Carbohydrate chemistry Flashcards
1
Q
What is the general formula for disaccharides?
A
(C12H22O11)
2
Q
What is the general formula for polysaccharides?
A
(C6H10O5)n
3
Q
What is the general formula for monosaccharides?
A
(CH2O)n
4
Q
What do carbohydrates consist of?
A
An aldehyde , OR a ketone group with 2 or more hydroxyl groups
5
Q
What type of sugar is glucose
A
An aldohexose sugar
6
Q
Ribulose is an example of a…
A
Keto - pentose sugar
7
Q
Hemiketal formation is a reaction between :
A
A ketone and alcohol
8
Q
Hemiacetal formation is a reaction between:
A
An aldehyde and alcohol
9
Q
What type of ring does fructose form during hemiketal formation?
A
A furanose ring
10
Q
Name the epimers of glucose.
A
Mannose and galactose
11
Q
How many carbons are present IN a pyranose ring?
A
5
12
Q
List the storage polysaccharides.
A
Starch[Plant polysaccharide]
Glycogen
13
Q
List the structural polysaccharides.
A
Cellulose[plant polysaccharide]
Chitin[animal polysaccharide]
14
Q
List the heteropolysaccharides.
A
Peptidoglycans , glycoproteins , glycolipids , glycosaminoglycans , Proteo - glycans
15
Q
what are the major constituents of starch?
A
amylopectin(2%) and amylose(98%)
16
Q
what is found in glycosaminoglycans?
A
D-glucoronic acid
17
Q
What are the properties of amylopectin?
A
- Amylopectin is approximately 2% of starch
- amylopectin has alpha (1-6) glycosidic linkage at branch points.
- Amylopectin is a highly branched polymer of glucose
- Branch points are located approximately at every 24
- 30 glucose units
- The helix formation interrupts colour formation with iodine
18
Q
Chitin is a homo - polysaccharide of :
A
N-Acetyl-D-Glucosamine residues
19
Q
What are the N-Acetyl-D-Glucosamine residues linked by?
A
Beta(1,4) linkages
20
Q
Cellulose forms a stable fibrous network linked by:
A
Hydrogen bonds
21
Q
Which glycosidic bonds are present in amylopectin?
A
alpha (1 - 6) and alpha (1 - 4) glycosidic linkages
22
Q
Concentration of glycogen in the liver and muscle is usually ……………% and …………….% of their total weights, respectively.
A
Liver - 10% ; muscle - 2%
23
Q
What is the statement that is most appropriate for reducing sugars?
A
Reducing sugars may have free aldehyde or keto group or free anomeric carbon.
24
Q
The disease ‘Multiple sclerosis’ is called so because……………….
A
multiple plaques form in the myelin sheath of neuronal cells
25
Carbohydrates are essential components of all living organisms such as-
```
Humans
Plants
Animals
Bacteria
Viruses
```
26
What are carbohydrates defined as?
Carbohydrates are defined chemically as aldehyde (-CHO)
or ketone (=C=O) derivatives of polyhydric (more than one –
OH groups) alcohols such as – Glyceraldehyde, Dihydroxy
acetone, Glucose, Fructose etc.
27
Chemistry of carbohydrates :
Carbohydrates have one aldehyde (-CHO) or ketone (=C=O) group
with two or more hydroxyl (-OH) groups in their structures.
28
Carbohydrates are classified into 4 major classes based on the number of monomeric units present. Name the 4 major classes
1. Monosaccharides
2. Disaccharides
3. Oligosaccharides
4. Polysaccharides
29
What are monosaccharides?
Monosaccharides are the basic unit of carbohydrates. They can't be hydrolysed into a simpler form of carbohydrates as they are already in the simplest form
30
Every individual monomeric unit of carbohydrate is called
Monosaccharide - glucose , fructose , galactose , ribose[in RNA] , deoxyribose[in DNA] , etc.
31
Monosaccharides can be sub-divided into several classes
depending on the number of carbon atoms present in their
structures such as -
i. Trioses – 3 carbon monosaccharides
ii. Tetroses – 4 carbon monosaccharides
iii. Pentoses – 5 carbon monosaccharides
iv. Hexoses – 6 carbon monosaccharides
v. Heptoses – 7 carbon monosaccharides
32
Define the term 'disaccharides'
Disaccharides are carbohydrates that can be hydrolysed into 2 molecules of the same or different monosaccharides
33
Sucrose is the most ...
Abundant disaccharide
34
Where is sucrose synthesized?
Sucrose is synthesized mainly in plants such as - sugarcane , sugar beet , etc.
35
Lactose is a major disaccharide that comes from ...
milk
36
What is released during the hydrolysis of starch?
Maltose is released from the hydrolysis of starch, a plant
| polysaccharide.
37
What is cellobiose?
