Carbohydrate chemistry - continued Flashcards
1
Q
General formula of polysaccharides :
A
(C6H10O5)n
2
Q
What type of energy do polysaccharides provide?
A
Storage form of energy
3
Q
What type of function do polysaccharides give?
A
Structural function
4
Q
What are polysaccharides hydrolysed by?
A
Polysaccharides are hydrolysed by acid or enzymes to yield
monosaccharides
5
Q
What are the classes of polysaccharides?
A
Homopolysaccharides : STORAGE Starch Glycogen STRUCTURAL Cellulose Chitin
Heteropolysaccharides 1. Glycoproteins 2. Glycolipids 3. Peptidoglycans 4. Glycosamino- glycans 5. Proteo-glycans
6
Q
Define and give examples of Homopolysaccharides or homoglycans:
A
When only 1 type of monosaccharide units are
present in a polysaccharide molecule that is called
homopolysaccharide or homoglycans such as-glycogen in animals, starch and cellulose in plants.
7
Q
Define and give examples of Heteropolysaccharides or heteroglycans:
A
When 2 or more different types of monosaccharides are
present in a polysaccharides that is called
heteropolysaccharides or heteroglyccans such as-Glycoproteins, Glycolipids, Peptidoglycans,
Glycosaminoglycans, Proteoglycans etc.
8
Q
Homopolysaccharides - Starch is a major food source of carbohydrate. Where is starch found?
A
Starch is available in cereals, potatoes, legumes and vegetables and
called storage polysaccharide
9
Q
What is the end product of photosynthesis?
A
Starch is the end product of photosynthesis
10
Q
Which carbohydrate is a source of fuel or energy in plant growth and respiration
A
Starch is a source of fuel or energy in plant growth and respiration
11
Q
How much starch does an adult human consume daily?
A
Adult humans consume about 300 g starch daily
12
Q
What are the major constituents of starch?
A
The major constituents of starch :
amylose[98%] and amylopectin[amylopectin[2%]
13
Q
List the properties of Amylose[98%].
A
- Amylose is a linear polymer of 100-1000 glucose units
- Amylose is Linked with a α (1- 4) glycosidic bonds
- Amylose has non-reducing and reducing end
- Molecular weight varies from few 1000 to 150 000
- Amylose gives blue colour with iodine
14
Q
List the properties of amylopectin[2%].
A
- Highly branched polymer of glucose
- Branch points are located approximately at every 24
- 30 glucose units
- Produce purple to red colour with iodine
- Each branch point has an α (1- 6) glycosidic linkage
- Helix form interrupt the colour formation with iodine
15
Q
What type of polysaccharide is glycogen?
A
Glycogen is a storage polysaccharide in animals
16
Q
Glycogen is a source of…
A
fuel or energy in humans and animals
17
Q
What is glycogen also called?
A
Glycogen is also called animal starch
18
Q
Describe glycogen.
A
Glycogen is a highly branched polysaccharide of glucose units linked by α (1-
4) and α (1- 6) linkages (like amylopectin).
19
Q
What is the difference between glycogen and amylopectin?
A
Glycogen is more highly branched than amylopectin having
branch points in every 8-12 glucose units
20
Q
How many glucose units can be present in 1 glycogen molecule?
A
Up to 50 000 glucose units can be present in
one glycogen molecule and non-reducing in nature
21
Q
Depending on the nutritional status glycogen contributes..
A
10% weight of the liver and 2% weight of the muscle tissues.
22
Q
What leads to the formation of helix in glycogen?
A
A high number of
branch points in
glycogen make
this helix
23
Q
Cellulose is a major constituent of … and accounts for…
A
the plant cell wall and accounts for up to 50% of
the organic biosphere.
24
Q
Describe cellulose.
A
Cellulose is a linear homo-polysaccharide of D-glucose linked by β (1 – 4) glycosidic bonds
* Usually consists of 300 – 15 000 glucose units
25
Describe the structure of cellulose.
