This document discusses monosaccharides, which are the simplest forms of carbohydrates. It defines monosaccharides as polyhydroxy aldehydes or ketones that cannot be further broken down by hydrolysis. The document outlines the key properties and classifications of monosaccharides, including that they are reducing sugars, contain asymmetric carbons, and often exist as cyclic structures called pyranoses and furanoses. Examples of important monosaccharides are glucose, galactose, and fructose. Glucose is a critical energy source, while mannose and derivatives have biological roles.

1. MONOSACCHARIDES
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Presented by:
Adeel Akram
Iqra Saeed
Saqiba Koukab
Masood Ahmad

2. Carbohydrates
• Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield such compounds
on hydrolysis.
• Carbohydrates are the most abundant biomolecules on Earth.
• Many, but not all, carbohydrates have the empirical formula (CH₂O)n.
• some also contain nitrogen, phosphorus, or sulphur.
• oxidation of carbohydrates is the central energy-yielding pathway in most non-photosynthetic cells.
• Carbohydrate polymers (also called glycan's) serve as structural and protective elements in
the cell walls of bacteria and plants and in the connective tissues of animals e.g.(Chitin, Cellulose)
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3. 18/01/2020 3
Fig1: Shows the nitrogen containing
carbohydrates
Fig2: Shows the phosphorous containing
carbohydrates
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4. • carbohydrate polymers lubricate skeletal joints and participate in recognition and adhesion between
cells.
• Complex carbohydrates covalently linked with other chemical species such as proteins, peptides,
lipids and saccharides. called glycoconjugates.
• There are three major classes of carbohydrates are
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Carbohydrates
Monosaccharides oligosaccharides Polysaccharides
Fig3:Shows the glycoconjugates
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5. Monosaccharides
• Monosaccharides are simplest of the carbohydrates the monosaccharides are either aldehydes or
ketones with two or more hydroxyl group.
• The six-carbon monosaccharides glucose and fructose have five hydroxyl groups.
• These sugars further cannot be hydrolyzed into simple sugars.
• General formula of monosaccharides is Cn (H₂O)n where n has value from 3 to 7 e.g. in glucose
n = 6 so chemical formula of glucose is C₆H₁₂O₆.
• If they contain aldehyde group known as aldo-sugar or ketone group known as keto-sugar.
• They are sweet in taste.
• They are readily soluble in water.
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6. Monosaccharides Are Aldoses and Ketoses
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• If the carbonyl group is at an end of the carbon chain the monosaccharide is an aldose.
• if the carbonyl group is at any other position(in a ketone group)the monosaccharide is a ketose.
• The simplest monosaccharides are the two three-carbon trioses glyceraldehyde, an aldotriose
and dihydroxyacetone a ketotriose.
Fig4: Shows the Two trioses an aldose and a ketose. The carbonyl group in each is shaded.M.ADEEL AKRAM

7. Monosaccharides have asymmetric centers
• All the monosaccharides accept dihydroxyacetone contain one or more asymmetrical chiral carbon.
• So they are optically active isomeric form.
• The simplest aldose glyceraldehyde contains one chiral center.
• Therefore has two different optical isomers or enantiomers.
• Enantiomers: Stereoisomers that are nonsuperposable mirror images of each other.
• Usually a molecule with n chiral centers can have 2n stereoisomers. Glyceraldehyde has 21 = 2
similarly hexoses having 4 chiral center so 44 = 16 stereoisomers.
18/01/2020 7Fig5: Shows the enantiomers of glyceraldehydeM.ADEEL AKRAM

