Biochem

• Biochemistry


  A sub-discipline of chemistry and biology which can be divided into structural biology, enzymology and metabolism
• Biochemistry


  The study of the chemical substances found in living organisms and their chemical interactions
• Biochemistry


  Deals with the structures, functions, interactions and bonding of biological macromolecules (carbohydates, lipids, proteins, and nucleic acids)
• Applications of Biochemistry


  • Medicine
  • Nutrition
  • Agriculture
• Photosynthesis


  CO2 + H2O + solar energy → carbohydrates + O2
• Carbohydrates


  • The most abundant organic compounds in the plant world
  • Provide chemical energy, supportive structures, and essential components of nucleic acids
  • Approximately three-fourths of the dry weight of plants
  • Less than 1% of the body weight of animals is made up of carbohydrates
• Carbohydrate


  Hydrate of carbon, with the general formula Cn(H2O)m
• Carbohydrates


  Polyhydroxyaldehydes, polyhydroxyketones, or compounds that yield them after hydrolysis
• Saccharides


  Simpler members of the carbohydrate family, often referred to as such due to their sweet taste
• Classification of Carbohydrates


  • Monosaccharides
  • Oligosaccharides
  • Polysaccharides

  
• Monosaccharides


  • Triose
  • Tetrose
  • Pentose
  • Hexose
  • Heptose
  • Octose

  
• Disaccharide


  A carbohydrate that contains two monosaccharide units covalently bonded to each other

  
• Polysaccharide


  A polymeric carbohydrate that contains many monosaccharide units covalently bonded to each other
• Chiral center


  A carbon atom with four different groups attached to it in a tetrahedral orientation, possessing handedness
• Stereoisomers


  • Enantiomers
  • Diastereomers

  
• Enantiomers


  Stereoisomers whose molecules are nonsuperimposable mirror images to each other
• Diastereomers


  Stereoisomers whose molecules are not mirror images of each other

  
• 1. monosaccharide


  The -OH on its penultimate carbon is on the right in a Fischer projection

  
• 1. monosaccharide


  The -OH on its penultimate carbon is on the left in a Fischer projection

  
• The distinctly different natural flavors "spearmint" and "caraway" are generated by molecules that are enantiomers interacting with chiral "taste receptors"
• Monosaccharides


  Colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol
• Sweetness of carbohydrates relative to sucrose

  • Fructose (1.74)
  • Glucose (1.00)
  • Galactose (0.97)
  • Sucrose (0.74)
  • Lactose (0.32)
  • Honey (0.16)
• Artificial sweeteners


  Sugar substitutes that provide extra sweetness without the added calories
• Artificial sweeteners


  • Saccharin
  • Sodium cyclamate
  • Aspartame
• 1. Glucose


  • Tastes sweet, nutritious, and is an important component of the human diet
  • Also known as blood sugar or dextrose
  • Primary source of energy for cells
  • A 5% (m/v) glucose is often used in hospitals as an intravenous source of nourishment
• 1. Fructose


  Another 6-carbon monosaccharide, found in fruits and honey

  
• 1. Galactose


  • A 6-carbon aldohexose found in the disaccharide lactose (milk sugar)
  • Important constituent of membranes in the brain and nervous system
  • Accumulation can lead to galactosemia, a serious condition
• Cyclic forms of monosaccharides

  Form hemiacetals, with a 6-membered ring called a pyranose and a 5-membered ring called a furanose

  
• Haworth projections


  Represent the cyclic forms of monosaccharides, with α and β anomers

  
• Mutarotation


  The change in specific rotation that accompanies the equilibration of α and β anomers in aqueous solution
• Chair conformations


  The more accurate representation of pyranose rings, with substituents preferring equatorial positions
• Characteristic reactions of monosaccharides

  • Formation of glycerides
  • Reduction to alditols
  • Oxidation to an aldonic acid (reducing sugars)
  • Oxidation to uronic acid

  
• Hemiacetal


  Cyclic structure common to all carbohydrates

  
• Cyclic Conformers of Pyranose

  • Chair conformer favored over boat conformer
  • Large substituents tend to occupy equatorial positions
• Of all the D-aldohexoses, β-D-glucose is the only one where all the bulky -OH groups can be equatorial
• Chair Conformations


  For pyranoses, the six-membered ring is more accurately represented as a chair conformation
• In both Haworth projections and chair conformations, the orientations of groups on carbons 1- 5 of b-D-glucopyranose are up, down, up, down, and up

  
• Characteristic Reactions of Monosaccharides

  • Formation of Glycerides
  • Reduction to Alditols
  • Oxidation to an Aldonic Acid (reducing sugars)
  • Oxidation to Uronic Acids
  • Formation of Phosphoric Esters

  
• Formation of Glycosides (Acetals)

  1. Treatment of a monosaccharide with an alcohol yields an acetal

  2. A cyclic acetal derived from a monosaccharide is called a glycoside

  3. The bond from the anomeric carbon to the -OR group is called a glycosidic bond

  4. Glycosides are stable in water and aqueous base, but like other acetals, are hydrolyzed in aqueous acid to an alcohol and a monosaccharide

  5. Glycosides are named by listing the alkyl or aryl group bonded to oxygen followed by the name of the carbohydrate in which the ending -e is replaced by -ide

  
• Glycoside examples


  • methyl β-d-glucopyranoside
  • methyl β-d-ribofuranoside