Carbohydrates

• Carbohydrate Types

  A) Polysaccharides

  B) Monosaccharides

  C) Disaccharides

  D) Sucrose

  E) Lactose

  F) Maltose

  G) Cellulose

  H) Starch

  I) Glycogen

  J) Hexose

  K) Penose

  L) Triose

  M) Glucose

  N) Fructose

  O) Galactose

  P) Deoxyribose

  Q) Ribose

  R) Glyceraldehyde

  
• Stereoisomers Diagram:

  A) alpha glucose

  B) beta glucose

  
• Stereoisomers Diagram:

  A) CH_2OH

  B) CH_2OH

  C) O

  D) O

  E) H

  F) H

  G) OH

  H) OH

  I) H

  J) OH

  K) H

  L) H

  M) H

  N) OH

  O) H

  P) OH

  Q) OH

  R) H

  S) H

  T) OH

  U) H

  V) H

  
• Key carbohydrate information

  • “Carb” - carbon, “hydr” - hydrogen, “ates” - oxygen
  • Hydrogen to oxygen ratio is same as water (2:1)
  • Carbohydrates are hydrated carbons; general formula is CH_2O
  • Three main groups:
  • Monosaccharides (Single sugars, monomers)
  • Disaccharides (Double sugars, bond of two monosaccharides)
  • Polysaccharides (Polymers of monosaccharides)
• Describe physical properties of key carbohydrates

  Mono- and disaccharides:

  • Small molecules
  • Simple sugars
  • water-soluble (polar; -OH groups)
  • Crystalline
  • Taste sweet (e.g. sugar)

  Polysaccharides:

  • Macromolecules (large)
  • Polymers
  • Insoluble in water
  • Do not taste sweet (e.g. flour)
• Glucose


  • Hexose sugar; six-membered structure
  • Formula: C_6H_12O_6
  • To count carbon, find oxygen, then count going clockwise
  • OH is hydroxyl group
  • In ring structure and straight form in solution, equilibrium between them, but ring is predominant
• Glucose Diagram

  Label

  A) CH_2OH

  B) O

  C) H

  D) OH

  E) OH

  F) H

  G) H

  H) OH

  I) OH

  J) H

  K) H

  
• Monosaccharide


  • Monomers of single sugar unit
  • General formula is (CH_2O)n
  • Sub-grouped according to their carbon atoms
  • Suffix-ose is used in naming, mostly
  • -OH group is a hydroxyl group (polar, reason for water-solubility)
  • In straight-chain form, all but 1 C has attached -OH; other has carbonyl group (C=O); ketone or aldehyde, makes them reducing sugars
  • Benedict’s test: Reducing sugars give positive test; reduce copper (II) sulphate to copper (I), change from blue to brick red, green, or orange-brown (depends on sugar concentration)
• Monosaccharide types


  Hexose:

  • 6 carbon sugar
  • General Formula: C_6H_12O_6
  • Glucose (for respiration)
  • Fructose (in nectar, sweetness attracts pollinators)
  • Galactose (With glucose, fors lactose, energy source for young animals)

  Pentose:

  • 5 carbon sugar
  • General Formula: C_5H_10O_5
  • Ribose (In RNA + ATP)
  • Deoxyribose (In DNA)

  Triose:

  • 3 carbon sugar
  • General Formula: C_3H_6O_3
• Isomers


  • Many chemical bonds in glucose release energy when hydrolysed in respiration (for ATP)
  • Plants and animals respire alpha glucose, not beta glucose
  • Structural Isomers:
  • Slightly different properties
  • Monosaccharides have same molecular formula but varied structural formulae
  • Stereoisomers:
  • Glucose has two; vary slightly structurally (α-glucose and β-glucose) and have different properties
• Disaccharides


  • 2 monosaccharides bond (by condensation reaction); forms disaccharide and water molecule
  • Bond between reacting monosaccharides is glycosidic
  • General formula: 2(CH_2O)n - H_2O
  • Can be hydrolysed into monosaccharide monomers by adding water
  • Maltose and lactose are both reducing, Sucrose is not (carbonyl group lost in glycosidic bond formation)
  • Gives negative reaction to Benedict's
  • Test for non-reducing sugars
  • Boil with dilute hydrochloric acid to hydrolyse sugar to constituent monosaccharides
  • Neutralise by mixing with sodium hydroxide
  • Retest with Benedict's
• Disaccharide types


  Maltose:

  • From 2 α-glucose molecule (between carbons 1 and 4; α 1-4 glycosidic bond)
  • Glucose (energy) source in germinating seeds (formed in starch breakdown in seed food store)

  Sucrose

  • Glucose + Fructose
  • Form sugars transported in green plants (in phloem)

  Lactose:

  • Glucose + Galactose
  • Milk Sugar, energy source for young mammals
• Polysaccharide


  • Formed when many monosaccharide monomers bond together by condensation
  • Form long chains/polymers; large macromolecules
  • Key Examples: Starch, Cellulose, Chitin, Glycoen, Callose