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MB prep: Biochemistry. > Chemistry of carbonhydrates. > Flashcards

Chemistry of carbonhydrates. Flashcards

1
Q

What is the general formula of carbohydrates

A

Cn(H2O)n

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2
Q

What are the classifications of carbonhydrates?

A

Monosaccharides
Disaccharides
Polysaccharides
Oligosaccharides

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3
Q

What are monosaccharides?

A

Also known as simple sugars, they are sweet to taste and soluble in water. They contain only one
polyhydroxy aldehyde or ketone unit and cannot be hydrolyzed.

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4
Q

What are the various ways we can classify monosaccharides?

A

Depending on the number of carbon units
Depending on the functional group present

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5
Q

An aldose carbonhydrate with 3 carbon units is:

A

Glyceraldehyde

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6
Q

Glucoheptose is what kind of sugar (aldose or ketose), how many carbon units?

A

7, aldose

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7
Q

A ketose sugar with 7 Carbon units is

A

Sedoheptulose

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8
Q

A ketose sugar of 6 carbon units is called

A

Fructose

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9
Q

A ketose sugar of 3 carbon units is called what

A

Dihydroxyacetone

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10
Q

An aldose sugar with 6 carbon units

A

Glucose, Galactose and Mannose

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11
Q

An aldose sugar with 4 carbon units

A

Erythrose

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12
Q

An aldose sugar with 5 C’s

A

Ribose, Xylose

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13
Q

A ketose sugar with 4 C’s

A

Erythrulose

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14
Q

A ketose sugar with 5 C’s

A

Xylulose, Ribulose

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15
Q

What type of monosaccharide with example is involved in pentose phosphate pathway

A

Heptose (Seheptulose)

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16
Q

What monosaccharides are intermediate products in the pentose phosphate pathway

A

Ribose and Ribulose

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17
Q

What is the function of Ribose

A

constituent of RNA and coenzymes (ATP, NADP, FAD)
Intermediate products of pentose phosphate pathway

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18
Q

What monosaccharide is a constituent of proteoglycans and glycoproteins

A

D-Xylulose

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19
Q

What is the function of L-Xylulose

A

An intermediate in uronic acid pathway

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20
Q

What is a constituent of glycoproteins, glycolipids and blood group substances

A

D- Mannose

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21
Q

Which is a precursor of glycerol

A

Dihydroxyacetone

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22
Q

Which is an intermediate in glycolysis

A

glyceraldehyde

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23
Q

Which is an intermediate product of carbonhydrate metabolism (Hexose Monophosphate Shunt)

A

D-Erythrose

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24
Q

What are some functions of D-Galactose you know?

A

Converted to glucose in liver and metabolised
Synthesized in the breast to make lactose of milk
constituent of glycolipids, proteoglycans and glycoproteins

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25
Q

What is Sialic acid?

A

An N-acyl or O-acyl derivative of neuraminic acid.

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26
Q

What is the major Sialic acid?

A

N-acetyl Neuraminic acid (NANA) <Neuraminic></Neuraminic>

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27
Q

Sialic acid is a constituent of what?

A

Both Glycoprotein and Ganglioside

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28
Q

Draw out Sialic acid

A

Refer to drawing 5 in booklet

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29
Q

Fructose exists predominantly as what ring structure

A

Furanose ring (Fructofuranose)

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30
Q

Glucose exists predominantly as what ring structure

A

Pyranose ring (Glucopyranose)

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31
Q

Draw Pyran and Furan

A

Refer to drawing 6 in booklet

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32
Q

What are some natural sources of fructose

A

Fruit juice, honey, sugarcane, seminal fluid

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33
Q

What is the molecular formula for Disaccharides

A

[Cn(H2O)n-1

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34
Q

What are Disaccharides?

A

They are crystalline, soluble and sweet to taste and are basically 2 monosaccharide linked by a glycosidic bond. They will release 2 monosaccharides on hydrolysis.

