Carbohydrate Chemistry Quiz

Carbohydrate Chemistry

• Carbohydrates are polyhydroxy alcohols with functional aldehyde or ketol groups.
• The ratio between Carbon and H2O in carbohydrates is usually 1:1.
• Carbohydrates are classified based on the products formed during hydrolysis.

Monosaccharides

• General Formula: C_n(H₂O)_n
• Classification:
  • Number of Carbon Atoms:
    • Trioses (3 carbons): Aldotrioses and Ketotrioses
    • Tetroses (4 carbons): Aldotetroses and Ketotetoses
    • Pentoses (5 carbons): Aldopentoses and Ketopentoses
    • Hexoses (6 carbons): Aldohexoses and Ketohexoses
    • Heptoses (7 carbons): Ketoheptoses
  • Functional Group:
    • Aldoses: Contain an aldehyde group.
    • Ketoses: Contain a ketone group.

Aldoses

• Parent Aldose: Glyceraldehyde.
• Glyceraldehyde Structure:
  • 1st Carbon: Aldehyde group (H-C=O)
  • 2nd Carbon: Secondary alcohol group (H-C-OH)
  • 3rd Carbon: Primary alcohol group (CH₂OH)
• D and L Forms: Glyceraldehyde exists in D or L forms.
• Higher Aldoses: Formed by inserting a secondary alcohol group below the aldehyde group.

Asymmetric Carbon Atoms

• A carbon atom attached to four different atoms or groups.

Isomers

• Optical Isomers: Compounds with the same molecular formula but different orientations of H or OH around one or more asymmetric carbons.
  • Epimers: Optical isomers with more than one asymmetric carbon, where all are the same except for one.
    • Glucose and Mannose: Epimers at C2.
    • Glucose and Galactose: Epimers at C4.
  • Anomers: Optical isomers representing the α and β forms of a sugar in its ring structure.
    • α, D-glucopyranose and β, D-glucopyranose.
  • Enantiomers: The D and L forms of a sugar; they are mirror images.
    • D-glyceraldehyde and L-glyceraldehyde.
    • D-glucose and L-glucose.
• Aldose-Ketose Isomers: Isomers with the same molecular formula but different functional groups.
  • Example:
    • Trioses: Glyceraldehyde (aldose) and Dihydroxyacetone (ketose)
    • Tetroses: Erythrose (aldose) and Erythrulose (ketose)
    • Pentoses: Ribose and Xylose (aldoses) and Ribulose and Xylulose (ketoses)
    • Hexoses: Glucose, Galactose, and Mannose (aldoses) and Fructose (ketose)

Ring Structure of Monosaccharides

• Pentoses and Hexoses can exist in cyclic forms.
• The cyclic form is due to a reaction between the carbonyl group (C=O) of the aldehyde or ketone with an alcoholic hydroxyl group.
  • Furanose: 4-carbon ring.
  • Pyranose: 5-carbon ring.
• Haworth Formula: Describes the cyclic structure.
  • Groups on the left side in the straight formula are written upwards.
  • Groups on the right side in the straight formula are written downwards.
• Anomeric Carbon:
  • The first carbon in the cyclic structure becomes an asymmetric carbon.
  • α Form: OH group is on the right side of the anomeric carbon.
  • β Form: OH group is on the left side of the anomeric carbon.

Polysaccharides

• Polymers of monosaccharides.
• Classified based on the type of monosaccharide units present.

Homopolysaccharides

• Contain only one type of monosaccharide.
• Examples:
  • Glucans: Formed of D-glucose units.
    • Starch
    • Glycogen
    • Cellulose
  • Fructans:
    • Inulin: Formed of D-fructose units, found in plants, used to assess renal functions.

Glucans

• Starch:
  • Storage form of carbohydrate in plants.
  • Sources: Cereals, legumes, and tubers.
  • Types:
    • Amylose (15%):
      • Linear polymer of glucose units linked by α1-4 glycosidic bonds.
      • Found in the inner part of starch granules.
      • Hydrolyzed by α-amylase to maltose, then to D-glucose.
    • Amylopectin (85%):
      • Branched polymer of glucose units with α1-4 glycosidic bonds and α1-6 glycosidic bonds at branching points.
      • Found in the outer part of starch granules.
      • Hydrolyzed by α-amylase to maltose and isomaltose, then to D-glucose.
• Glycogen (Animal Starch):
  • Storage form of carbohydrate in animals.
  • Found in the liver and muscles.
  • More branched than amylopectin and has a higher molecular weight.
  • Hydrolyzed by α-amylase to maltose and isomaltose, then to D-glucose.
• Cellulose:
  • Linear polymer of β, D-glucose units linked by β1-4 glycosidic bonds.
  • Found in plants, vegetables, and cotton.
  • Insoluble in water.
  • Not digested by humans because the β1-4 glycosidic linkage is not cleaved by amylase.
  • Important for dietary fiber and preventing constipation.

Heteropolysaccharides

• Contain more than one type of monosaccharide.
• Examples:
  • Glycosaminoglycans (GAGs) or Mucopolysaccharides
  • Proteoglycans

Glycosaminoglycans (GAGs)

• Long, unbranched heteropolysaccharides.
• Composed of uronic acid and amino sugar units.
• Classification:
  • Sulfate Free GAGs:
    • Hyaluronic acid
  • Sulfate Containing GAGs:
    • Chondroitin sulfate
    • Dermatan sulfate
    • Keratan sulfate
    • Heparin
    • Heparan sulfate

Proteoglycans

• GAGs covalently linked to a protein core.
• Structure: 95% carbohydrates and 5% proteins.
• Site: Extracellular matrix, ground substance in association with extracellular proteins.
• Functions of GAGs and Proteoglycans:
  • Components of the extracellular matrix.
  • Attract water, forming hydrated gels.
  • Act as lubricants in synovial fluid.
  • Play roles in cell signaling and immune responses.