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Introduction to biomolecules - BIOC201 > Carbohydrate chemistry > Flashcards

Carbohydrate chemistry Flashcards

1
Q

What is the general formula for disaccharides?

A

(C12H22O11)

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2
Q

What is the general formula for polysaccharides?

A

(C6H10O5)n

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3
Q

What is the general formula for monosaccharides?

A

(CH2O)n

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4
Q

What do carbohydrates consist of?

A

An aldehyde , OR a ketone group with 2 or more hydroxyl groups

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5
Q

What type of sugar is glucose

A

An aldohexose sugar

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6
Q

Ribulose is an example of a…

A

Keto - pentose sugar

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7
Q

Hemiketal formation is a reaction between :

A

A ketone and alcohol

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8
Q

Hemiacetal formation is a reaction between:

A

An aldehyde and alcohol

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9
Q

What type of ring does fructose form during hemiketal formation?

A

A furanose ring

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10
Q

Name the epimers of glucose.

A

Mannose and galactose

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11
Q

How many carbons are present IN a pyranose ring?

A

5

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12
Q

List the storage polysaccharides.

A

Starch[Plant polysaccharide]

Glycogen

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13
Q

List the structural polysaccharides.

A

Cellulose[plant polysaccharide]

Chitin[animal polysaccharide]

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14
Q

List the heteropolysaccharides.

A

Peptidoglycans , glycoproteins , glycolipids , glycosaminoglycans , Proteo - glycans

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15
Q

what are the major constituents of starch?

A

amylopectin(2%) and amylose(98%)

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16
Q

what is found in glycosaminoglycans?

A

D-glucoronic acid

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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
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18
Q

Chitin is a homo - polysaccharide of :

A

N-Acetyl-D-Glucosamine residues

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19
Q

What are the N-Acetyl-D-Glucosamine residues linked by?

A

Beta(1,4) linkages

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20
Q

Cellulose forms a stable fibrous network linked by:

A

Hydrogen bonds

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21
Q

Which glycosidic bonds are present in amylopectin?

A

alpha (1 - 6) and alpha (1 - 4) glycosidic linkages

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22
Q

Concentration of glycogen in the liver and muscle is usually ……………% and …………….% of their total weights, respectively.

A

Liver - 10% ; muscle - 2%

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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.

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24
Q

The disease ‘Multiple sclerosis’ is called so because……………….

A

multiple plaques form in the myelin sheath of neuronal cells

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25
Q

Carbohydrates are essential components of all living organisms such as-

A 
 Humans
 Plants
 Animals
 Bacteria
 Viruses
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26
Q

What are carbohydrates defined as?

A

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.

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27
Q

Chemistry of carbohydrates :

A

Carbohydrates have one aldehyde (-CHO) or ketone (=C=O) group
with two or more hydroxyl (-OH) groups in their structures.

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28
Q

Carbohydrates are classified into 4 major classes based on the number of monomeric units present. Name the 4 major classes

A
  1. Monosaccharides
  2. Disaccharides
  3. Oligosaccharides
  4. Polysaccharides
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29
Q

What are monosaccharides?

A

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

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30
Q

Every individual monomeric unit of carbohydrate is called

A

Monosaccharide - glucose , fructose , galactose , ribose[in RNA] , deoxyribose[in DNA] , etc.

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31
Q

Monosaccharides can be sub-divided into several classes
depending on the number of carbon atoms present in their
structures such as -

A

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

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32
Q

Define the term ‘disaccharides’

A

Disaccharides are carbohydrates that can be hydrolysed into 2 molecules of the same or different monosaccharides

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33
Q

Sucrose is the most …

A

Abundant disaccharide

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34
Q

Where is sucrose synthesized?

A

Sucrose is synthesized mainly in plants such as - sugarcane , sugar beet , etc.

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35
Q

Lactose is a major disaccharide that comes from …

A

milk

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36
Q

What is released during the hydrolysis of starch?

A

Maltose is released from the hydrolysis of starch, a plant

polysaccharide.