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35
Q

What are the classifications of disaccharides

A

NonReducing disaccharides (the functional groups are involved in the glycosidic bond are thus not free)
Reducing Disaccharides (Free functional group)

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36
Q

List the reducing disaccharides

A

Maltose, Isomaltose, Lactose, Lactulose

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37
Q

List the non reducing disaccharides

A

Sucrose, Trelahose

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38
Q

What constitutes Maltose

A

aDglucose+aDglucose

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39
Q

What constitutes Isomaltose

A

aDglucose+aDglucose

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40
Q

What constitutes Lactose

A

D Galactose+ bD glucose, (b1-b4 linkage)

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41
Q

What constitutes Lactulose

A

aD Galactose+ bD Fructose

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42
Q

What is the glycosidic linkage of maltose

A

(a1- a4 linkage)

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43
Q

What is the glycosidic linkage of isomaltose

A

a1-a6 linkage

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44
Q

What is the glycosidic linkage of Lactose

A

b1-b4 linkage

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45
Q

what is the glycosidic linkage of lactulose

A

a1-b4 linkage

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46
Q

what are the sources of trelahose

A

sugar of insect hemolymph, yeast and fungi

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47
Q

sources of sucrose are

A

sugarcane

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48
Q

What are the constituents of trelahose

A

aDglucose + aDglucose

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49
Q

What are the constituents of trelahose

A

aDglucose + aDglucose

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50
Q

what are the constituents of sucrose

A

aDglucose + bD Fructose

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51
Q

what are the glycosidic linkage of sucrose

A

a1-b2 linkage

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52
Q

what is the glycosidic linkage of trelahose

A

a1-a1 linkage

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53
Q

What are the functions of lactulose

A

Osmotic sedative
Not hydrolyzed but fermented by intestinal bacteria
Mainly synthetic (small amounts in heated milk)

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54
Q

What are oligosaccharides?

A

carbonhydrates with 3-10 monosaccharide units

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55
Q

Blood group substances are what kind of carbonhydrate

A

Oligosaccharides

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56
Q

What are oligosaccharides usually in conjugation with?

A

Proteins (Glycoproteins and Proteoglycans) and Lipids (Glycolipids)

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57
Q

What are polysaccharides

A

Carbs with > 10 monosaccharide chains

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58
Q

What are the types of polysaccharides

A

Homoglycans (Homopolysaccharides) and Heteroglycans (Heteropolysaccharides)

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59
Q

What are Homoglycans

A

Carbonhydrates with 1 type of monosacchararide

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60
Q

What are Heteroglycans

A

Carbohydrates with 2 or more types of monosaccharides

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61
Q

List examples of Homoglycans

A

Glycogen, cellulose, dextran, inulin(fructosan), starch, chitin.

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62
Q

List examples of Heteroglycans

A

Glycosaminoglycans(Mucopolysaccharides), Pectin, agarose, agar

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63
Q

The storage form of glucose in plants is, animals is?

A

starch, glycogen

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64
Q

What constitutes starch

A

amylose(13-20%) and amylopectin(80-87%)

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65
Q

Describe the structure of amylose

A

soluble unbranched chain, with a1-4 glycosidic linkage

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66
Q

Describe the structure of amylopectin

A

insoluble branched chain with a1-4 glycosidic linkage and a1-6 glycosidic linkage (at branches)

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67
Q

Describe Dextrin

A

Dextrin is a short chain polysaccharide formed by the partial hydrolysis of starch by aAmylase (enzyme). They have free aldehyde groups. It occurs in honey and is not fermented by yeast. They are used in food additives, textiles, adhesives, thickness and stabilizers.

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68
Q

Describe dextran

A

Dextran is a long chain polysaccharide (glycosidic linkages: a1-6,a1-4 and a1-3) produced by certain bacteria and used as a plasma volume expander in the treatment of shock. It is essentially called a Plasma Expnder. It is used as a dietary fiber supplement and a food thickner.

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69
Q

What are plasma expanders?

A

They are high molecular weight substances that exert osmotic pressure and maintain food in the vascular component.

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70
Q

Give examples of plasma expanders

A

Human albumin
dextran
hydroxyethyl starch
degraded gelatin polymer

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71
Q

Describe the structure of glycogen

A

made up of aDglucose. It has a1-4 glycosidic linkage at the linear chain and a1-6 glycosidic linkage at the branches

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72
Q

List functions of glycogen

A

Muscle glycogen is a storage form of energy within the muscles itself
Liver glycogen is important for the maintenance of blood glucose.