Cellobiose is the repeating disaccharide in cellulose
38
Where is cellulose found?
Cellulose is found only in the plant world.
39
What is the difference between maltose and cellobiose?
The difference between maltose and cellobiose is only in
the glycosidic link
maltose - alpha[1,4] glycosidic bond
cellobiose - beta[1,4] glycosidic bond
40
What is the general formula of disaccharides and where does it come from?
The general formula of disaccharides is: C12 H22O11 which
| comes from C12H24O12 – H2O (dehydration)
41
maltose hydrolysis products :
D-glucose + D-glucose
42
sucrose hydrolysis products :
D-glucose + D-fructose
43
lactose hydrolysis products :
D-glucose + D-galactose
44
cellobiose hydrolysis products:
D-glucose + D-glucose
45
What are oligosaccharides?
Oligosaccharides are carbohydrates that can be hydrolyzed into 3 – 20 of
the same or different monosaccharide units such as - Fructooligosaccharide (FOS),
Galactooloigosaccharides (GOS).
46
what are polysaccharides?
Polysaccharides are carbohydrates that can be hydrolyzed into more than
20 monosaccharides units such
as – starch, cellulose (plant polysaccharides), glycogen,
chitin (animal polysaccharide).
47
What are isomers?
Isomers are molecules that consist of the same number and kinds of
atoms but differ in their structure or spatial configurations
48
Isomers of carbohydrates are classified into two
| different classes, such as -
i. Structural isomers
| ii. Optical isomers or stereo-isomers
49
What are structural isomers?
Structural isomers are compounds that have the same molecular formula but
differ in structural formula
50
The structural isomerism of carbohydrates can be shown
| into two different ways, such as -
a) Aldose-Ketose isomerism
| b) Pyranose-Furanose Ring isomerism
51
Briefly describe aldose - ketose isomerism.
When one aldose sugar and one ketose sugar are same in
molecular formula but differ in structural formula that is
called aldose-ketose isomerism.
52
Briefly describe pyranose - furanose isomerism.
When a PYRANOSE RING and a FURANOSE RING of
carbohydrates are same in molecular formula but differ in
structural formula that is called pyranose-furanose
isomerism.
53
The pyranose and furanose are the ring structure of
ALDOSE and KETOSE sugar, respectively
54
Glucose and fructose are usually in..
straight chain form
55
The predominant form of glucose and fructose in solution is ...
Is not open - chain structures
56
What did the English chemist WN Haworth show?
The English chemist WN Haworth showed that the open
chain forms of ALDOHEXOSE and KETOHEXOSE i.e. glucose
and fructose respectively and some other sugars can cyclize
into rings.
57
How does glucose , fructose and some other sugars react?
they react internally to form cyclic
| HEMIACETALs or HEMIKETALS.
58
What are the ring structures of aldose and ketose sugars called?
The ring structures of aldose and ketose sugars are
| also called HAWORTH PROJECTION.
59
What is hemiacetal formation?
Hemiacetal formation is a characteristics reaction between
| aldehyde and alcohols
60
Briefly describe pyranose ring formation[hemiacetal formation].
The aldehyde group (-CHO) at C1 and hydroxyl (-OH) at C5
of a glucose molecule combined together via hemiacetal
formation to synthesize a PYRANOSE ring
61
What is hemiketal formation?
Hemiketal formation is a characteristics reaction between
| ketone and alcohols
62
Briefly describe Furanose ring formation[hemiketal formation].
The ketone group (=CO) at C2 and hydroxyl (-OH) at C5 of
a fructose molecule combined together via hemiketal
formation to synthesize a FURANOSE ring
63
What is an optical or stereo- isomer?
Optical or stereo - isomers are compounds that have the same structural formula but
differ in spatial configuration
64
What causes stereo-isomer formation to occur?
Stereo-isomer formation occurs due to the presence of
| asymmetric/ chiral center/ chiral carbon atoms.
65
What is an asymmetric carbon?
An asymmetric carbon is a carbon atom to which 4 different atoms or groups of
atoms are attached
66
All monosaccharides have one or more asymmetric or chiral carbon atoms except
dihydroxyacetone
67
How many asymmetric/chiral carbon atoms does D- or L- glyceraldehyde have?
D- or L-glyceraldehyde each of them have
| one asymmetric/ chiral carbon atom.
68
What are enantiomers?
Enantiomers - When two optical or stereo-isomers are mirror images to
each other. For example- D- and L-glyceraldehyes or D- and L-Alanine
are enantiomers
69
What are epimers?
Epimers are sugar molecules that differ in configuration at only 1 of several chiral centers. epimers are Isomers that differ as a result of variation in configuration
of the H or OH on a single C atom (2, 3 or 4) of a hexose
molecule
70
What are the most important epimers of glucose[biologically]?
