MONOSACCHARIDES

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MONOSACCHARIDES

• DR AMINA TARIQ
• BIOCHEMISTRY

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Carbons Category Name Relevant examples
3 Triose Glyceraldehyde, Dihydroxyacetone
4 Tetrose Erythrose
5 Pentose Ribose, Ribulose, Xylulose
6 Hexose Glucose, Galactose, Mannose, Fructose
7 Heptose Sedoheptulose
9 Nonose Neuraminic acid, also called sialic acid
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• Three common sugars share the same molecular
  formula C6H12O6. Because of their six carbon
  atoms, each is a hexose.

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• They are
• glucose, "blood sugar", the immediate source of
  energy for cellular respiration
• galactose, a sugar in milk (and yogurt), and
• fructose, a sugar found in honey.

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• The simplest monosaccharides of biological
  interest have n3 (trioses)
• Glyceraldehyde and Dihydroxyacetone

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• GLYCERALDEHYDE
• It is the smallest sugar
• It has got three carbons
• Its carbon 2 is asymmetric carbon
• All monosaccharides having more than 3 carbons
  will have two or more asymmetric carbon atoms.
• For D and L designation all monosaccharides are
  compared with glyceraldehyde.
• Thus it is called a reference sugar.

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• For sugars with more than one chiral center, D
  or L refers to the asymmetric C farthest from the
  aldehyde or keto group.

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• DIHYDROXYACETONE
• It is the only exception of a monosaccharide that
  does not possess any asymmetric carbon.

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MONOSACCHARIDES

• Monosaccharides are carbohydrates that cannot be
  hydrolyzed to obtain smaller molecules of
  carbohydrate.
• White crystalline solids , very soluble in water,
  have sweet taste.

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Glucose

• Glucose is by far the most common carbohydrate
  and classified as a monosaccharide,
• an aldose,
• a hexose,
• and is a reducing sugar.
• Principal MS utilized for energy purposes.

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• It is also known as dextrose, because it is
  dextrorotatory.
• Glucose units combine and give rise to
• Glycogen
• Starch
• Cellulose

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• Glucose is also called blood sugar as it
  circulates in the blood at a concentration of
  65-110 mg/mL of blood.
• Normally trace amounts in urine
• Increased amounts in diabetes mellitus.

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• Glucose is initially synthesized by chlorophyll
  in plants using carbon dioxide from the air and
  sunlight as an energy source. Glucose is further
  converted to starch for storage.

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• an aqueous sugar solution contains only 0.02 of
  the glucose in the chain form, the majority of
  the structure is in the cyclic chair form.

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Fructose

• Fructose is classified as a
• monosaccharide,
• the most important ketose sugar,
• a hexose,
• and is a reducing sugar.
• Fructose, along with glucose are the
  monosaccharides found in disaccharide, sucrose.
• Sweetest of all sugars.

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• Fruit juices. Honey.
• Hydrolysis of cane sugar and of inulin.
• Can be changed to glucose in the liver and so
  used in the body.
• Main source of energy for the spermatozoa
• Levorotatory (in sucrose dextrorotatory)
• Hereditary fructose intolerance

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Galactose

• Galactose is classified as a
• monosaccharide,
• an aldose,
• a hexose,
• and is a reducing sugar.

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• Hydrolysis of lactose
• Galactose is more commonly found in the
  disaccharide, lactose or milk sugar.
• It is found as the monosaccharide in peas.
• Constituent of glycolipids and glycoproteins.
• C-4 epimer of glucose
• Galactose is part of nerve and brain
  biochemicals, so milk is essential to infants.

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Pentoses

• Xylulose- uronic acid pathway
• Arabinose and xylose- glycoproteins
• Ribose - RNA
• Deoxyribose - DNA

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• All are classified as
• monosaccharides,
• aldoses,
• Pentoses,
• and are reducing sugars.

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Ribose

• Ribose and its related compound, deoxyribose,
  are the building blocks of the backbone chains in
  nucleic acids, better known as DNA and RNA.
• Ribose is used in RNA and deoxyribose is used in
  DNA.

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• The presence or absence of the -OH group on
  carbon (2) is an important distinction between
  ribose and deoxyribose.
• Ribose has an alcohol at carbon 2, while
  deoxyribose does not have the alcohol group.
• Deoxy hexoses also present in milk and blood
  group substances.

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Disaccharides

• Three common disaccharides
• Sucrose common table sugar glucose fructose
• Lactose major sugar in milk glucose
  galactose
• Maltose product of starch digestion glucose
  glucose

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• The resulting linkage between the sugars is
  called a glycosidic bond. The molecular formula
  of each of these disaccharides isC12H22O11 2
  C6H12O6 - H2O

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Sucrose

• Sucrose is made from glucose and fructose units
• Sucrose or table sugar
• Cane, beet sugar, Pineapple
• Has no free anomeric carbon
• Is a non-reducing sugar

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• Dextrorotatory
• Invert sugar
• No osazone crystals
• In sucrase deficiency, malabsorption leads to
  diarrhea and flatulence

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Lactose

• Glucose Galactose
• Milk sugar
• May occur in urine during pregnancy
• In lactase deficiency, malabsorption leads to
  diarrhea and flatulence
• Certain bacteria can ferment lactose to lactic
  acid - souring of milk. ( lactobacillus)

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Maltose

• Glucose Glucose
• Digestion by amylase or hydrolysis of starch.
• Reducing sugar
• Baby and invalid foods

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• LACTULOSE -
• galactose and fructose
• Osmolar laxative
• Relieves Constipation