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73
Q

Where is chitin naturally found

A

exoskeletons of insects and crustaceans, and in mushrooms

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74
Q

describe the structure of chitin

A

Made up of N acetyl Glucosamine joined by b1-4 linkage

75
Q

What is the major component of cell wall

A

cellulose

76
Q

Describe the structure of cellulose

A

It is an insoluble unbranched polymer of bDglucose and consists of b1-4 glycosidic linkage. Humans cannot digest cellulose because we don’t have the enzyme that digests it, unlike herbivores

77
Q

What are the functions of cellulose

A

Cellulose is associated with the reduced incidence of: Cardiovascular disease, colon cancer, diverticulosis, diabetes
Cellulose is a dietary fiber used in the bulk of food. It aids intestinal motility, and helps produce smooth stool.

78
Q

Describe the structure of inulin(fructosan)

A

A fructose homopolysaccharide of b2-1 glycosidic linkage. It is readily soluble in water.

79
Q

What are sources of inulin

A

dahlias, chicoris, garlics, dandelions, onions

80
Q

What enzyme hydrolyzes inulin

A

INULINASE (not available in humans)

81
Q

What is the function of inulin

A

Used in clearance test to determine Glomerular filtration rate.

82
Q

Describe the structure of glycosaminoglycans

A

They are unbranched heteropolysaccharide chains composed of disaccharide repeat units. Each unit is composed of amino sugar (D-glucosamine or D-galactosamine) and uronic acid(L-glucuronic acid or its epimer L-iduronic acid.) I.e except in the case of keratan sulphate.
This polymer is attached covalently to extracellular
proteins called core protein (except hyaluronicacid) to form proteoglycans resulting in a structure that resembles a “bottle brush”. The proteoglycan monomer associates with a molecule of hyaluronic acid to form proteoglycan aggregates.The association is stabilized by additional small proteins called link proteins. With the exception of hyaluronic acid, all the GAGs contain sulfate group.

The amount of carbs in proteoglycans>Glycoproteins

83
Q

Why are glycosaminoglycans also called mucopolysaccharides

A

They were first isolated from mucin

84
Q

Draw the bottle brush structure of proteoglycan aggregate and proteoglycan monomer.

A

Refer to drawing 7 in booklet.

85
Q

Where are Glycosaminoglycans naturally found

A

Vitreous humor, Synovial fluid of joints, arterial walls, Bones,

86
Q

What are the 2 amino sugars involved in Glycosaminoglycans

A

D-glucosamine or D-galactosamine

87
Q

What are the 2 uronic acids involved in Glycosaminoglycans

A

L-glucuronic acid or its epimer L-iduronic acid

88
Q

List functions of Glycosaminoglycans

A

They are major components of the extracellular
matrix or ground substance.
GAGs carry sulfate and carboxyl groups which give
them a negative charge and have special ability to
bind large amounts of water, thereby producing a
gel-like matrix which functions as a cushion against
mechanical shocks.
They act as “molecular sieves”, determining which
substances enter and leave cells.
They also give resilience (elasticity) to cartilage,
permitting compression and re-expansion.
They lubricate joints both at the surface of cartilage
and in synovial fluid.
The viscous lubricating properties of mucous secretions are also due to the presence of glycosaminoglycans,

89
Q

List the types of glycosaminoglycans

A

Heparin, Condroitin sulphate, Heparin sulphate, Hyaluronic acid, Dermatan sulphate, Keratan sulphate.

90
Q

what is the disaccharide unit of hyaluronic acid

A

N-Acetyl glucosamine -Glucuronic acid

91
Q

what is the disaccharide unit of chondroitin sulphate

A

N-Acetyl-galactosamine-Glucuronic acid

92
Q

what is the disaccharide unit of keratan sulphate

A

N-Acetyl-glucosamine-Galactose

93
Q

what is the disaccharide unit of heparan sulphate

A

Glucosamine-Glucuronic acid or Iduronic acid

94
Q

what is the disaccharide unit of heparin

A

Glucosamine-Glucuronic acid or Iduronic acid

95
Q

what is the disaccharide unit of dermatan sulphate

A

N-Acetyl-galactosamine-L-lduronic acid

96
Q

what GAG has no uronic acid

A

keratan sulphate

97
Q

what GAG has no sulphate group

A

hyaluronic acid

98
Q

what GAG is not covalently linked to a protein

A

hyaluronic acid

99
Q

what GAG is found in bacteria

A

hyaluronic acid

100
Q

what GAG is most abundant

A

chondroitin sulphate

101
Q

what GAG is an anti coagulant

A

heparin

102
Q

where is the site of synthesis of GAG

A

E.R and Golgi body

103
Q

what is the shape of the proteoglycan monomer

A

bottle brush

104
Q

what GAG helps in cell migration

A

hyaluronic acid

105
Q

what GAGs help in compressibility of cartilage weight bearing

A

hyaluronic acid and chondroitin sulphate

106
Q

what GAGs help in corneal transparency

A

Dermatan sulphate and Keratan sulphate

107
Q

what GAG helps change selectiveness of renal glomerular membrane

A

Heparan sulphate

108
Q

what are some intracellular GAGs

A

Heparan sulphate in synaptic vesicles and Heparin in mast cells

109
Q

what is the function of hyaluronic acid

A

Serves as lubricant and shock absorber, facilitates cell migration in embryogenesis, morphogenesis, wound healing