Biologically the most important epimers of glucose are:
galactose and mannose, formed by epimerization at carbon
number 2 and 4 respectively.
71
Why are D-Mannose and D-Galactose called diastereomers?
```
D-Mannose
and D-galactose vary
at two C atoms(C2 &
C4) hence, they are
neither epimers nor
enantiomers but they
are called
DIASTEREOMERS
```
72
What is an anomer?
An anomer is one of two sugar molecules that are epimeric at the hemiacetal or hemiketal carbon atom (carbon-1 in aldoses, carbon-2 in most ketoses)
73
Which carbon from the straight chain form becomes an
| asymmetric centre in the ring form of glucose?
C1 from the straight chain form becomes an
| asymmetric centre in the ring form of glucose
74
```
Two different structures are formed based on this
asymmetric carbon (C1), For example -
```
α-D-glucose:
-OH group is below the plane of the ring
β-D-glucose:
-OH group is above the plane of the ring
75
What are the alpha and beta forms of glucose called? Which carbon is the anomeric carbon?
These α and β forms of carbohydrate
(glucose) are called anomers and C1 is
called the anomeric carbon
76
What is an anomeric carbon?
An anomeric carbon is the most oxidized carbon of a cyclized monosaccharide , the one attached to 2 oxygen atoms.
For example, C1 in the ring form of glucose is an anomeric carbon
77
What confers the optical activity on the compounds?
The presence of an asymmetric carbon confers the optical activity on the compounds
78
Why are optical isomers called enantiomers ?
Optical isomers are also mirror image to each other hence
they are ENANTIOMERS.
These compounds are seem like the left and right hand
79
Enanatiomers have similar properties e.g.
```
These compounds have similar properties e.g.
◦ Same boiling point
◦ Same melting point
◦ Same solubility and so on
but different optical activity
```
80
The enantiomers are simply named -
These two compounds are simply named as Dextrorotatory
or D and Levorotatory or L. For example- D-Alanine and L-
Alanine.
81
Briefly describe dextrorotatory or D(+)
```
Dextrorotatory or D (+):
When an optically active compound
rotates the plane of polarized light
on clockwise or right direction that
is called DEXTROROTATORY or D.
```
82
Briefly describe Levororotatory or L(-)
```
Levorotatory or L (-):
When an optically active compound
rotates the plane of polarized light
on ant-clockwise or left direction
that is called LEVOROTATORY or L.
```
83
In which direction does an optically active compound rotate the plant of polarized light?
An optically active compound rotates the plant of polarized
| light either RIGHT or LEFT direction.
84
What is specific/optical rotation?
A specific amount of angle rotates by the plane of polarized
light for a particular compound that is called its specific or
optical rotation.
85
The specific rotation is..
a standard measure degree of the
| compound which is dextrorotatory or leverotatory
86
Describe the specific rotation of dextrorotatory and Levororotatory.
Dextrorotatory compounds have positive (+ve) specific
rotation while levorotatory compounds have negative (-ve)
specific rotation.
87
what do 2 enantiomers have?
Two enantiomers have equal and opposite specific rotation.
88
What is the specific rotation of D- and L- Bromobutane?
```
D-bromobutane = +23.1 degrees Celsius
L-bromobutane = -23.1 degrees Celsius
```
89
What is the specific rotation of alpha and beta - D - glucose?
α-D(+) glucose = +112 degrees Celsius
| β-D(+)-glucose = +19 degrees Celsius
90
What happens when alpha - and beta - forms of a compound are dissolved in water?
The specific rotation of each form of the compound
gradually changes with time and approach to final
equilibrium value that is called MUTAROTATION.
91
What is mutarotation?
Mutarotation is the gradual change of optical rotations of two
compounds, which continues until equilibrium is
established, is known as MUTAROTATION
92
What is the mutarotation of α-D(+) glucose = +112 degrees Celsius[specific rotation] and
β-D(+)-glucose = +19 degrees Celsius[specific rotation] mixture?
The mutarotation of the mixture is +53 degrees Celsius.
This value is not the average of their specific rotations
[(112+19)/2 = 65.5]
93
Why is mutarotation significant?
Mutarotation is significant because the quantities of the α and β forms of a given compound in a mixture can be calculated. Compounds can also be separated by their physical and chemical properties based on their mutarotation. e.g., by crystallization.
94
What happens if α-D-glucose and β-D-glucose are dissolved
| in ethylalcohol and then allowed to crystallize?
If α-D-glucose and β-D-glucose are dissolved
| in ethylalcohol and then allowed to crystallize, only the α-D-glucose will be crystallized
95
What happens if α-D-glucose and β-D-glucose are dissolved in acetic acid
and then allowed to crystallize?
