Carbohydrates

• Carbohydrates consist of elements Carbon, Hydrogen and Oxygen.
• Monosaccharides- simple sugars like glucose, fructose and ribose.
• A single sugar unit (monomer) is able to join together to form disaccharides (double sugars) and polysaccharides (polymers). General formula (CH2O)n where n can be any number from 3 to 7. 
• Monosaccharides have 3 similar properties:

  • Soluble in water
  • Sweet tasting
  • Form crystals
• Alpha glucose (α glucose) is easily transported (water soluble) and readily used in respiration. The OH groups on C1 and C4 are below the carbon.  
• Beta glucose – (β glucose) is found in cellulose and has the same molecular formula C6H12O6   however the OH group on C1 is above the Carbon and below on C4.  
• Alpha Glucose

  A) CH2OH

  B) H

  C) OH

  D) O

  E) H

  F) H

  G) OH

  H) OH

  I) H

  J) H

  K) HO

  
• Two monosaccharide sugars can join together to form a disaccharide. This reaction is known as a condensation reaction, as a water molecule is removed and a covalent bond called a glycosidic bond is formed.
• The molecular formula for disaccharides is C12H22O11.
• Maltose is a disaccharide formed by a condensation reaction between two glucose molecules  
• Sucrose is a disaccharide formed by a condensation reaction between a glucose and fructose molecule. 
• Lactose is a disaccharide formed by a condensation reaction between a glucose and galactose molecule
• Polysaccharides are polymers formed by combining many monosaccharide molecules together by glycosidic bonds formed during condensation reactions.  
• Starch is a coiled, compact polysaccharide made from two polymers amylose and amylopectin and forms the main storage carbohydrate in plants. 
• Characteristics of Starch:

  • Large polysaccharide joined by glycosidic bonds formed by condensation reactions between alpha glucose monomers.
• Characteristics of starch:

  • Insoluble therefore does not affect the water potential of the cell, so water does not move into the cell by osmosis 
• Characteristics of starch:

  • Coiled so compact molecule so can be stored in small space 
• Characteristics of Starch:

  • The glycosidic bonds can be hydrolysed to form alpha glucose monomers which can be easily transported and used in respiration 
• Characteristics of starch:

  • Amylose alpha glucose monomers are joined by 1, 4 glycosidic bonds 
• Characteristics of starch

  • Amylopectin is a branched polymer with the 1,4 glycosidic bonds between the alpha glucose and 1,6 glycosidic bonds forming between C1 and C6 of adjacent alpha glucose 
• Glycogen is structurally similar to starch but with more branches and shorter chains.
• Characteristics of glycogen

  • Large insoluble polysaccharide formed by condensation reactions between alpha glucose monomers with both 1, 4 and 1, 6 glycosidic bonds, coiled due to 1, 4 glycosidic bonds and branched due to 1, 6 glycosidic bonds. 
• Characteristics of glycogen

  • Insoluble therefore does not affect the water potential of the cell, so water does not move into the cell by osmosis 
• Characteristics of glycogen:

  • Compact molecule so can be stored in small space 
• Characteristics of glycogen:

  • Highly branched so many ends, meaning the glycosidic bonds can be rapidly hydrolysed by enzymes to form alpha glucose monomers which can be easily transported and used in respiration. Animals are more active than plants and have a higher metabolic and respiration rate than plants. 
• Cellulose is a straight, unbranched structural polysaccharide which forms plant cell walls.
• Characteristics of cellulose:

  • Made of beta glucose monomers held together by 1, 4 glyosidic bonds formed by condensation reactions 
• Characteristics of cellulose:

  • Each beta glucose monomer is rotated 180 O  relative to the next resulting in alternate glycosidic bonds 
• Characteristics of cellulose:

  • Many straight chains of beta- glucoses forming parallel to each other. These link together through hydrogen (H) bonds between the many –OH groups, to form bundles called microfibrils which are very strong and support the cell wall and prevent it from bursting when a plant cell becomes turgid. 
• Characteristics of cellulose:

  • Cellulose cannot be digested by mammals because they do not have the appropriate enzyme - cellulase. 
• Isomers- molecules with the same molecular formula as another molecule, but with a different chemical structure.