110
Q

what is the function of heparin

A

Serves as an anticoagulant, causes release of lipoprotein lipase from capillary walls

111
Q

what is the function of heparan sulphate

A

Component of plasma membrane where it may act as receptor and may also participate in the mediation of cell growth, cell-to-cell communication

112
Q

what is the function of keratan sulphate

A

Transparency of cornea

113
Q

what is the function of dermatan sulphate

A

Transparency of cornea and maintains the overall shape of the eye

114
Q

what is the function of chondroitin sulphate

A

Provides an endoskeletal structure helping to maintain their shape. Has a role in compressibility of cartilage in weight bearing

115
Q

where is heparin found

A

Mast cells, Liver, lung, skin

116
Q

where is heparan sulphate found

A

Skin, Kidney basement membrane

117
Q

where is dermatan sulphate found

A

Skin

118
Q

where is chondroitin sulphate found

A

Cartilage, bone, CNS

119
Q

where is hyaluronic acid found

A

Skin, Synovial fluid, bone, cartilage, vitreous humor,loose connective tissue, umbilical cord.

120
Q

where is keratan sulphate found

A

Cornea, Cartilage, Loose connective tissue

121
Q

what are glycopoteins

A

Glycoproteins are proteins to which oligosaccharides are covalently attached to their polypeptide chain.Glycoproteins contain much shorter carbohydrate chain than proteoglycans.

122
Q

what is the difference between glycoprotein and proteoglycans

A

PROTEOGLYCANS are made of over 95% carbonhydrates. They have long unbranched oligosaccharides and they have repeating units of disaccharide.
WHILE
GLYCOPROTEINS are made of less than 4% carbohydrates, they have short highly branched oligosaccharides and they do not have repeating units of disaccharides

123
Q

what are proteoglycans

A

GAGs are covalently attached to a protein (termed Core Protein) to form hybrid molecules, called Proteoglycan. Proteoglycan molecules attached to core protein forming proteoglycan monomer. The shape of Proteoglycan monomers is Bottle brush. Several Proteoglycan monomer associate noncovalently to a Hyaluronic Acid by a link protein to form Proteoglycan Aggregate

124
Q

what are the chemical properties of monosaccharides

A
  1. Action of Strong Acids: Furfural formation
  2. Action of Alkalies: Enolization
  3. Oxidation: Sugar acid formation
  4. Reduction: Sugar alcohol formation
  5. Action of phenylhydrazine: Osazone formation.
125
Q

explain the action of strong acids function on monosaccharides

A

On heating a sugar with mineral acids (H2SO4 or HCI),
the sugar loses water and forms furfural derivatives.
These may condense with α-naphthol, thymol or
resorcinol to produce colored complexes. This is the
basis of the:
* Molisch’s test
* Seliwanoff’s test
* Bial’s test
* Tollen’s-phloroglucinol-HCI test.

126
Q

explain the action of alkalies ppt of monosaccharides

A

On treatment with dilute aqueous alkalies, both
aldoses and ketoses are changed to enediols. Enediol
is the enol form of sugar because two OH groups are
attached to the double bonded carbon. (Benedict and Fehlings test)

127
Q

explain the oxidation of monosaccharides i.e sugar acid

A

When aldoses oxidize under proper conditions they
may form:
– Aldonic acid
– Saccharic acids
– Uronic acid

128
Q

explain the reduction of monosaccharide ppt. (sugar alcohol)

A

Both aldoses and ketoses may be reduced by enzymes
or non-enzymatically to the corresponding polyhydroxy
alcohols.

