CARBS

• CARBOHYDRATES - Most abundant macromolecule in the plant world
• CARBOHYDRATES - Literally means hydrate of carbon.
• CARBOHYDRATES

  • Primary source of energy
  • Breads, grains, and pasta are Sources of carbohydrates.
• CARBOHYDRATES

  they act as storehouses of chemical energy (glucose, starch, glycogen)
• A polyhydroxyaldehyde or polyhydroxyketone,or a substance that gives these compounds on hydrolysis.
• The simpler members of the carbohydrate family are often referred to as SACCHARIDES because of their sweet taste (LATIN SACCHARUM “sugar”).
• Examples of Carbohydrates

  1. Glucose (Blood Sugar) C6H12O6
  2. Sucrose (Table Sugar)
  3. Glucose + Fructose
• Monosaccharides - have general formula CnH2nOn with one of the carbons being the carbonyl group of either an aldehyde or a ketone.
• Monosaccharides containing an aldehyde group are classified as aldoses, those containing a ketone group are classified as ketoses.
• Monosaccharides are classified by their number of carbon atoms.
• Most common monosaccharides have three to nine carbon atoms.
• There are only two trioses:

  1. Glyceraldehyde (an aldotriose)
  2. Dihydroxyacetone (a ketotriose)
• Often aldo- and keto- are omitted and these compounds are referred to simply as trioses.
• Although “triose” does not tell the nature of the carbonyl group, it at least tells the number of carbons.
• Glyceraldehyde, the simplest aldose, contains a stereocenter and exists as a pair of enantiomers.
• Fischer projection - a two-dimensional representation for showing the configuration of tetrahedral stereocenters.
• Horizontal lines represent bonds projecting forward from the stereocenter.
• Vertical lines represent bonds projecting to the rear.
• Only the stereocenter is in the plane.
• In 1891, Emil Fischer made the arbitrary assignments od D- and L- to the enantiomers of glyceraldehyde.
• D-monosaccharide: the OH- on its penultimate carbon is on the right in a Fischer projection.
• L-monosaccharide: the OH- on its penultimate carbon is on the left in a Fischer projection.
• The most common D-tetroses and D-pentoses are:

  • D-Erythrose
  • D-Threose
  • D-Ribose
  • 2-Deoxy-D-ribose
• The three most common D-hexoses are:

  • D-Glucose
  • D-Galactose
  • D-Fructose
• Haworth Projections - A five- or six-membered cyclic hemiacetal is represented as a planar ring, lying roughly perpendicular to the plane of the paper.
• Groups bonded to the carbons of the ring then lie either above or below the plane of the ring.
• The new carbon stereocenter created in forming the cyclic structure is called anomeric carbon.
• Stereoisomers that differ in configuration only at the anomeric carbon are called anomers.
• The anomeric carbon of an aldose is C-1; that of the most common ketoses is C-2.
• β means that the -OH on the anomeric carbon is on the same side of the ring as the terminal -CH2OH.
• α means that the -OH on the anomeric carbon is on the side of the ring opposite from the terminal -CH2OH.
• A six-membered hemiacetal ring is called a pyranose, and a five-membered hemiacetal ring is called a furanose.
• Classification of Carbohydrates Based on Number

  of Sugar Units

  • Monosaccharide

  Examples: glucose, fructose, ribose

  • Disaccharide

  Examples: sucrose, lactose, maltose

  • Polysaccharide

  Examples: starch, glycogen
• Chirality - the Handedness of Molecules
• 2 types of isomers

  • Stereoisomers
  • Constitutional Isomers
• 2 types of stereoisomers:

  • achiral
  • chiral
• achiral - without stereocenters
• chiral - with stereocenters
• Achiral

  • Cis-Trans Isomers

  Chiral

  • Enantiomers
  • Diastereomers
• Chirality is derived from the Greek word “kheir” meaning hand. An object is said to be chiral if the object and its mirror image are non- superimposable.