```
Cellulose has a structure of parallel
chains linked by H2 bonds
Several chains lie side by
side to form a stable fibrous
network by intra- and inter-chains hydrogen bonds
```
26
State the solubility of cellulose in water and state where it is used.
Cellulose is insoluble in water and used in manufacturing paper, cardboard,
insulating tiles, packaging materials, building materials etc.
27
What is the difference between cellulose and starch?
In contrast to starch, the β (1 – 4) glycosidic bonds of cellulose
are resistant to hydrolysis and are not
hydrolysed by the amylases.
28
The glycosidic bonds of Cellulose are resistance to hydrolysis. What is the exception?
Ruminants are in important exception, however,
since the bacteria that reside within the rumen
secrete cellulase, a β-glucosidase, that catalyzes
the hydrolysis of cellulose.
29
Which other organism can degrade cellulose? State how this is possible.
Termites can also degrade cellulose because
their digestive tract contain a parasite
(unicellular cilliate) that secretes cellulase.
30
Chitin is the second..
abundant organic compound on the earth
31
Describe chitin.
Chitin is a linear homo-polysaccharide of N-Acetyl-D-glucosamine
residues linked by β (1 – 4) linkages
32
Compare chitin with cellulose.
Chitin also forms extended fibres like cellulose
33
Chitin is indigestible by which type of animals?
Chitin is indigestible by vertebrate animals
34
Chitin is the principal constituent of which organism?
```
Chitin is the principal constituent of the outer shell of
arthropods, such as-
* Insects
* Crabs
* Beetles
* Lobsters
* Shrimp, prawns and cray fish etc.
```
35
Heteropolysaccharides are classified into several classes based on the chemical structure. Name those classes.
1. Glycoproteins
2. Glycolipids
3. Peptidoglycans
4. Proteoglycans
5. Glycosamino-glycans
36
Describe the structure of glycoproteins.
```
Oligo- or poly-saccharides are
covalently bound with proteins.
The Carbohydrate chain is varies in
length from 1 to >30 residues and
account for about 80% of the total mass
```
37
What does the carbohydrate of glycoproteins contain?
The carbohydrate part of glycoproteins
can contain up to four branches and
are O-linked to serine or threonine,
or N-linked to asparagine.
38
What do the protein part of glycoproteins contain?
```
The protein part[of glycoproteins] consists of divers group of proteins, such as-
Enzymes
Hormones
Structural proteins
Transport proteins
```
39
What are the carbohydrate units joined by?
The carbohydrate units can be joined by either
| α- or β-glycosidic linkage
40
Where can the linkage join?
The linkage can join between C1 of one sugar and
| C2, C3, C4 and C6 of another hexose sugar
41
Where do glycolipids get their name from?
Oligo- or short chain polysaccharides are covalently
| bound with lipids
42
State how glycolipids are placed in the bacterial cell wall and in the human plasma membrane.
These linear polymers are placed side by side in the bacterial
cell wall and in the human plasma membrane (5%).
43
What do peptidoglycans link to?
Peptidoglycans link to small peptides
44
Peptidoglycans are the rigid component of...
bacterial cell wall
45
What do peptidoglycans consist of?
Peptidoglycans consist of Alternating β (1 – 4) linkage between N-Acetyl-Glucose
(GlcNAc) and N-Acetyl-Muramic acid (MurNAc)
46
How are peptidoglycans placed in the cell wall?
These linear polymers are placed side by side in the cell wall
and are cross-linked by short peptides
47
What are cross - linked peptidoglycans degraded by?
These cross-linked peptidoglycans are degraded by and
| enzyme lysozyme
48
What does the enzyme lysozyme hydrolyse?
Enzyme lysozyme hydrolyses the glycosidic bond
| between monosaccharides and kills bacteria.
49
Where is lysozyme present?
Lysozyme is present in the tears, presumably a defence
| against bacterial infection of the eyes.
50
What are glycosaminoglycans?
