H

• Carbohydrates


  Organic compounds containing C, H, O, formed of polyhydroxy aldehydes or ketones
• Saccharides


  Another name for carbohydrates, from the Greek word "saccharon" meaning sugar
• Carbohydrates


  • Widely distributed in animal and plant tissues
  • Include not only sugar, but also starches found in foods like bread, pasta, and rice
• Term "carbohydrate"


  Comes from the observation that when you heat sugars, you get carbon and water (hence, hydrate of carbon)
• Functions of carbohydrates


  • Source of energy for living beings (e.g. glucose)
  • Storage of energy in the body
  • Cell membrane components that mediate some forms of intercellular communication (receptors)
  • In the form of fibers, lowering blood glucose, cholesterol level and preventing constipation
  • Constituent of nucleic acids RNA and DNA (e.g. ribose and deoxyribose sugar)
• Classification of carbohydrates


  • Monosaccharides (contain a single polyhydroxy aldehyde or ketone unit, e.g. glucose, fructose)
  • Disaccharides (consist of two monosaccharide units linked together by a covalent bond, e.g. sucrose)
  • Oligosaccharides (contain from 3 to 10 monosaccharide units, e.g. raffinose)
  • Polysaccharides (contain very long chains of hundreds or thousands of monosaccharide units, e.g. cellulose, glycogen, starch)
• Monosaccharides


  • Simplest carbohydrates, containing only one polyhydroxy aldehyde or ketone unit
  • Classified according to the number of carbon atoms they contain (triose, tetrose, pentose, hexose)
  • Presence of an aldehyde is indicated by the prefix "aldo-" and a ketone by the prefix "keto-"
• Properties of monosaccharides


  • Most have a sweet taste
  • Solids at room temperature
  • Extremely soluble in water
  • All are reducing sugars
• Disaccharides


  Two monosaccharides linked together through a glycosidic linkage
• Disaccharides that contain hemiacetal groups are reducing sugars
• Oligosaccharides


  Contain from 3 to 10 monosaccharide units
• Polysaccharides


  • Contain hundreds or thousands of carbohydrate units
  • Are not reducing sugars
• Types of polysaccharides


  • Starch
  • Glycogen
  • Cellulose
• Asymmetric carbon


  Carbon atom attached to 4 different chemical groups
• All monosaccharides contain one or more asymmetric carbon except DHA