types of carbohydrates section 17.1. four types of carbohydrates monosaccharides contain a single...
TRANSCRIPT
Types of Carbohydrates
Section 17.1
Four Types of Carbohydrates
MonosaccharidesContain a single sugar unit Examples: glucose and fructose
DisaccharidesContain two monosaccharides units joined
through bridging oxygen atoms AKA glycosidic bond
Examples: sucrose and lactose
Four Types, continued
OligosaccharidesThree to ten monosaccharide units joined by
glycosidic bonds
PolysaccharidesLong, often highly branched, chains of
monosaccharidesExamples: starch, glycogen, and cellulose
Monosaccharides
Composed of carbon, hydrogen and oxygen
Most follow the general formula (CH2O)n
All names end in –oseTwo types
Ketose – monosaccharide that contains a ketone carbonyl group
Aldose – monosaccharide that contains an aldehyde carbonyl group
Ketose OR Aldose?
CH
C OHH
C OHH
C OHH
C OHH
CH2OH
O
CH
C OHH
C HHO
C OHH
C OHH
CH2OH
O
CH2OH
C
C HHO
C OHH
C OHH
CH2OH
O
CH2OH
C
C HHO
C OHH
C OHH
CH2OH
O
Ketose OR Aldose
CH
C OHH
C OHH
C OHH
C OHH
CH2OH
O
CH
C OHH
C HHO
C OHH
C OHH
CH2OH
O
CH2OH
C
C HHO
C OHH
C OHH
CH2OH
O
CH2OH
C
C HHO
C OHH
C OHH
CH2OH
O
Another system – number of carbons
Another system of nomenclature tells us the number of carbon atoms in the main skeleton.
3 carbon triose4 carbon tetrose5 carbon pentose6 carbon hexoseEtc.
Triose, tetrose, pentose, etc?
CH
C OHH
CH2OH
O CH
C OHH
C OHH
C OHH
CH2OH
OCH
C OHH
C HHO
C OHH
C OHH
CH2OH
O
Answers
CH
C OHH
CH2OH
O CH
C OHH
C OHH
C OHH
CH2OH
OCH
C OHH
C HHO
C OHH
C OHH
CH2OH
O
Triose Pentose Hexose
Combining the two systems
CH
C OHH
CH2OH
OCH
C OHH
C HHO
C OHH
C OHH
CH2OH
OCH2OH
C
C HHO
C OHH
C OHH
CH2OH
O
AldoseTrioseAldotrioseD-Glyceraldehyde
AldoseHexoseAldohexoseD-Glucose
KetoseHexoseKetohexoseD-Fructose
Stereochemistry:different spatial arrangements of atoms
Enantiomers
2 stereoisomers
that are nonsuperimposable mirror images of
one another
Chiral molecules
Molecules that exist as enantiomers (they have a right & left
version)
Chiral carbon
a carbon that has 4 different groups
attached to it
Chiral Objects
Chiral compounds have the same number of atoms arranged differently in space.
A chiral carbon atom has four different groups attached.
Mirror ImagesThe 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?
Important in biochemistry because our
biochemical processes will recognize &
act on only ONE of the chiral compounds.
The other compound is foreign to us.
Chiral or NOT?
Determine if there is a chiral carbon in each compound.
A B
C
Cl
CH3
CH2CH3
H C
Cl
CH3
H
H
Solution
A Yes, 4 different B No, the
groups are attached 2 H atoms
to the second C atom are identical
C
Cl
CH3
CH2CH3
H C
Cl
CH3
H
H
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.
D notation
C
C
CH2OH
OHH
OHH
CO
H
Right = D
Glucose
C
C
CH2OH
H OHC
OHH C
HHO
H OH
C OH
D-Glucose
D or L?
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
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
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.
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
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.
CH
OHH
HHO
OHH
OHH
CH2OH
O
O
CH2OH
HH
OHOH
H
H
OH
H
OH
O
CH2OH
HH
OHOH
H
H
OH
OH
H
D-glucose
α-D-glucose
β-D-glucose
1
2
3
4
5
6
1
1
2
2
3
3
4
4
5
5
6
6
Steps for drawingHaworth Structures for D-Glucose
1. Break the double bond2. Move the H from the –OH group on C5 to
the O on C1
3. Connect the ring structure by bonding the O on C5 directly to C1
4. Write –OH groups on the right (C2, C4) down
5. Write –OH groups on the left (C3) up6. The new –OH on C1 has two possibilites:
down for form, up for form
α-D-glucose
C
C OHH
C HHO
C OHH
C HH2CHO
H OH
O
O
CH2OH
HH
OHOH
H
H
OH
H
OH
β-D-glucose
C
C OHH
C HHO
C OHH
C HH2CHO
HO H
O
O
CH2OH
HH
OHOH
H
H
OH
OH
H
You Try This One!
Write the cyclic form of -D-galactose
C
C
C
C
C
CH2OH
OH
OHH
HO H
HHO
OHH
Solution -D-galactose
o
OH
OH
CH2OH
OH
OH
C
C OHH
C HOH
C HOH
C HCH2HO
H OH
O
Benedict’s reagent
Benedict’s 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.
Reducing Sugars
Reducing sugar – a sugar that can be oxidized by Benedict’s reagent
All monosaccharides and the common disaccharides (except sucrose) are reducing sugars.
Use of Benedict’s reagent
Benedict’s 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.