General organic and biological chemistry structures off life 5th CH15 carbohydrates GOB structures 5th ed

Lecture Presentation

Chapter 15
Carbohydrates

Karen C. Timberlake
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chapter 15 Carbohydrates
Diabetes nurses help patients
• learn to monitor their
medication and blood
sugar levels.
• look for symptoms like
diabetic nerve damage and
vision loss.
This requires knowledge of
the endocrine system, as this
system is often involved with
obesity and other diseases.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chapter 15 Readiness

Core Chemistry Skills
• Naming Alcohols and Phenols (13.1)
• Writing Equations for the Oxidation of Alcohols (13.4)
• Naming Aldehydes and Ketones (14.1)

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


15.1 Carbohydrates
Carbohydrates are
• a major source of
energy from our diet.
• made from the
elements carbon,
hydrogen, and oxygen.
• also called
saccharides, which
means “sugars.”
Learning Goal Classify a monosaccharide as an aldose
or a ketose, and indicate the number of carbon atoms.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Carbohydrates

Carbohydrates, such as glucose,
• are produced by photosynthesis
in plants.
• are synthesized in plants from CO2,
H2O, and energy from the sun.
• are oxidized in living cells to
produce CO2, H2O, and energy.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Types of Carbohydrates
The types of carbohydrates are
• monosaccharides, the simplest carbohydrates;
• disaccharides, which consist of two monosaccharides; and
• polysaccharides, which contain many monosaccharides.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Monosaccharides
Monosaccharides
• contain several hydroxyl
groups attached to a chain of

three to eight carbon atoms.
• that contain an aldehyde
group are classified as
aldoses.
• that contain a ketone group
are classified as ketoses.
• have hydroxyl groups on all
carbons except the carbonyl
carbon.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Types of Monosaccharides
Monosaccharides are also classified by the number
of carbon atoms present.
triose (three C atoms)
tetrose (four C atoms)
pentose (five C atoms) hexose (six C atoms)

An aldopentose is a five-carbon saccharide with an
aldehyde group.
A ketohexose is a six-carbon saccharide with a
ketone group.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Types of Monosaccharides

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Study Check
Identify each as aldo or keto and as tetrose,
pentose, or hexose.
A.
B.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Solution
Identify each as aldo or keto and as tetrose,
pentose, or hexose.
A. aldohexose B. ketopentose

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


15.2 Fischer Projections of
Monosaccharides
Glucose, galactose, and fructose are the most important
monosaccharides.

Learning Goal Identify and draw the D or L configurations of
the Fischer projections for common monosaccharides.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Fischer Projections
A Fischer projection, used to represent carbohydrates,
• places the aldehyde group (most oxidized) at the top.
• shows the — H and — OH groups on the horizontal
intersecting line.
• places the achiral — CH2OH group at the bottom.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


D and L Notations
In a Fischer projection, the — OH group on the
• chiral carbon farthest from the carbonyl group determines
an L or D isomer.
• left is assigned the letter L.
• right is assigned the letter D.

Core Chemistry Skill Identifying D- and L-Fischer
Projections
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


D and L Isomers: Monosaccharides

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Important Monosaccharides

D-Glucose, D-galactose, and D-fructose are the most
important monosaccharides. They are all hexoses with the
molecular formula C6H12O6 and are isomers of each other.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Monosaccharides: D-Glucose
D-Glucose
• is the most common hexose.
• is found in fruits, vegetables, corn syrup, and honey.
• is also known as dextrose and blood sugar in the body.
• is a building block of the disaccharides sucrose and lactose
and of polysaccharides such as cellulose and glycogen.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Monosaccharides: D-Galactose
D-galactose, an aldohexose with the formula
C6H12O6,
• is obtained from the disaccharide lactose,
found in milk.
• is important in the cellular membranes of the

brain and nervous system.
In a condition called galactosemia,
• the enzyme needed to convert D-galactose to
D-glucose is missing.
• galactose accumulates in the blood and tissue,
which can lead to cataracts, mental
retardation, failure to thrive, and liver disease.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Monosaccharides: D-Fructose
D-Fructose
• is a ketohexose with the formula C6H12O6.
• is the sweetest of the carbohydrates, twice as sweet as
sucrose (table sugar).
• is obtained as one of the hydrolysis products of sucrose.
High-fructose corn syrup (HFCS)
is a sweetener that is produced by
using an enzyme to break down
sucrose to glucose and fructose.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Guide to Identifying D- or LMonosaccharides

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Study Check
Identify the following structure of a monosaccharide as D- or Lribulose.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Solution
Identify the following structure of a monosaccharide as D- or Lribulose.
ANALYZE
THE
PROBLEM

Given
ribulose

Need
identify as D­ or L­ 
Fischer projection

STEP 1 Number the carbon chain starting
at the top of the Fischer projection.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Study Check
Identify the following structure of a monosaccharide as D- or Lribulose.
STEP 2 Locate the chiral carbon farthest
from the top of the Fischer
projection.

STEP 3 Identify the position of the — OH group as D- or L-.
The — OH group is drawn on the right of carbon 4,
making it D-ribulose.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chemistry Link to Health:
Hyperglycemia and Hypoglycemia
In the body,
• glucose has a normal blood level of 70–90 mg/dL.
• a glucose tolerance test measures blood glucose for several
hours after ingesting glucose.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.