Glycosaminoglycans are a complex of proteins and a class of polysaccharides
51
Where are glycosaminoglycans usually located?
Glycosaminoglycans are usually located in the extracellular space of animal tissues,
called extracellular matrix
52
What do glycosaminoglycans act as?
Glycosaminoglycans act as a porous pathway for the diffusion of nutrients and
oxygen to the individual cells
53
What is the extracellular matrix composed of?
The extracellular matrix is composed of a interlocking networks
of heteropolysaccharides and fibrous proteins
54
Describe the structure of the glycosaminoglycans.
Glycosaminoglycans are a family of a linear polymer and are composed of repeating disaccharide units
55
What is hyaluronic acid or hialuronate?
Hyaluronic acid (/ ˌhaɪ.əljʊəˈrɒnɪk /; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues.
56
What does hyaluronic acid contain at physiological pH?
At physiological pH hyluronic acid contains alternating units of
D-glucoronic acid and N-Acetyl glucosamine.
57
What is the molecular weight of hyaluronate?
Molecular weight of hyaluronate is >1 million
58
What is hyaluronidase? What does it do?
Hyaluronidase, an enzyme secreted by some
pathogenic bacteria, makes tissue more
susceptible to bacterial invasion and infection.
59
What hydrolyses the the outer glycosaminoglycans coat?
A similar enzyme in sperm, hydrolyses the outer
glycosaminoglycans coat around the ovum of
many organisms allowing sperm penetration.
60
OXIDATION OF SUGARS - What other way can a carbohydrate be classified?
Apart from usual classification, carbohydrate may also
| classify as reducing or non-reducing sugars
61
Which polysaccharides are regarded as non - reducing? Why?
All polysaccharides such as- starch, glycogen, cellulose,
chitin are regarded as non-reducing since they have only
one reducing end
62
Which disaccharides are non-reducing sugars?
On the other hand, among disaccharides, sucrose is the only
non-reducing sugar and all other mono- and disaccharides
are considered as reducing sugars
63
What do reducing sugars usually have?
Reducing sugars usually have a potentially active free
aldehyde (-CHO) or free ketone (=C=O) group or free
anomeric carbon in their structures which have reducing
property
64
How does a reducing sugar works/ oxidize?
The reducing properties of sugars are usually observed by their
ability to reduce the metal ions such as Cu2+, Ag+, Bi3+ in
alkaline condition
This properties are used to analyse both qualitative
analyses of sugars.
65
What do reducing sugars form in a mild alkaline condition?
Reducing sugars form different endiols in a mild alkaline condition
66
Describe the endiol forms of sugars.
These endiols forms of sugars are highly reactive
intermediates which are readily oxidized and reduce
oxidizing metal ions such as Cu2+, Ag+, Bi3+
This properties are used to detect reducing sugars in
biological samples.
67
What is the Benedict's test sufficiently sensitive?
The Benedict's test is sufficiently sensitive to detect
| reducing sugar in diabetic urine or in any sample.
68
What do the endiol forms of sugars reduce?
These endiols forms of sugars reduce the cupric ion (Cu2+)
to cuprous ion (Cu+) which is less soluble in water and that
is why a precipitate of cuprous oxide (Cu2O) is formed
which yellow/ orange/ red in colour.
69
What is the reducing sugar oxidized to?
The reducing sugar is in turn oxidized to the corresponding
| carboxylic acid e.g. glucose converted to gluconic acid.
70
What happens if any anomeric carbon of the one monosaccharide unit of a disaccharide is involved in the glycosidic bond?
If any anomeric carbon of the one monosaccharide unit of a
disaccharide is involved in the glycosidic bond then it
cannot be oxidized
71
Why is maltose or lactose a reducing sugar?
On the other hand, the anomeric carbon of another
monosaccharide is remained free which can easily oxidized
by meta ions, which is the case for maltose and lactose.
Hence, they are reducing sugars.
72
Sugar with mineral acids:
| Monosaccharides are generally stable in...
dilute mineral
| acids even on heating.