129
Q

D-glucose becomes what sugar alcohol on reduction

A

D-sorbitol

130
Q

D-mannose becomes what sugar alcohol on reduction

A

D-mannitol

131
Q

D-fructose becomes what sugar alcohol on reduction

A

D-mannitol + D-sorbitol

132
Q

D-galactose becomes what sugar alcohol on reduction

A

D-dulcitol

133
Q

explain the Action of Phenylhydrazine (Osazone Formation) ppt of monosaccharides

A

Osazones are yellow or orange crystalline derivatives of
reducing sugars with phenylhydrazine and have a characteristic crystal structure, which can be used for
identification and characterization of different sugars
having closely similar properties (like maltose and lactose).

134
Q

explain how osazone formation would differentiate glucose, lactose and maltose

A

– Glucosazone are needle shaped
– Lactosazone are powder puff or tennis ball shaped
– Maltosazone are sunflower shaped.

135
Q

explain how glycosides are formed

A

Glycosides are formed when the hydroxyl group of anomeric carbon of a monosaccharide reacts with OH or NH group of second compound that may or may not be a carbohydrate. The bond so formed is known as glycosidic or glycosyl bond. The monosaccharides are joined by glycosidic bonds
to form disaccharides, oligosaccharides and
polysaccharides. In disaccharides, the glycosidic linkage may be either α or β depending on the configuration of the
atom attached to the anomeric carbon of the sugar

136
Q

Outline the therapeutic importance of glycosides

A

Glycosides are found in many drugs, e.g. in antibiotic streptomycin.
Cardiac glycosides such as Ouabain and digoxin increase heart muscle contraction and are used for treatment of congestive heart failure
Anthracycline glycosides (daunorubicin and doxirubicin), Daunorubicin is used to treat leukemia. Doxirubicin is used to treat a wide range of cancers.

137
Q

What are the derived sugars

A

Monosaccharides whose structure cannot be represented
by general formula or which have some unusual features

138
Q

List the derived sugars

A
  • Phosphoric acid ester of monosaccharides
  • Amino sugar
  • Deoxy sugars
  • Sugar acids
  • Sugar alcohols
  • Neuraminic acid
  • Sialic acid.
  • Glycosides
  • Furfural Derivative
139
Q

explain the formation of phosphoric acid ester of monosaccharides

A

These are formed from the reaction of phosphoric acid with hydroxyl group of the sugar, e.g. glucose-1-phosphate or glucose-6-phosphate.

140
Q

state the importance of the phosphoric ester of monosaccharides

A
  • Phosphorylation of sugar within cells is essential to prevent the diffusion of the sugar out of the cell.
  • Nucleic acids (RNA and DNA) of cell nuclei also contain sugar phosphates of ribose and deoxyribose
141
Q

explain the formation of amino sugars

A

Amino sugars have a hydroxyl group replaced by an amino or an acetylated amino (acetylamino) group. For example, glucosamine, N-acetyl glucosamine galactosamine and mannosamine.

142
Q

state the importance of the amino sugars

A
  • Amino sugars are components of glycolipid (ganglioside), glycoprotein and proteoglycans (glycosaminoglycans).
  • Several antibiotics, e.g. erythromycin, carbomycin contain amino sugar.
143
Q

explain the formation of deoxy sugar

A

Deoxy sugars possess a hydrogen atom in place of one of their hydroxy groups e.g. 2-deoxyribose found in nucleic acid DNA.

144
Q

what are the biochemical importance of deoxy sugars

A

Deoxyribose
* Oxygen is removed from 2nd position
* Is an important component of DNA
* Feulgen staining is specific for 2 deoxy sugars (and
DNA) in the tissues.
L–Fucose
* Deoxy Sugar present in the Blood group antigens.
2-Deoxy Glucose
* Experimentally an inhibitor of Glucose metabolism

145
Q

explain the formation of sugar acids

A

Formed by oxidation of aldehyde carbon atom, hydroxyl
carbon atom or both of monosaccharides.

146
Q

what are the importance of sugar acids

A
  • Ascorbic acid or vitamin C (not synthesized by
    human beings) is required for the synthesis of
    collagen. It acts as water soluble antioxidant.
  • Glucuronic acid (uronic acid) is a component of GAGs
147
Q

explain the formation of sugar alcohols

A

Monosaccharides are reduced at their carbonyl group
to yield corresponding polyhydroxyalcohols
* Aldoses undergo reduction to form corresponding
Alcohol
* Ketoses form two alcohols because of appearance of
new asymmetric carbon atom.

