Posted: April 25th, 2025
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Fischer projections, D and L Notations, hyperglycemia and hypoglycemia. 13.2 an 13.3
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Chemistry: An Introduction to General, Organic, and Biological Chemistry
Thirteenth Edition
Chapter 13
Carbohydrates
Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
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13.3 Fischer Projections of Monosaccharides
Glucose, galactose, and fructose are the most important monosaccharides.
Learning Goal Identify or draw the D and L configurations of the Fischer projections for common monosaccharides.
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Fischer Projections
A Fischer projection used to represent carbohydrates
places the most oxidized group at the top
shows chiral carbons as the intersection of vertical and horizontal lines
shows the
on the horizontal
intersecting line
places the
at the bottom of the Fischer
projection, which is not chiral
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D and L Notations
In a Fischer projection, the
on the
chiral carbon farthest from the carbonyl group determines an L or a D isomer
left is assigned the letter L
right is assigned the letter D
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D and L Isomers of Monosaccharides
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Learning Check 1
In the following Fischer projection of mannose, identify the monosaccharide as a D or an L isomer.
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Solution 1 (1 of 2)
In the following Fischer projection of mannose, identify the monosaccharide as a D or an L isomer.
Analyze the Problem
Given
Need
Connect
Analyze
The Problem
Fischer projection of mannose
Identify as D or L mannose
chiral carbon farthest from carbonyl group
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Solution 1 (2 of 2)
In the following Fischer projection of mannose, identify the monosaccharide as a D or an L isomer.
Step 1 Number the carbon chain, starting at the top of the Fischer projection.
Step 2 Locate the chiral carbon farthest from the top of the Fischer projection. The chiral carbon farthest from the top is carbon 5.
Step 3 Identify the position of the
as D or L. The
is on the right of
carbon 5, which makes it D-mannose.
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Learning Check 2
In the following Fischer projection,
A. identify the number of chiral centers.
B. identify the monosaccharide as a D or an L isomer.
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Solution 2
In the following Fischer projection,
A. identify the number of chiral centers.
B. identify the monosaccharide as a D or an L isomer.
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Glucose and Fructose (1 of 2)
D-Glucose is
found in fruits, corn syrup, and honey
an aldohexose with the formula C6H12O6
known as dextrose and blood sugar in the body
a building block in sucrose, lactose, maltose, and in polysaccharides such as cellulose and glycogen
D-Fructose, obtained from sucrose, is
a ketohexose with the formula C6H12O6
the sweetest of the carbohydrates, twice as sweet as sucrose
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Glucose and Fructose (2 of 2)
The sweet taste of honey comes from the monosaccharides D-glucose and D-fructose.
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Galactose
D-Galactose
is an aldohexose, C6H12O6
is obtained from the disaccharide lactose
has a similar structure to glucose
except for the
on carbon 4
In a condition called galactosemia, an enzyme needed to convert galactose to glucose is missing.
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Chemistry Link to Health: Hyperglycemia and Hypoglycemia (1 of 3)
In the body,
glucose has a normal blood level of 70–90 milligrams/deciLitre a glucose tolerance test measures blood glucose for several hours after ingesting glucose
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Chemistry Link to Health: Hyperglycemia and Hypoglycemia (2 of 3)
Diabetes mellitus can cause hyperglycemia, which
occurs when the pancreas is unable to produce sufficient quantities of insulin
allows glucose levels in the body fluids to rise as high as 350 milligrams/deciLitre of plasma
Symptoms of diabetes include
thirst and excessive urination
increased appetite and weight loss
In older adults, diabetes is sometimes a consequence of excessive weight gain.
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Chemistry Link to Health: Hyperglycemia and Hypoglycemia (3 of 3)
When a person is hypoglycemic,
the blood glucose level rises and then decreases rapidly to levels as low as 40 milligrams/deciLitre
low blood sugar may occur as a result of an overproduction of insulin by the pancreas
symptoms may appear, such as dizziness, general weakness, and muscle tremors
a diet may be prescribed that consists of several small meals high in protein and low in carbohydrates
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Learning Check 3
Draw the Fischer projections of D-fructose and L-fructose.
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Solution 3
Draw the Fischer projections of D-fructose and L-fructose.
D-Fructose
L-Fructose
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Copyright
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