Biology_biomolecules

• Living system


  • Grows
  • Sustains
  • Reproduces itself
• A living system is composed of non-living atoms and molecules
• Biochemistry


  The pursuit of knowledge of what goes on chemically within a living system
• Complex biomolecules in living systems

  • Carbohydrates
  • Proteins
  • Nucleic acids
  • Lipids
• Proteins and carbohydrates are essential constituents of our food
• Biomolecules interact with each other and constitute the molecular logic of life processes
• Other important molecules in organisms

  • Vitamins
  • Mineral salts
• Carbohydrates


  Primarily produced by plants, a very large group of naturally occurring organic compounds
• Common examples of carbohydrates

  • Cane sugar
  • Glucose
  • Starch
• The name carbohydrate was derived from the general formula as they were considered as hydrates of carbon
• Not all compounds fitting the general formula are classified as carbohydrates, e.g. acetic acid
• Rhamnose, C6H12O5 is a carbohydrate but does not fit the general formula
• Carbohydrates


  Optically active polyhydroxy aldehydes or ketones or the compounds which produce such units on hydrolysis
• Sugars


  Carbohydrates that are sweet in taste
• Sucrose


  The most common sugar used in our homes
• Lactose


  The sugar present in milk
• Saccharides


  (Greek: sakcharon means sugar)
• Classification of carbohydrates based on hydrolysis

  • Monosaccharides
  • Oligosaccharides
  • Polysaccharides
• Monosaccharides


  Carbohydrates that cannot be hydrolysed further to give simpler units of polyhydroxy aldehyde or ketone
• About 20 monosaccharides are known to occur in nature
• Some common monosaccharides


  • Glucose
  • Fructose
  • Ribose
• Oligosaccharides


  Carbohydrates that yield two to ten monosaccharide units on hydrolysis
• Disaccharides, trisaccharides, tetrasaccharides


  Types of oligosaccharides depending on the number of monosaccharides obtained on hydrolysis
• Common disaccharides


  • Sucrose
  • Maltose
• Polysaccharides


  Carbohydrates which yield a large number of monosaccharide units on hydrolysis
• Common polysaccharides


  • Starch
  • Cellulose
  • Glycogen
  • Gums
• Polysaccharides are not sweet in taste, hence they are also called non-sugars
• Classification of carbohydrates as reducing or non-reducing sugars

  • Reducing sugars
  • Non-reducing sugars
• Reducing sugars


  Carbohydrates which reduce Fehling's solution and Tollens' reagent
• All monosaccharides, whether aldose or ketose, are reducing sugars
• Classification of monosaccharides


  • Based on number of carbon atoms
  • Based on functional group (aldose or ketose)
• Aldose


  Monosaccharide containing an aldehyde group
• Ketose


  Monosaccharide containing a keto group
• Types of monosaccharides based on number of carbon atoms

  • Triose
  • Tetrose
  • Pentose
  • Hexose
  • Heptose
• Glucose occurs freely in nature as well as in the combined form
• Preparation of glucose from sucrose


  1. Boil sucrose with dilute HCl or H2SO4 in alcoholic solution

  2. Glucose and fructose are obtained in equal amounts
• Preparation of glucose from starch

  Hydrolyse starch by boiling with dilute H2SO4 at 393 K under pressure
• Glucose


  An aldohexose, also known as dextrose
• Glucose is probably the most abundant organic compound on earth
• Determination of the structure of glucose

  1. Molecular formula C6H12O6

  2. Reaction with HI forms n-hexane

  3. Reaction with hydroxylamine forms oxime

  4. Reaction with HCN forms cyanohydrin

  5. Oxidation with bromine water forms gluconic acid

  6. Acetylation with acetic anhydride forms glucose pentaacetate