Carbohydrates

1
Carbohydrates

• Classification
• Monosaccharides
• Chiral Carbon Atoms
• Cyclic Structures

2
Biochemistry

• Biochemistry study of the chemical substances
  in living organisms and the interactions that
  these substances have on each other
• Biochemical substance chemical substances in
  living organisms

3
Carbohydrates

• Carbohydrate- a polyhydroxy aldehyde, a
  polyhydroxy ketone, or a compound that produces
  one of these compounds after hydrolysis
• The most abundant organic compounds in plants

4
Carbohydrates

• Major source of energy from our diet
• Are a part of DNA and RNA
• Produced by photosynthesis in plants
• Are also called saccharides

5
Types of Carbohydrates

• Monosaccharides to have a single polyhydroxy
  aldehyde or polyhydroxy ketone unit
• 1 monosacchride unit - General formula
  CnH2nOnbut not all compounds in the class fit
  the formula
• Disaccharides
• Contain 2 monosacchride units
• Oligosaccharides
• Contain multiple ( 2-100s) monosaccharide units
• Polysaccharides
• Contain 100s to 1000s of monosaccharide units

6
Monosaccharides

• Monosaccharides found in nature have 37 carbons
• Three Carbons Triose
• Four Carbons Tetrose
• Five Carbons Pentose
• Six Carbons Hexose
• Seven Carbons Heptose

7
Monosaccharides

• Monosaccharides are classified based on the type
  of carbonyl that is present
• Aldoses are monosaccharides with an aldehyde
  group and many hydroxyl (-OH) groups.
• Ketoses are monosaccharides with a ketone group
  and many hydroxyl (-OH) groups.
• Are often classified by both their number of
  carbon atoms and their functional group
• Also called sugars

8
Carbohydrate Nomenclature

• Aldoses
• Contain aldehyde
• Name aldo-of carbons-oses
• (e.g., aldohexoses for a 6 C aldehyde
  monosaccharide)
• Ketoses
• Contain ketones
• Name keto- of carbons-oses
• (e.g., ketohexose for a 6 C ketone
  monosaccharide)

9
Aldoses
O
HOCH2CHCH OH
C
H
O
C
HOH
same as
C
H
OH
2
glyceraldehyde (an aldotriose)
10
Ketoses
C
H
O
HOCH2CCH2OH
2OH
same as
C
O
C
H
OH
2
Dihydroxyacetone (a ketotriose)
11
Learning Check

• Identify each as (aldo or keto) tetrose,
  pentose or hexose

12
Solution

• A B
• aldohexose ketopentose

13
Chiral Objects

• Chiral compounds have a chiral center
• Chiral center atom in a molecule that has 4
  different groups bonded to it
• Chiral molecule molecule whose mirror images
  are not superimposable
• Achiral molecule molecule whose mirror images
  are superimposable
• A molecule can have multiple chiral centers

14
Learning Check C2

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

C
l
C
C
H
H
3
C
H
C
H
2
3
15
Solution C2

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

16
Mirror Images

• The three-dimensional structure of a chiral
  compound has a mirror image.
• Your hands are chiral and are nonsuperimposable
  mirror images
• Nonsuperimposable mirror images have a
  handedness
• Handedness is either left or right

17
Fischer Projections

• 2-D representation showing the spatial
  arrangement of groups around a chiral center
• The chiral center is the intersection of vertical
  and horizontal lines
• The carbon chain is on the vertical line with the
  carbonyl near the top
• Leads to the possibility of 2 drawings
• a left and right handed form

C
H
O
C
HOH
C
H
OH
2
18
Stereoisomers

• The left and right handed forms of a chiral
  molecule are isomers, specifically stereoisomers,
  that exist in a D-form and an L-form
• Stereoisomers isomers that have the same
  molecular and structural formulas but different
  spatial orientations
• 2 Types - enantiomers or diastereomers

19
Stereoisomers

• Enantiomers stereoisomers whose molecules are
  nonsuperimposable mirror images
• Includes the left and right handed forms of a
  chiral molecule
• Diastereomers stereoisomers whose molecules are
  not mirror images of each other
• Includes cis-trans isomers and molecules with
  multiple chiral centers

