This document provides an overview of carbohydrate structure and metabolism. It defines carbohydrates and discusses their classification as monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Key monosaccharides like glucose, fructose and galactose are described. The document also covers carbohydrate isomerism, glycosidic linkages in disaccharides and polysaccharides, and structural features of important polysaccharides like starch, glycogen and cellulose. Carbohydrate metabolism and roles in the body are also summarized.

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2.  Definition,
 Biological importance and classification.
 Monosaccharides : Isomerism, anomerism.
 Sugar derivatives,
 Disaccharides.
 Polysaccharides.
 Structure of starch and glycogen
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3.  Mostly derived from plant.
 Animals - synthesize carbohydrate from lipid
glycerol and amino acids.
 Glucose - major metabolic fuel of mammals
and a universal fuel of the fetus.
 Other sugars are converted into glucose in the
liver.
• Diabetes mellitus, galactosemia,
glycogen storage diseases, and lactose
intolerance are some of the disease
related to carbohydrate metabolism
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4.  Dietary source of energy.
 Form the structural framework of RNA and DNA.
 Structure of cell membrane and cell wall of plant
cell & microorganism and exoskeleton of insects
 Precursor for synthesis of all the other
carbohydrates in the body,
◦ glycogen for storage.
◦ ribose and deoxyribose in nucleic acids.
◦ Galactose - lactose of milk, in glycolipids.
◦ Combination with protein - glycoproteins and
proteoglycans
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5.  They are oxidised polyhydroxy alcohols,
having the general formul (CH2O)n where n =
number of carbon atom.
 Glycerol can be considered as the parent
compound, although its not a carbohydrate.
 It can be further oxidised to get
◦ Aldehyde (glyceraldhehyde)
◦ Ketone (dihydroxyacetone).
• This 2 forms the basis of all the
carbohydrates
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6.  Important characteristics of
monosaccharide.
 Same structural formulae but
differs in their spatial
arrangement.
 A carbon is said to
assymetric or chiral when its
is attached to different
atoms or groups.
 Possible number of isomers
– 2n where n = number of
chiral carbon atoms.
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7.  Arrangement of – OH
and –H : adjacent to
the terminal alcohol
determines the
isomerism
 D- isomer has –OH on
its right and L-isomer
has –OH on its left.
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8.  Optical activity is characteristic principle of
asymetric carbon atom.
 Polarized light when passed through solution
◦ turns to left – Levorotatory (-)
◦ and if it turns to right – Dextrorotatory (+).
• So carbohydrate can be either D(+),
D(-), L(+), L(-).
• Racemic mixture : when D and L
isomers are present in equal
concentration which doesn’t shows
any optical activity.
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10.  Isomers differing as a result of variations in
configuration of the -OH and -H on carbon atoms
other than functional group or last carbon are known
as epimers.
 Ex: epimers of glucose
◦ Mannose epimer at 2nd carbon
◦ Galactose epimer at 4th carbon
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11.  Chiral molecules that are
mirror images of one
another.
 molecules are non-
superimposable on one
another
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12.  Aldehyde reacts with
alcohol to give hemiacetal
 Ketone reacts with alcohol
to form hemiketal.
 Hydroxyl group of sugar
molecule can react with its
own aldehyde/ketone.
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13.  Aldehyde group of
glucose at C1 reacts
with alcohol at C5 – ß
& α cyclic hemiacetals.
 This can be represented
either by Fischer
formulae or Haworth
projection formulae.
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14.  Anomers are the cyclic
isomers differing from
each other in
configuration at
anomeric carbon i.e at
C1. Ex: α and ß form.
 Both this anomers of D-
glucose interconvert in
aqueous solution by a
process called
mutarotation
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15.  Anomers of D-glucose interconvert in
aqueous solution by a process called
mutarotation.
 Solution of α-D-glucose and a solution of β-
D-glucose - form identical equilibrium
mixtures having identical optical properties.
◦ one-third α -D-glucose
◦ two-thirds β-D-glucose,
◦ very small amounts of the linear and five –
membered ring (glucofuranose) forms
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16.  Pyranoses : 6-membered
ring compounds - resemble
the 6-membered ring
compound pyran.
 Furanoses : cyclic forms
having 5 membered rings -
resemble the 5 membered
ring compound furan.
 Aldopyranose ring is much
more stable than the
aldofuranose ring
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17.  Aldehyde or ketone derivatives of polyhydric
alcohol.
 They are mainly classified as
◦ Monosaccharides
◦ Disaccharides
◦ Oligosaccharide
◦ Polysaccharides
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18.  Cannot be hydrolyzed into simpler
carbohydrates.