148
Q

what are the importance of sugar alcohols

A
  • Mannitol is used to reduce intracranial pressure by
    forced diuresis
  • Osmotic effect of Dulcitol and Sorbitol causes cataract
    in Galactosemia and Diabetes respectively
  • Polyol pathway is responsible for the development
    of Diabetic cataract.
  • they are used as non-glucose forming sweetners in food stuffs for diabetics, sorbitol and xylitol are the most commonly used.
149
Q

explain the formation of neuraminic acid

A

Neuraminic acid is a nine carbon sugar derived from
mannosamine (an epimer of glucosamine) and pyruvate.
Mannosamine + Pyruvate ————> Neuraminic acid.

150
Q

explain the formation of Sialic acid

A

Sialic acids are acetylated derivatives of neuraminic acid
in which amino (NH2) or hydroxy (OH) group is
acetylated.

151
Q

What is the importance of sialic acid

A

Sialic acids are constituents of both glycoproteins and glycolipids (ganglioside).

152
Q

what is isomerism

A

Different compounds having same molecular formula
are called isomers of one another.

153
Q

state lerbervont hoff rule of isomerism

A

Lebervon’t Hoff Rule: The relationship between the number of Asymmetric Carbon atom and the number of Stereoisomers possible. Number of isomers = 2 n
{where n is the number of Asymmetric Carbon atom.}

154
Q

what is the asymmetric carbon

A

The carbon atom to which four different substituent groups are attached is called a chiral or asymmetric carbon atom

155
Q

what are the types of isomerism in carbohydrates are

A
  • Stereoisomerism
  • Opticalisomerism.
156
Q

What is stereoisomerism

A

Compounds having the same molecular formula but
different spatial configuration of H and OH group around the asymmetric carbon atoms

157
Q

What are enantiomers

A

It is the difference in the orientation of H and OH group around
penultimate carbon atom results in two mirror images.
The penultimate carbon atom is called Reference Carbon atom (in Glucose and Fructose is C-5)

158
Q

Give examples of enantiomers

A

• D Glucose and L Glucose
• D Fructose and L Fructose
• D Mannose and L Mannose
• D Glyceraldehyde and L Glyceraldehyde.

159
Q

Comment on anomerism

A

• Formation of ring structure in monosaccharides
results in creation of an additional asymmetric carbon
called anomeric Carbon atom

• The carbon atom with functional group forms the
anomeric carbon atom

• In Glucose C-1 and in fructose C-2 form the anomeric
carbon atom

• Difference in orientation of H and OH group around
the anomeric carbon atom results in Anomerism

• The resulting isomers are called α and β anomers.

160
Q

Give examples of the anomers

A

• α D Glucose and β D Glucose
• α D Fructose and β D Fructose.

161
Q

Explain what mutarotation is

A

• Mutarotation is change in optical rotation of plane polarized light
with time
• Mutarotation is a property of Anomeric Carbon atom
• Mutarotation is studied by measuring the rotation of plane polarized
light
• The optical rotation of α D Glucose is + 112°
• The optical rotation of β D Glucose is + 19°
• Both undergo mutarotation over a period of a few hours, an
equilibrium is attained
• At equilibrium the optical rotation is + 52°.

162
Q

What is epimerism

A

When 2 monosaccharides differ from each other in
their configuration around a single asymmetric carbon
(other than anomeric carbon) atom, they are referred
to as epimers of each other.

163
Q

Give examples of epimers

A

Glucose has epimers at C2, C3, C4

C2- Mannose
C3- Allose
C4- Galactose

164
Q

Explain optical isomerism

A

• When a beam of plane polarized light is passed
through a solution of carbohydrates, it rotates the
light either to right or to left. Depends on the direction of rotation, 2 optical isomers possible
• Dextrorotatory (represented by d or +)
• Rotate plane polarized light to right (Clock-wise)
• Levorotatory (represented by l or –)
• Rotate plane polarized light to left (Anticlockwise)
• D Glucose is dextrorotatory (i.e. why glucose is also
called Dextrose) but D Fructose is levorotatory.

165
Q

What is a racemic mixture

A

Equimolar mixture of optical isomers which has no net rotation
of plane polarized light.