If α-D-glucose and β-D-glucose are dissolved in acetic acid
and then allowed to crystallize, only the β-D-glucose will be
crystallized
96
What are disaccharides?
Disaccharides are natural carbohydrates usually contain more than one
monosaccharide units.
97
What do monosaccharides tend to do?
Monosaccharides have a tendency to reach to hydroxyl
| compounds to form stable acetals called GLYCOSIDES.
98
How are these glycosides classified?
These glycosides are classified according to the sugars they are derived from such as -
Glucoside from glucose
Galactoside from galactose etc.
99
What is the linkage between 2 monosaccharide units called?
```
The linkage (-C-O-C-) between two monosaccharide units
is called a glycosidic or galactosidic linkage
```
100
How are disaccharides formed?
When two monosaccharide units are joined to each other by a
| glycosidic or galactosidic linkage
101
All disaccharides have the same molecular formula which is
| C12H22O11 and hence...
They are structural isomer to one
| another.
102
List the common disaccharides
Maltose
Sucrose
Lactose
Cellobiose
103
List the hydrolysed products/compositions of each disaccharide.
* Maltose = D-glucose + D-glucose
* Sucrose = D-glucose + D-fructose
* Lactose = D-glucose + D-galactose
* Cellobiose = D-glucose + D-glucose
104
What is maltose formed by?
Maltose is formed by the action of enzyme
- Diastase in plants and
- Ptyalin in animals
105
What is the hydrolysis of maltose catalysed by and what does it yield?
The hydrolysis of maltose is catalysed by the enzyme MALTASE
and yields glucose units only
106
How are the 2 α-D-glucopyranose components joined?
The TWO α-D-glucopyranose components are joined head-to-tail through C1 of one glucose molecule and C4 of second
glucose molecule.
107
What is the linkage between the glucose units of maltose?
The linkage is α-1, 4-GLUCOSIDIC linkage.
| α (1,4) glycosidic bond
108
Is maltose a reducing sugar?
Yes
109
What is lactose exclusively associated with?
Lactose is exclusively associated with animal kingdom
110
What lactose also called?
Lactose is also called MILK carbohydrate such as- in human milk:
5-8% and Cow milk: 4-6%.
111
Briefly describe the hydrolysis of lactose.
Lactose can be hydrolyzed by dilute mineral acid or by
enzyme LACTASE to yield equal concentrations of D-glucose
and D-galactose.
112
What are the monosaccharide units of lactose joined by?
The monosaccharides units of lactose are joined by a β-1, 4-
| galactosidic/glycosidic linkage.
113
What is the α-form of lactose is used to prepare?
The α-form of lactose is used to prepare INFANT FOOD and
| PENICILLIN.
114
What specific rotation does the equilibrium mixture of the α- and β-form of lactose have?
The equilibrium mixture of the α- and β-form of lactose has
| a specific rotation of +55 degrees Celsius.
115
What is cellobiose a stereoisomer of?
Cellobiose is a stereoisomer of maltose
116
What cellobiose a product of?
Cellobiose is a product of the hydrolysis of cellulose polysaccharide
117
What does cellobiose contain?
Cellobiose contains TWO glucose units, which are joined by
| β-1, 4-glycosidic bond.
118
List one similarity between maltose and cellobiose.
They are both reducing sugars that undergo mutarotation
119
What is sucrose usually obtained from?
Sucrose is usually obtained from sugarcane and sugar beet.
120
Sucrose is the most
widely used sweetening agent in the world
121
Where is sucrose synthesized?
Sucrose is synthesized in all photosynthetic plants.
122
What does sucrose consist of?
Sucrose consists of ONE molecule of α-D-glucopyranose (glucose)
and ONE molecule of β-D-fructofuranose (fructose).
123
Briefly describe the formation of a sucrose molecule.
C1 of α-D-glucose and the –OH group on C2 of β-D-fructose are linked by an α-1,2-glycosidic bond to form a
SUCROSE molecule.
124
What is the glycosidic bond of sucrose hydrolysed by?
This glycosidic bond of sucrose can be hydrolyzed by
mineral acids (e.g. H2SO4 or HCl) or by the enzyme
SUCRASE (invertase).
125
Sucrose does not show mutarotation, why?
Because of the 1,2-glycosidic bond sucrose cannot exist in
the α- or β-configuration or in the OPEN chain form.
So it does not exhibit mutarotation and exists only in one
form in the solid state or in solution.
126
Sucrose is a non-reducing sugar, why?
The reason is, the potential aldehyde (-CHO) group of
glucose and potential keto (=C=O) group of fructose are
involved in the 1,2-glycosidic linkage in sucrose.
Hence, sucrose does not undergo reaction characteristic to
aldehydes and ketones so it is called a NON-REDUCING
sugar.
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Handouts
α-1,2-Glycosidic bond
