Types of Carbohydrates

1
Types of Carbohydrates

• Section 17.1

2
Four Types of Carbohydrates

• Monosaccharides
• Contain a single sugar unit
• Examples glucose and fructose
• Disaccharides
• Contain two monosaccharides units joined through
  bridging oxygen atoms AKA glycosidic bond
• Examples sucrose and lactose

3
Four Types, continued

• Oligosaccharides
• Three to ten monosaccharide units joined by
  glycosidic bonds
• Polysaccharides
• Long, often highly branched, chains of
  monosaccharides
• Examples starch, glycogen, and cellulose

4
Monosaccharides

• Composed of carbon, hydrogen and oxygen
• Most follow the general formula (CH2O)n
• All names end in ose
• Two types
• Ketose monosaccharide that contains a ketone
  carbonyl group
• Aldose monosaccharide that contains an aldehyde
  carbonyl group

5
Ketose OR Aldose?
6
Ketose OR Aldose
7
Another system number of carbons

• Another system of nomenclature tells us the
  number of carbon atoms in the main skeleton.
• 3 carbon triose
• 4 carbon tetrose
• 5 carbon pentose
• 6 carbon hexose
• Etc.

8
Triose, tetrose, pentose, etc?
9
Answers
Triose
Pentose
Hexose
10
Combining the two systems
Aldose Triose Aldotriose D-Glyceraldehyde
Aldose Hexose Aldohexose D-Glucose
Ketose Hexose Ketohexose D-Fructose
11
Chiral Objects

• Chiral compounds have the same number of atoms
  arranged differently in space.
• A chiral carbon atom has four different groups
  attached.

12
Mirror Images

• The three-dimensional structure of a chiral
  compound has a mirror image.
• Your hands are chiral. Try to superimpose your
  thumbs, palms, back of hands, and little fingers.
  Is it possible? Why or why not?

13
Chiral or NOT?

• Determine if there is a chiral carbon in each
  compound.
• A B

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Solution

• A Yes, 4 different B No, the
• groups are attached 2 H atoms
• to the second C atom are identical

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D and L Notation

• D,L tells to which of the two chiral isomers we
  are referring.
• If the OH group on the next to the bottom carbon
  atom points to the right, the isomer is a
  D-isomer if it points left, the isomer is L.
• The D form is usually the isomer found in nature.

16
D notation

17
Glucose
18
Homework

• Complete problems 17.3 and 17.4 on page 472
  17.5 and 17.6 on page 474-5 17.24, 17.25, and
  17.26 on page 493

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Importance of Glucose

• Most important sugar in the human body.
• Glucose is broken down in glycolysis and other
  pathways to release energy for body functions
• The concentration of glucose in the blood is
  carefully controlled by insulin and glucagon.
• Normal blood glucose levels are 100-120 mg/100mL

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Importance of Glucose

• Insulin stimulates the uptake of the excess
  glucose by most of the cells in the body.
• 1-2 hrs after eating the glucose levels return to
  normal.
• If glucose concentrations drop too low, the
  individual feels lightheaded and shaky. When
  this happens, glucagon stimulates the liver to
  release glucose in the blood.

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Diabetes / Hypoglycemia and Glucose

• Type I diabetes or diabetes mellitus caused by
  the inability to produce the hormone insulin If
  untreated, end up with high blood sugar
• Type II diabetes or adult-onset diabetes caused
  by insulin resistance (body fails to properly use
  insulin) combined with a relative insulin
  deficiency If untreated, end up with high blood
  sugar
• Hypoglycemia caused by the over excretion of
  insulin in response to a rise in blood sugar If
  untreated, end up with low blood sugar

22
Structure of glucose

• In reality, the open-chain form of glucose is
  present in very small concentrations in cells.
• In most cases, the cyclic intramolecular
  hemiacetal is formed.
• The hydroxyl group on C-5 reacts with the
  aldehyde group to form a hemiacetal.
• Two isomers are formed because a new chiral
  carbon is created.

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6
a-D-glucose
5
1
1
4
2
6
2
3
3
5
4
1
4
5
2
6
3
D-glucose
ß-D-glucose
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Haworth Structure for D-Glucose

• Write OH groups on the right (C2, C4) down
• Write OH groups on the left (C3) up
• The new OH on C1 has two possibilites down for
  ? form, up for ? form

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a-D-glucose
O
26
ß-D-glucose
O
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You Try This One!

• Write the cyclic form of ?-D-galactose

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Solution ?-D-galactose
O
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Benedicts reagent

• Benedicts reagent a basic buffer solution that
  contains Cu2 ions
• It readily oxidizes the aldehyde group of aldoses
  to form a brick red Cu2O precipitate.
• It will also oxidize ketoses because of the OH
  group on the carbon next to the carbonyl group.

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Reducing Sugars

• Reducing sugar a sugar that can be oxidized by
  Benedicts reagent
• All monosaccharides and the common disaccharides
  (except sucrose) are reducing sugars.

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Use of Benedicts reagent

• Benedicts reagent was commonly used to
  qualitatively monitor excess glucose in the urine
  by diabetics to insure proper dosage of insulin.
  
• These have been replaced by blood glucose tests
  that are more accurate.