20
D and L Notation

• D and L describes which of the two chiral isomers
  we are referring to
• Is determined by looking at the chiral carbon
  furthest away from the carbonyl
• If the OH group on the bottom chiral carbon
  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
  for sugars

21
D notation

O
C
H
C
O
H
H
C
O
H
H
C
H
O
H
2
R
i
g
h
t



D
22
Glucose
H
C
O
C
H
O
H
C
H
H
O
O
H
H
C
H
O
H
C
C
H
O
H
2
D
-
G
l
u
c
o
s
e
23
Fructose
C
H
OH
2
C
O
C
H
H
O
O
H
H
C
H
O
H
C
C
H
O
H
2
D
-
F
r
u
c
t
o
s
e
24
Galactose
O
H
C
C
O
H
H
C
H
O
H
C
H
H
O
C
O
H
H
C
H
O
H
2

• D-galactose

25
Examples of Stereoisomers
enantiomers
O
O
O
O
OH
HO
HO
OH
HO
HO
HO
OH
OH
OH
HO
OH
HO
OH
OH
OH
CH
OH
CH
OH
CH
CH
OH
OH
2
2
2
2
diastereomers
diastereomers
D-Glucose
D-mannose
D-Talose
L-Talose
26
ACETALS AND HEMIACETALS
aldehyde
hemiacetal
acetal
ketone
27
Cyclic Structures

• Monosaccharides with 5-6 carbon atoms form cyclic
  structures
• The -OH on C-5 reacts with the aldehyde group or
  ketone group to form a stable hemiacetal
• All OH on the right in a Fisher projection are
  below the ring and those on the left are above
  the ring in cyclic structures
• The ring formation results in a chiral C at C-1
  so 2 stereoisomers are possible (a (alpha) and ß
  (beta))

Pyranose ring
Furanose ring
28
Cyclic Structures

• The cyclic structures that result from the
  hemiacetal formation are called Haworth
  Projections
• Haworth Projection a 2-D drawing the specifies
  the 3-D structure of a cyclic form of a
  monosaccharide
• D and L in Haworth Projections are determined by
  the direction of the last CH2OH group in the
  molecule
• D This group is above the ring
• L This group is below the ring

29
HAWORTH PROJECTIONS
It is convenient to view the cyclic sugars
(glucopyranoses) as a Haworth Projection, where
the ring is flattened.
Standard Position
HAWORTH PROJECTION
upper-right back
This orientation is always used for a Haworth
Projection
a-D-()-glucopyranose
30
AN OPEN CHAIN CAN CONVERT TO EITHER ANOMER
FISCHER
HAWORTH
a-ANOMER
OPEN CHAIN
b-ANOMER
You cant tell which anomer will result
(predominate) when you look at the Fischer
Projection.
That information is not contained in Fischer
Projection.
31
Sugar Anomers

• The formation of a cyclic hemiacetal in sugars
  results in an chiral carbon atom.
• Isomers that differ only in their configuration
  about the new chiral carbon are called anomers
• The newly formed chiral carbon is called
  anomeric carbon and can exist in two forms
• a-anomer has the hydroxyl group on the opposite
  side (trans) of the ring as the CH2OH used to
  denote D vs. L
• ß-anomer has the hydroxyl group on the same side
  (cis) of the ring as the CH2OH used to denote D
  vs. L

32
HAWORTH PROJECTIONS
HERE ARE SOME CONVENTIONS YOU MUST LEARN
1) The ring is always oriented with the oxygen
in the upper right-hand back corner.
D
2) The -CH2OH group is placed UP for
a D-sugar and DOWN for an L-sugar.
L
3) a-Sugars have the -CH2OH group and the
anomeric hydroxyl group trans.
a
b
4) b-Sugars have the -CH2OH group and the
anomeric hydroxyl group cis.
33
SOME HAWORTH PROJECTIONS
D-SUGARS
b-D
ANOMERS
a-D
BOTH OF THESE ARE D-GLUCOSE
34
SOME HAWORTH PROJECTIONS
L-SUGARS
a-L
ANOMERS
b-L
BOTH OF THESE ARE L-GLUCOSE
35
CONVERTING TO HAWORTH PROJECTIONS
D-()-glucose
-CH2OH up D
D O W N
U P
1
6
BOTH ANOMERS OF A D-SUGAR (D-glucose)
2
5
3
1
4
4
2
3
5
6
HAWORTH PROJECTIONS
FISCHER PROJECTION
36
HAWORTH PROJECTIONS OF L-SUGARS
L-()-glucose
D O W N
U P
BOTH ANOMERS OF A L-SUGAR (L-glucose)
on left L
HAWORTH PROJECTIONS
FISCHER PROJECTION
37
CONVERTING FISCHER TO HAWORTH PROJECTIONS
CAUTION !
Students often get the erroneous impression that
all the Haworth rules are reversed for L-sugars
- this is not the case!
The only difference when converting D- and L-
sugars is
These rules are the same for both D- and
L- sugars
LEFT UP RIGHT DOWN
b cis a trans
D-sugars -CH2OH UP
L-sugars -CH2OH DOWN
38
FRUCTOSE
standard position
cis b
up D
1
..

