A Getting-It-On Review and Self-Test
Carbohydrates
Carbohydrates, one of the three principal classes of foods, contain only
three elements: (1)
, (2)
, and (3)
. The name
carbohydrate is derived from the French hydrates de carbone because the
empirical formula in many cases is (4)
. Carbohydrates are
actually aldehydes or ketones that contain many (5)
groups.
The simplest carbohydrates are glyceraldehyde and dihydroxy acetone.
A classification system for carbohydrates is based on the number of
units linked together. If there is only one unit, the carbohydrate is
termed a (6)
. Two units linked together are a (7)
, such as sucrose, while long chain carbohydrates, such as glycogen and
cellulose, are (8)
. The most common monosaccharide, (9)
, has (10)
asymmetric carbon atoms. The number of isomers
related to glucose is (11)
. All of these have been synthesized,
but only D–glucose and D–galactose are of biological importance. Another
common hexose, fructose, is a (12)
, and when linked to glucose,
it forms the disaccharide (13)
. Other disaccharides are
(14)
and lactose which is known also as (15)
. All
monosaccharides and most disaccharides are reducing sugars capable of
reducing silver ions and copper ions. The only common sugar that is not
a reducing sugar is the disaccharide (16)
.
The hemiacetal structure of carbohydrates involves an alcohol linkage
and a(n) (17)
linkage on the same carbon atom. Acetal
structures have (18)
ether linkages to the same carbon. The
hemiacetal or cylic form is unstable and hydrates easily to the open form,
which can reform to the other diasteromer. The symbols used for the two
forms are alpha () and beta (19)
. Each of the diasteromers
rotates polarized light and in solution there is an equilibrium between
the forms. Diasteromers that differ in spatial arrangement only on C–1
carbon are called (20)
. The switching back and forth from  to 
forms is called (21)
and occurs in hemiacetals but not
(22)
. Glycosides such as cellulose and starch are only ether
linkages and are therefore (23)
structures and (24)
exhibit mutarotation. Lactose and maltose undergo mutarotation,
which means at least one of their monosaccharides has a (25)
ring structure. Sucrose does not undergo mutarotation, which means
only (26)
or (27)
linkages.
2
28.
For each of the following carbohydrate molecules, pick out all of
the correct descriptive terms from the list below that apply to the
particular molecule.
descriptive terms
triose
tetrose
pentose
hexose
aldose
ketose
a.
reducing sugar
non-reducing sugar
D configuration
L configuration
b.
c.
H
O
C
CH2OH
H
H
O
C
H
C
OH
H
CH2OH
d.
H
C
OH
HO
C
H
C
OH
C
O
H
C
OH
C
OH
H
C
OH
CH2OH
CH2OH
e.
f.
CH2OH
H
C
H
O
C
O
C
O
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
C
OH
H
C
OH
H
C
OH
HO
C
H
H
C
OH
CH2OH
CH2OH
g.
h.
H
C
CH2OH
HO
O
H
C
OH
C
O
HO
C
H
C
H
HO
C
H
CH2OH
CH2OH
CH2OH
3
29.
Examine the carbohydrate formulas below and then answer the
questions that follow.
a.
b.
c.
H
OH
C
H
C
OH
HO
C
H
H
C
OH
H
C
CH2O H
O
HO
CH2OH
d.
O
H
OH
OH
H H
H
OH
e.
O
H
C
HOCH2
O
HH
OH
HO
OH
(1)
(2)
(3)
(4)
(5)
30.
CH2OH
H
C
H
H
C
OH
H
C
OH
CH2OH
H
Identify the pyranose and furanose ring structures.
Identify the Fisher projection, “tree”, and Haworth formulas.
Identify the hemiacetal forms.
How many carbons are there in the “tree” formula
carbohydrate?
Identify (a) and (e) as either D and/or L.
Match the disaccharide in the left with their two constituent
monsaccharides from the list on the right.
disaccharides
(1)
(2)
(3)
sucrose
lactose
maltose
monosaccharides
glucose
fructose
galactose
4
31.
Match a possible source from the right with the sugar listed on the
left.
sugar
(1)
(2)
(3)
(4)
(5)
(6)
32.
33.
source
glucose
galactose
fructose
sucrose
lactose
maltose
source
fruit juice
sugar beets
starch
sucrose
lactose
pectin
honey
milk
sugar cane
sprouting grain
agave
Match the polysaccharide with the correct descriptive statement.
(1)
starch
a.
(2)
cellulose
b.
(3)
glycogen
c.
(4)
inulin
d.
glucose units, -1,4 linkage, highly
branched
fructose units, 1,2-linkage
glucose units, -1,4 linkage,
moderately branched
glucose units, -1,4 linkage
Complete the following reactions.
a.
H
R
C
O
+ 2 Cu+2
+
What is the visual evidence of positive test
b.
H
O
C
HO
H
C
C
H
OH
CH2OH
Br2
H2O
+ 3 H2O
5
c.
H
O
C
HO
C
H
H
C
OH
HNO3
CH2OH
d.
H
O
C
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H2
Pt
CH2OH
ANSWERS
1. carbon
2. oxygen
3. hydrogen
4. (CH2O)n
5. hydroxy
6. monosaccharide
7. disaccharide
8. polysaccharides
9. glucose
10. four
11. Sixteen
12. ketose
13. sucrose
14. maltose
15. milk sugar
16. sucrose
17. ether
18. two
19. 
20. Anomers
21. mutarotation
22. acetals
23. acetal
24. do not
25. hemiacetal
26. acetal
27. ether
6
28.
a.
b.
c.
d.
e.
f.
g.
h.
triose, aldose, reducing, D
pentose, ketose, nonreducing, D
hexose, aldose, reducing, D
hexose, ketose, reducing, D
pentose, aldose, reducing, L
pentose, aldose, reducing, D
tetrose, ketose, reducing, L
pentose, aldose, reducing, L
29.
(1)
(2)
(3)
(4)
(5)
b and c are pyranose, d is furanose
Fischer projections are b and e, tree formula is a, and
Haworth formulas are c and d
Hemiacetal forms are b, c, d
Tree formulas has six carbons, a hexose
a is “D” and e is “D”
30.
(1)
(2)
(3)
sucrose – glucose & fructose
lactose – glucose & galactose
maltose – two glucose units
31.
(1)
(2)
(3)
(4)
(5)
(6)
glucose – starch & sucrose
galactose – lactose & pectin
fructose – honey, sucrose, fruit juice, agave
sucrose – sugar cane, sugar beets
lactose – milk
maltose – sprouting grain
32.
(1)
(2)
(3)
(4)
starch – c
cellulose – d
glycogen – a
inulin – b
33.
a.
R
C
HO
b.
_
O
O
+
O
C
Cu2O
The Cu2O will be a brick-red precipitate
HO
C
H
H
C
OH
CH2OH
c.
HO
O
C
d.
CH2OH
HO
C
H
H
C
OH
COOH
H
C
OH
HO
C
H
H
C
OH
H
C
OH
CH2OH