166
Q

Why is sucrose an invert sugar

A

Sucrose is dextrorotatory. On hydrolysis of Sucrose yield a mixture of dextrorotatory Glucose and levorotatory Fructose.
Because of strong levorotatory nature of fructose, Sucrose on hydrolysis is levorotatory. Hence, Sucrose is called invert
sugar

167
Q

what is a monosaccharide with no asymmetric carbon

A

dihydroxyacetone

168
Q

what osazones are Needle-shaped/Broomstick/Sheaves of Corn

A

Glucose, fructose, mannose

169
Q

what osazones are Pincushion with pins/Hedgehog/Flower of Touch-me-not

A

lactose

170
Q

what osazones are Sunflower Petal-shaped

A

maltose

171
Q

does sucrose form osazones

A

NO

172
Q

what are osazones

A

Osazones are yellow or orange crystalline derivatives of
reducing sugars with phenylhydrazine and have a characteristic crystal structure, which can be used for
identification and characterization of different sugars
having closely similar properties (like maltose and lactose).

173
Q

what are the principal sites of carbonhydrate digestion

A

mouth
stomach
intestine

174
Q

comment on the carbonhydrate digestion in the mouth

A
  1. In the mouth, salivary a-amylase cleaves starch by breaking a-1,4 linkages between glucose residues within the chains.
  2. Dextrins (linear and branched oligosaccharides) are the major products that enter the stomach.
175
Q

comment on the carbonhydrate digestion in the stomach

A

Carbohydrate digestion halts temporarily in the stomach
because the high acidity inactivates the salivary α-amylase.

176
Q

comment on the carbonhydrate digestion in the intestine

A
  1. The stomach contents pass into the intestine, where bicarbonate (HCO3) secreted by the pancreas neutralizes the stomach acid, raising the pH into the optimal range for the action of the intestinal enzymes. There are now 2 phases of intestinal digestion:
    -Digestion by pancreatic enzymes
    -Digestion by intestinal enzymes
177
Q

comment on carbonhydrate digestion by pancreatic enzymes

A

-The pancreas secretes an a-amylase that acts in the lumen of the small intestine and, like salivary amylase, cleaves a-1,4 linkages between glucose residues. The products of pancreatic a-amylase are:
- the disaccharides (maltose and isomaltase),
-trisaccharides, and
-small oligosaccharides containing a-1,4 and a-1,6 linkages.

178
Q

comment on carbonhydrate digestion by intestinal enzymes

A

Complexes of enzymes, produced by intestinal epithelial cells and located in their brush borders, continue the digestion of carbohydrates.
-Maltase breaks maltose into Glucose and Glucose
-Isomaltase breaks Isomaltose into Glucose and Glucose
-Lactase breaks lactose into Glucose and Galactose
-Sucrase breaks sucrose into glucose and fructose
-Dextrinase breaks Alpha-limit Dextrin into glucose and maltose

179
Q

comment on absorption of carbs

A

Carbohydrates are absorbed as monosaccharides from
the intestinal lumen. Two mechanisms are responsible
for the absorption of monosaccharides:
-Active transport
-Passive transport

180
Q

Comment on the active transport of carbs

A

It is transport against a concentration gradient, i.e. from a low glucose concentration to a higher concentration. The transport of glucose and galactose across the brush border membrane of mucosal cells occurs by an active transport.
A sodium dependent glucose transporter (SGLT-1) binds both glucose and Na+ at separate sites and transports them both through the plasma membrane of the intestinal cell

181
Q

comment on the facilitative transport of carbs

A
  • Fructose and mannose are transported across the brush border by a Na+ independent facilitative diffusion process, requiring specific glucose transporter, GLUT-5.
  • Movement of sugar in facilitative diffusion is strictly from a higher concentration to a lower one until it reaches an equilibrium.
  • The same transport can also be used by glucose and
    galactose if the concentration gradient is favourable.
182
Q

comment on the transport of glucose from the intestines to blood stream

A

The sodium independent transporter, GLUT-2 that facilitates transport of sugars out of the mucosal cells, thereby entering the portal circulation and being transported to the liver

183
Q

comment on lactose intolerance

A

This is the most common disorder due to deficiency of enzyme lactase.
* In this condition, lactose accumulates in the gut which undergoes bacterial fermentation in the large intestine with the production of H2 and CO2 gases and low molecular weight acids like acetic acid, propionic acid and butyric acid which are osmotically active.

  • Abdominal cramps and flatulence result from the accumulation of gases and the osmotically active products that draw water from the intestinal cells into the lumen resulting in diarrhoea and dehydration.
  • Treatment for this disorder is simply to remove lactose from the diet.

MB prep: Biochemistry. (15 decks)

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