anomeric carbon
2
6
3
2
5
..
4
3
4
1
..
5
6
b-D-(-)-Fructofuranose
D-(-)-Fructose
39
Disaccharides and Polysaccharides
40
Disaccharides

• Simplest oligosaccharides
• Contain two monosaccharides linked by a
  glycosidic bond
• Glycosidic linkage or bond the bond in a
  disaccharide the occurs then the OH of one
  monosaccharide reacts with the OH of a second
  monosaccharide
• The newly formed bond results in an ether
  functional group

41
Important Disaccharides

• Maltose Glucose Glucose
• - malt sugar
• Lactose Glucose Galactose
• - milk sugar
• Sucrose Glucose Fructose
• - table sugar

42
Sucrose
C
H
O
H
2
o
O
H
a,ß-1,2- glycosidic bond
O
H
O
H
O
C
H
O
H
2
O
O
H
C
H
O
H
2
O
H
43
Lactose
C
H
O
H
2

• ? -1,4-glycosidic bond

H
H
O
C
H
O
H
2
H
H
O
H
O
O
H
O
H
O
H
O
H
O
H
H
H
H
O
H
?
H
44
Maltose
?

• ? -1,4-glycosidic bond

C
H
O
H
C
H
O
H
2
2
H
H
O
O
H
O
H
H
H
H
H
O
H
O
H
O
O
H
H
O
H
O
H
H
H
45
Polysaccharides

• Polysaccharide a polymer of many
  monosaccharides bonded together by glycosidic
  linkages
• Also known as glycans
• Polysaccharides differ in the 1) identity of the
  monosaccharides in the polymer, 2) length of the
  polymer, 3) type of glycosidic bond, 4) amount of
  branching in the polymer
• Are not sweet and have little solubility in water

46
Types of Polysaccharides

• Polysaccharides are used for storage and
  structural purposes, as well as for cell
  recognition
• Storage polysaccharide a polysaccharide that is
  used as storage and is ultimately used as an
  energy source
• Structural polysaccharide a polysaccharide that
  serves as a structural element in the cell walls
  of plants and exoskeletons of animals
• Cell Recognition linking polysaccharides to
  lipids or proteins for various cellular functions

47
Polysaccharides

• Storage
• Starch
• Glycogen
• Structural
• Cellulose
• Chitin

48
Polysaccharides

• Polymers of a-D-Glucose

C
H
O
H
2
H
O
O
H
H
H
O
H
O
H
H
O
H
H
49
Amylose

• Glucose polymer with a-1,4 bonds of in a straight
  chain
• a-1,4 bonds

C
H
O
H
C
H
O
H
2
C
H
O
H
2
C
H
O
H
2
2
H
H
H
H
O
O
H
H
H
O
H
O
H
H
H
H
H
H
H
H
O
H
O
H
O
H
O
H
O
O
O
O
O
O
H
O
H
H
H
O
H
H
O
H
H

50
Amylopectin

• Glucose Polymer with a-1,4 and a-1,6 bond
  branches
• a-1,6 bond
• a-1,4 bonds

O
Note that the ends of the lines should actually
be Hs
51
Cellulose

• Glucose Polymer with ß-1,4 bonds
• ß-1,4 bonds

C
H
O
H
2
O
O
O
H
C
H
O
H
2
O
O
O
H
O
H
C
H
O
H
2
O
O
O
H
O
H
O
O
H
Note that the ends of the lines should actually
be Hs