73
What happens when aldohexose or aldopentose and ketose sugars are
heated with strong concentrated mineral acids such as
sulfuric acid?
When aldohexose or aldopentose and ketose sugars are
heated with strong concentrated mineral acids such as
sulfuric acid , all carbohydrates are dehydrated forming
appreciable amount of furfural or its derivatives.
74
What does the latter condense with?
The latter condense with α-napthol and other phenolic
| compounds to give highly coloured pink to violet complex.
75
The steps above indicate that this
reaction is called Molisch Test and is used for the
| detection of all kinds of carbohydrates.
76
What happens in the case of di- , oligo- and polysaccharides?
In case of di-, oligo- and polysaccharides, sulfuric acid first
hydrolyzes the glycosidic bonds to produce
monosaccharides then make them dehydrated to form
furfural and its derivatives. Hence, the reaction is slower.
77
Chain elongation/ Killian Fisher Reaction: What is the cyanohydrin synthesis or Killian Fisher reaction
The cyanohydrin synthesis or Killian Fisher Reaction is a
process by which the chain length of a an aldose sugar is
increased by one carbon atom and 2 new aldose can be
formed.
78
List the 3 steps of the chain elongation/Killian Fisher reaction.
1. Cyanohydrin synthesis
2. Hydrolysis
3. Reduction
79
Briefly describe each step of the chain elongation/Killian Fisher reaction.
1. Aldehydes react with hydrogen cyanide (HCN) to form
cyanohydrins which forms a new asymmetric centre.
2. Subsequent hydrolysis yields carboxylic acids (aldonic
acid) containing one extra
carbon than the original
sugar.
3. Reduction (Na/Hg) yields
a mixture of 2 aldose
sugars containing one
more carbon
80
Chain shortening/ Wohl Reaction:
| * Chain shortening is also 3 steps reaction. List the 3 steps.
1. Oxime formation
2. Acetylation
3. Wohl reaction
81
Briefly describe each step of the chain shortening/Wohl reaction.
```
1. Hydroxylamine (NH2OH) reacts with both aldoses and
ketoses to form oximes.
2. If the sugar
oxime is treated
with acetic-
anhydride (Ac2O)
cyanohydrin form
via dehydration
3. Treatment with
AgNO3 and NH3
results an aldose
with lower carbon
(Wohl reaction)
```
82
Where does aldol condensation occur frequently?
This reaction frequently occurs in carbohydrate
| biochemistry.
83
Briefly describe what happens in aldol condensation.
One ketose sugar and another aldose sugar are joined
together to form long carbon chain sugar by a
nucleophile/anion (-) and electrophile/cation (+)
formation, respectively.
84
There are 3 analytical methods available for studying the
| periodate oxidation of polyhydroxy compounds. These are:
1. Iodometric
2. Acidimetric
3. Spectrophotometric
85
Which analytical method do the reactions below deal with?
The reactions below deal with the iodometric technique.
86
What happens to the Compounds containing hydroxyl groups on adjacent carbon
atoms?
C[ompounds containing hydroxyl groups on adjacent carbon
atoms are qualitatively oxidized at room temperature by an
excess of periodic acid or its salts.
87
```
Periodic acid (HIO4) is
very useful in
```
CARBOHYDRATE ANALYSIS
88
Briefly describe periodate oxidation.
Periodic acid (HIO4
) will cleave C—C bonds if both carbons
have hydroxyl groups or if one carbon having a hydroxyl
group is adjacent to another carbon with an amino group or
keto or aldo oxygen. Every cleavage results in an oxidation.
The carbon participating in the cleavage reaction is oxidized
to the next level (e.g. alcohol to aldehyde AND aldehyde to
carboxylic acid).
89
What happens if the hemiacetal C is involved in a glycosidic
| linkage or is methylated?
However if the hemiacetal C is involved in a glycosidic
linkage or is methylated, the sites of possible cleavage are
reduced due to the inability to open-out the ring structure
