as a glycoconjugate formation. The

5. diphosphate then forms with ATP to create uridine triphosphate. The purpose of
this is to make a better leaving group for the nucleophilic substitution reaction with
a protein or lipid and activate the anomeric –OH group.
An alditol is the treatment of an aldose or a ketose with NaBH4 reduces it to a
polyalcohol. An open chain reaction will occur when the reaction is present in the
aldehyde. D-Glucitol is a substance that has been isolated from many fruits and
berries and is known as D-sorbitol and is used in many foods as a sweetener and
sugar substitute.
Aldonic acids are aldoses that can be oxidized to yield the corresponding
carboxylic acids. “Aldoses are reducing sugars because they contain aldehyde
carbonyl groups, but glycosides are nonreducing because the acetal group can’t
open to an aldehyde under basic conditions” (McMurry 2011). An aldaric acid is if a
warm dilute HNO3 is used as the oxidizing agent, an aldose is oxidized to a
dicarboxylic acid.
Eight monosaccharides are needed for humans for proper functioning. You
can receive most of these monosaccharides efficiently in your diet. The eight
monosaccharides are L-fucose, D-galactose, D-glucose, D-mannose, N-acetyl-D-
glucosamine, N-acetyl-D-galactosamine, D-xylose, and N-acetyl-D-neuraminic acid.
These are all the body’s primary source of energy and is used in the synthesis of the
glycoconjugate components of cell walls and glucose. Galactose, glucose, and
mannose are the simple aldohexoses while xylose is an aldopentose of the eight
monosaccharides.

6. An anomeric carbon can either be an alpha or beta glycoside acetal bond
between one sugar and an –OH group at any place on the sugar. “Maltose and
cellobiose are both reducing sugars because the anomeric carbons on the right-hand
glucopyranose units have hemiacetal groups and are in equilibrium with aldehyde
forms” (McMurry 2011). Cellobiose and maltose have very different properties
biologically. Cellobiose can’t be digested by humans or fermented by yeast and
maltose is digested easily and readily fermented.
Sucrose is known as the table sugar we use on a day-to-day basis and is also
known as the most abundant pure organic chemical in the world. No matter where
the sugar is from, it is always from sucrose. Sucrose is also not a reducing sugar and
honey is primarily a mixture of glucose, fructose, and sucrose. 1 equivalent of
glucose and 1 equivalent of fructose on hydrolysis is because sucrose is a
disaccharide.
Polysaccharides are not reducing sugars and don’t show noticeable
mutarotation. The two most widely occurring polysaccharides are cellulose and
starch. Cellulose interact to form a large structure and stay connected together by
hydrogen bonds. It is also a material that used for the strength and rigidity in plants.
Starch is a large amount in potatoes, corn and cereal grains. Starch is often
separated into amylose and amylopectin. Amylose accounts for 20% and
amylopectin accounts for 80%.
Carbohydrates have many important biochemical functions. Humans blood
can be classified into four different types; A, B, AB, and O. If the two types are
compatible, the blood from the donor will then be transfused into the recipient. If

7. they are not compatible, agglutination will occur. Agglutination is when an
incompatible mix is made and the red blood cells clump together. This means that
the body’s immune system recognizes foreign cells in the body and form antibodies
against them.

8. Works Cited
McMurry, John E. Fundamentals of Organic Chemistry. 7th ed. Belmont , CA:
Brooks/Cole, 2011. Print.