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37
Q

What is cellobiose?

A

Cellobiose is the repeating disaccharide in cellulose

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38
Q

Where is cellulose found?

A

Cellulose is found only in the plant world.

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39
Q

What is the difference between maltose and cellobiose?

A

The difference between maltose and cellobiose is only in
the glycosidic link
maltose - alpha[1,4] glycosidic bond
cellobiose - beta[1,4] glycosidic bond

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40
Q

What is the general formula of disaccharides and where does it come from?

A

The general formula of disaccharides is: C12 H22O11 which

comes from C12H24O12 – H2O (dehydration)

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41
Q

maltose hydrolysis products :

A

D-glucose + D-glucose

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42
Q

sucrose hydrolysis products :

A

D-glucose + D-fructose

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43
Q

lactose hydrolysis products :

A

D-glucose + D-galactose

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44
Q

cellobiose hydrolysis products:

A

D-glucose + D-glucose

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45
Q

What are oligosaccharides?

A

Oligosaccharides are carbohydrates that can be hydrolyzed into 3 – 20 of
the same or different monosaccharide units such as - Fructooligosaccharide (FOS),
Galactooloigosaccharides (GOS).

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46
Q

what are polysaccharides?

A

Polysaccharides are carbohydrates that can be hydrolyzed into more than
20 monosaccharides units such
as – starch, cellulose (plant polysaccharides), glycogen,
chitin (animal polysaccharide).

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47
Q

What are isomers?

A

Isomers are molecules that consist of the same number and kinds of
atoms but differ in their structure or spatial configurations

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48
Q

Isomers of carbohydrates are classified into two

different classes, such as -

A

i. Structural isomers

ii. Optical isomers or stereo-isomers

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49
Q

What are structural isomers?

A

Structural isomers are compounds that have the same molecular formula but
differ in structural formula

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50
Q

The structural isomerism of carbohydrates can be shown

into two different ways, such as -

A

a) Aldose-Ketose isomerism

b) Pyranose-Furanose Ring isomerism

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51
Q

Briefly describe aldose - ketose isomerism.

A

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
Q

Briefly describe pyranose - furanose isomerism.

A

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
Q

The pyranose and furanose are the ring structure of

A

ALDOSE and KETOSE sugar, respectively

54
Q

Glucose and fructose are usually in..

A

straight chain form

55
Q

The predominant form of glucose and fructose in solution is …

A

Is not open - chain structures

56
Q

What did the English chemist WN Haworth show?

A

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
Q

How does glucose , fructose and some other sugars react?

A

they react internally to form cyclic

HEMIACETALs or HEMIKETALS.

58
Q

What are the ring structures of aldose and ketose sugars called?

A

The ring structures of aldose and ketose sugars are

also called HAWORTH PROJECTION.

59
Q

What is hemiacetal formation?

A

Hemiacetal formation is a characteristics reaction between

aldehyde and alcohols

60
Q

Briefly describe pyranose ring formation[hemiacetal formation].

A

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
Q

What is hemiketal formation?

A

Hemiketal formation is a characteristics reaction between

ketone and alcohols

62
Q

Briefly describe Furanose ring formation[hemiketal formation].

A

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
Q

What is an optical or stereo- isomer?

A

Optical or stereo - isomers are compounds that have the same structural formula but
differ in spatial configuration

64
Q

What causes stereo-isomer formation to occur?

A

Stereo-isomer formation occurs due to the presence of

asymmetric/ chiral center/ chiral carbon atoms.

65
Q

What is an asymmetric carbon?

A

An asymmetric carbon is a carbon atom to which 4 different atoms or groups of
atoms are attached

66
Q

All monosaccharides have one or more asymmetric or chiral carbon atoms except

A

dihydroxyacetone

67
Q

How many asymmetric/chiral carbon atoms does D- or L- glyceraldehyde have?

A

D- or L-glyceraldehyde each of them have

one asymmetric/ chiral carbon atom.

68
Q

What are enantiomers?

A

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
Q

What are epimers?