 Aldoses or ketoses depending
upon whether they have an
aldehyde or ketone group.
 Based on the number of carbon
atoms, monosaccharide are
classified as trioses, tetroses,
pentoses, hexoses and heptoses
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19.  colorless, crystalline
solids
 freely soluble in water
but insoluble in
nonpolar solvents
 Most have a sweet
taste
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20.  Aldopentose
◦ D-ribose - component of RNA and of nucleotide
coenzyme
◦ D-xylose and L-arabinose - constituents of
polysaccharides in the walls of plant cells
 Aldohexoses
◦ D-glucose – huge proportion of the biomass is accounted
for by glucose polymers, cellulose and starch
◦ Free D-glucose : plant juices (grape sugar) and as
blood sugar
◦ D - galactose - constituent of lactose (milk sugar)
 Together with D-mannose, galactose is also found in
glycolipids and glycoproteins
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22.  Ketopentose
◦ D-ribulose : intermediates
in the pentose phosphate
pathway and photosynthesis
◦ D-fructose: most widely
distributed, fruit juices and
in honey, sucrose and inulin
(bound sucrose)
 Deoxyaldoses
(deoxyribose)
◦ OH group is replaced by a
hydrogen atom from ribose
sugar
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23.  Condensation products of two to ten
monosaccharides.
 Based on this number this are further
subdivided into
◦ Disaccharide
◦ Trisaccharide etc
 Ex: maltotriose.
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24.  consists of two sugars joined by an
O-glycosidic bond
 Ex: maltose, sucrose and lactose.
 Sucrose
◦ anomeric carbon atoms of a glucose
unit and a fructose unit are joined
◦ glycosidic linkage is α for glucose and
β for fructose
• Lactose
 disaccharide of milk
 consists of galactose joined to glucose by a
β-1,4-glycosidic linkage
 Turns to monosaccharides by lactase in
human beings
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25.  Maltose
◦ two glucose units - joined by
an α -1,4 glycosidic linkage
◦ hydrolysis of starch and is in
turn hydrolyzed to glucose by
maltase
 In humans this are located
on the outer surfaces of
epithelial cells lining the
small intestine
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26.  condensation products of more than ten
monosaccharide units.
 Linear or branched polymers
 Usually tasteless and forms colloids with wates
 Its again further subdivided into –
homopolysachharides and
heteropolysaccharides.
 Ex: starches and dextrins
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27.  homopolymer of glucose
forming an α- glucosidic
chain
 abundant dietary
carbohydrate in cereals,
potatoes, legumes, and other
vegetables
 two main constituents
◦ Amylose (15–20%) : non-
branching helical structure
◦ Amylopectin (80–85%) :
branched chains composed of
24–30 glucose residues united
 by 1 → 4 linkages in the chains
 by 1 → 6 linkages at the
branch points
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28.  storage polysaccharide in
animals.
 Glucose gets converted to
glycogen by a process
called glycogenesis
 more highly branched
structure than amylopectin
 chains of 1–4 α-D-
glucopyranose residues
 With branching by means
of α(1 → 6)-glucosidic
bonds
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29.  polysaccharide of fructose
 found in tubers and roots of
dahlias, artichokes and
dandelions
 readily soluble in water and
is used to determine the
glomerular filtration rate
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30.  Dextrins : intermediates in the hydrolysis of
starch
 Cellulose
◦ insoluble and consists of β-D-glucopyranose
units
◦ linked by β(1 → 4) bonds to form long, straight
chains strengthened by cross-linked hydrogen
bonds
◦ source of “bulk” in the diet
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31.  Chitin
◦ structural polysaccharide in
the exoskeleton
of crustaceans and insects
and also in mushrooms
◦ N-acetyl-D-glucosamine
units joined by
β (1 → 4)-glycosidic
linkages
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32.  Mucopolysaccharides
 complex carbohydrates characterized by their content
of amino sugars and uronic acids.
 Proteoglycan : when GAG chains are attached to a
protein molecule.
 ground or packing substance of connective tissues
◦ holding large quantities of water - lubricating
◦ occupying space – cushioning
◦ large number of OH groups and negative charges on the
molecules,
◦ keep the carbohydrate chains apart
• Ex: hyaluronic acid, chondroitin sulfate, and heparin
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34.  Mucoproteins
 different situations in fluids and tissues,
including the cell membranes
 containing branched or unbranched
oligosaccharide chains
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35.  Color_Atlas_of_Biochemistry_2005
 Harpers_Biochemistry_26th_ed
 Lehninger Principles of Biochemistry, Fourth
Edition - David L. Nelson, Michael M. Cox.
 Biochemistry – U. Satyanarayan, U.
Chakerpeni
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