8. • Two sugars which are differ only in the configuration of around one carbon atoms are called as
epimers.
• D-glucose and D-mannose are differ at the C-2 are epimers.
• Similarly D-glucose and D-galactose are differ only at C-4.
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9. D&L Stereoisomers
• All of the monosaccharides except dihydroxyacetone contain one or more asymmetric
(chiral) carbon atoms.
• The simplest aldose glyceraldehyde contains one chiral center (the middle carbon atom)
and therefore has two different optical isomers.
• when the hydroxyl group on the reference bottom chiral carbon is on the right (dextro)
the sugar is the D isomer. when on the left (levo) it is the L isomer.
• There are 16 possible aldohexoses out of them eight are D forms and eight are L.
• Most of the hexoses of living organisms are D isomers.
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10. Structures of the D-Aldoses
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11. Structure of D-ketose
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12. Formation of Hemiacetals and Hemiketals
• Aldotetroses and all monosaccharides with five or more carbon atoms occur predominantly as
cyclic ring structures in which the carbonyl group has formed a covalent bond with the oxygen of a
hydroxyl group along the chain.
• The formation of these ring structures is the result of a general reaction between alcohols and
aldehydes or ketones to form derivatives called hemiacetals or Hemiketals.
• Actually, two molecules of an alcohol can add to a carbonyl carbon. The product of the first
reaction for an aldose is a hemiacetal while the product of the first reaction for a ketose is a
hemiketal.
• The addition of the second alcohol molecule produces the full acetal or ketal, and the bond formed
is a glycosidic linkage.
• When the two reacting molecules are both monosaccharides, the acetal or ketal produced is a
disaccharide.
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Fig: Shows the formation of acetal & ketal
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13. Cyclization of D-Glucose
• The reaction of the first alcohol with an aldose or ketose creates an additional chiral center at
which was the carbonyl carbon.
• Because the alcohol can add to the carbonyl carbon by attacking either from the “front” or the
“back” the reaction can produce either of two stereoisomeric configurations denoted  and β.
• For example, D-glucose exists in solution as an intermediate hemiacetal in which the free hydroxyl
group at C-5 has reacted with the aldehyde C-1 latter carbon asymmetric and producing two
possible stereoisomers designated  and β .
• These two isomeric forms, which differ only in their configuration about the hemiacetal carbon
atom are called anomers and the carbonyl carbon is called the anomeric carbon.
18/01/2020 13Fig: Shows the cyclization of glucoseM.ADEEL AKRAM

14. Pyranoses and Furanoses
• Six carbon(aldehyde) monosaccharide ring compounds are called pyranoses
because they resemble pyran.
• Ketohexoses (such as fructose) also occur as cyclic compounds with  and
β anomeric forms. In these compounds the hydroxyl group at C-5 (or C-6) reacts
with the keto group at C-2, forming a furanoses because they resemble furan.
• The systematic names for the two ring forms of D-glucose are therefore
-D-glucopyranose and β-D-glucopyranose.
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Fig: Shows the glucopyranoses
fructofuranoses
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15. Reducing and non-reducing sugar
• A reducing sugar is any sugar that is capable of acting as a reducing agent because it has a free
aldehyde group or a free ketone group.
• All monosaccharides are reducing sugars, along with some disaccharides, oligosaccharides, and
polysaccharides.
• A non-reducing sugar is a carbohydrates that is not oxidized by a weak oxidizing agent.
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Fig: Shows the reducing sugar Fig: Shows the non-reducing sugars
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16. Fisher and Howarth projection
• The Fischer projection, devised by Emil Fischer in 1891, is a two-dimensional representation of a
three-dimensional organic molecule by projection.
• A Haworth projection is a common way of writing a structural formula to represent the
cyclic structure of monosaccharides with a simple three-dimensional perspective.
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Fig: Shows the Fischer & Haworth projection
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17. Mutarotation
• “Muta” means change so its means a change in rotation.
• It refers to the change in specific rotation over time due to change between isomers.
• Cyclic sugars shows the mutarotation as α and β anomeric forms interconvert.
• When an aldohexoses is first dissolved in water and the solution is put in optical path so that plane
polarized light is passed, rotation showed by the sugar gradually.
• This phenomenon of change of rotation is called as mutarotation.
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18. Derivatives of monosaccharides
• Sugars having derivatives such as glucose, galactose and mannose there are a number of sugar
derivatives in which a hydroxyl group in the parent compound is replaced with another substituent.
• In glucosamine,galactosamine and mannosamine, the hydroxyl at C-2 of the parent compound is
replace with an amino group.
• The amino group is nearly always condensed with acetic acid, as in N-acetylglucosamine. This
glucosamine derivative is part of many structural polymers, including those of the bacterial cell
wall.
• Oxidation of the carbonyl (aldehyde) carbon of glucose to the carboxyl level produces gluconic
acid.
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19. 18/01/2020 19Fig: some important hexose derivatives important in biologyM.ADEEL AKRAM

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21. Importance of monosaccharides
• The hexoses glucose, galactose and fructose are important monosaccharides.
• Glucose is the most prevalent monosaccharide in diet.
• Glucose is one of the primary molecules which serve as energy sources for plants and animals.
• In the presence of oxygen, glucose breaks down into carbon dioxide and water, and energy is
released as a by product.
• D-glucose also known as dextrose and blood sugar, is found in fruits, vegetables, corn syrup, and
honey.
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22. • D-mannose is used to treat a rare disease(CDGS) called carbohydrate-deficient glycoprotein
syndrome type 1b.
• After the age of 15 the disease was mainly characterised by neurological symptoms consisting of
non-progressive ataxia & mental retardation.
• It may also reduce low blood sugar in people with this disease.
• D-mannose may also treat or prevent urinary tract infections (UTIs).
• The typical dose of D-mannose for UTI treatment is 500 mg, in capsule or powder form, taken in
a glass of water or juice every two to three hours for five days.
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