A

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
Q

What are the most important epimers of glucose[biologically]?

A

Biologically the most important epimers of glucose are:
galactose and mannose, formed by epimerization at carbon
number 2 and 4 respectively.

71
Q

Why are D-Mannose and D-Galactose called diastereomers?

A 
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
Q

What is an anomer?

A

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
Q

Which carbon from the straight chain form becomes an

asymmetric centre in the ring form of glucose?

A

C1 from the straight chain form becomes an

asymmetric centre in the ring form of glucose

74
Q 
Two different structures are formed based on this 
asymmetric carbon (C1), For example -
A

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
Q

What are the alpha and beta forms of glucose called? Which carbon is the anomeric carbon?

A

These α and β forms of carbohydrate
(glucose) are called anomers and C1 is
called the anomeric carbon

76
Q

What is an anomeric carbon?

A

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
Q

What confers the optical activity on the compounds?

A

The presence of an asymmetric carbon confers the optical activity on the compounds

78
Q

Why are optical isomers called enantiomers ?

A

Optical isomers are also mirror image to each other hence
they are ENANTIOMERS.
 These compounds are seem like the left and right hand

79
Q

Enanatiomers have similar properties e.g.

A 
These compounds have similar properties e.g. 
◦ Same boiling point
◦ Same melting point
◦ Same solubility and so on 
but different optical activity
80
Q

The enantiomers are simply named -

A

These two compounds are simply named as Dextrorotatory
or D and Levorotatory or L. For example- D-Alanine and L-
Alanine.

81
Q

Briefly describe dextrorotatory or D(+)

A 
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
Q

Briefly describe Levororotatory or L(-)

A 
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
Q

In which direction does an optically active compound rotate the plant of polarized light?

A

An optically active compound rotates the plant of polarized

light either RIGHT or LEFT direction.

84
Q

What is specific/optical rotation?

A

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
Q

The specific rotation is..

A

a standard measure degree of the

compound which is dextrorotatory or leverotatory

86
Q

Describe the specific rotation of dextrorotatory and Levororotatory.

A

Dextrorotatory compounds have positive (+ve) specific
rotation while levorotatory compounds have negative (-ve)
specific rotation.

87
Q

what do 2 enantiomers have?

A

Two enantiomers have equal and opposite specific rotation.

88
Q

What is the specific rotation of D- and L- Bromobutane?

A 
D-bromobutane = +23.1 degrees Celsius 
L-bromobutane = -23.1 degrees Celsius
89
Q

What is the specific rotation of alpha and beta - D - glucose?

A

α-D(+) glucose = +112 degrees Celsius

β-D(+)-glucose = +19 degrees Celsius

90
Q

What happens when alpha - and beta - forms of a compound are dissolved in water?

A

The specific rotation of each form of the compound
gradually changes with time and approach to final
equilibrium value that is called MUTAROTATION.

91
Q

What is mutarotation?

A

Mutarotation is the gradual change of optical rotations of two
compounds, which continues until equilibrium is
established, is known as MUTAROTATION

92
Q

What is the mutarotation of α-D(+) glucose = +112 degrees Celsius[specific rotation] and
β-D(+)-glucose = +19 degrees Celsius[specific rotation] mixture?

A

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
Q

Why is mutarotation significant?

A

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
Q

What happens if α-D-glucose and β-D-glucose are dissolved

in ethylalcohol and then allowed to crystallize?

A

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
Q

What happens if α-D-glucose and β-D-glucose are dissolved in acetic acid
and then allowed to crystallize?

A

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
Q

What are disaccharides?

A

Disaccharides are natural carbohydrates usually contain more than one
monosaccharide units.

97
Q

What do monosaccharides tend to do?

A

Monosaccharides have a tendency to reach to hydroxyl

compounds to form stable acetals called GLYCOSIDES.

98
Q

How are these glycosides classified?

A

These glycosides are classified according to the sugars they are derived from such as -
 Glucoside from glucose
 Galactoside from galactose etc.

99
Q

What is the linkage between 2 monosaccharide units called?

A 
The linkage (-C-O-C-) between two monosaccharide units 
is called a glycosidic or galactosidic linkage
100
Q

How are disaccharides formed?

A

When two monosaccharide units are joined to each other by a

glycosidic or galactosidic linkage

101
Q

All disaccharides have the same molecular formula which is

C12H22O11 and hence…

A

They are structural isomer to one

another.

102
Q

List the common disaccharides

A

Maltose
Sucrose
Lactose
Cellobiose

103
Q

List the hydrolysed products/compositions of each disaccharide.

A
  • Maltose = D-glucose + D-glucose
  • Sucrose = D-glucose + D-fructose
  • Lactose = D-glucose + D-galactose
  • Cellobiose = D-glucose + D-glucose
104
Q

What is maltose formed by?

A

Maltose is formed by the action of enzyme

  • Diastase in plants and
  • Ptyalin in animals
105
Q

What is the hydrolysis of maltose catalysed by and what does it yield?

A

The hydrolysis of maltose is catalysed by the enzyme MALTASE
and yields glucose units only

106
Q

How are the 2 α-D-glucopyranose components joined?

A

The TWO α-D-glucopyranose components are joined head-to-tail through C1 of one glucose molecule and C4 of second
glucose molecule.

107
Q

What is the linkage between the glucose units of maltose?

A

The linkage is α-1, 4-GLUCOSIDIC linkage.

α (1,4) glycosidic bond

108
Q

Is maltose a reducing sugar?

A

Yes

109
Q

What is lactose exclusively associated with?

A

Lactose is exclusively associated with animal kingdom

110
Q

What lactose also called?

A

Lactose is also called MILK carbohydrate such as- in human milk:
5-8% and Cow milk: 4-6%.

111
Q

Briefly describe the hydrolysis of lactose.

A

Lactose can be hydrolyzed by dilute mineral acid or by
enzyme LACTASE to yield equal concentrations of D-glucose
and D-galactose.

112
Q

What are the monosaccharide units of lactose joined by?

A

The monosaccharides units of lactose are joined by a β-1, 4-

galactosidic/glycosidic linkage.

113
Q

What is the α-form of lactose is used to prepare?

A

The α-form of lactose is used to prepare INFANT FOOD and

PENICILLIN.

114
Q

What specific rotation does the equilibrium mixture of the α- and β-form of lactose have?

A

The equilibrium mixture of the α- and β-form of lactose has

a specific rotation of +55 degrees Celsius.

115
Q

What is cellobiose a stereoisomer of?

A

Cellobiose is a stereoisomer of maltose

116
Q

What cellobiose a product of?

A

Cellobiose is a product of the hydrolysis of cellulose polysaccharide

117
Q

What does cellobiose contain?

A

Cellobiose contains TWO glucose units, which are joined by

β-1, 4-glycosidic bond.

118
Q

List one similarity between maltose and cellobiose.

A

They are both reducing sugars that undergo mutarotation

119
Q

What is sucrose usually obtained from?

A

Sucrose is usually obtained from sugarcane and sugar beet.

120
Q

Sucrose is the most

A

widely used sweetening agent in the world

121
Q

Where is sucrose synthesized?

A

Sucrose is synthesized in all photosynthetic plants.

122
Q

What does sucrose consist of?

A

Sucrose consists of ONE molecule of α-D-glucopyranose (glucose)
and ONE molecule of β-D-fructofuranose (fructose).

123
Q

Briefly describe the formation of a sucrose molecule.

A

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
Q

What is the glycosidic bond of sucrose hydrolysed by?

A

This glycosidic bond of sucrose can be hydrolyzed by
mineral acids (e.g. H2SO4 or HCl) or by the enzyme
SUCRASE (invertase).

125
Q

Sucrose does not show mutarotation, why?

A

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
Q

Sucrose is a non-reducing sugar, why?

A

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.
Page 13 in
Handouts
α-1,2-Glycosidic bond

Introduction to biomolecules - BIOC201 (6 decks)

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