Carbohydrates + Nuclei Acids

• MONOSACCHARIDES

  • 2 families based on position of most oxidised carbon

  
• Pentose and hexose are cyclic

  • Aldehydes and ketone groups react with an alcohol group to produce hemiacetals or hemiketals

  
• Hemiacetal formation generates two different isomeric forms (anomers) at the C1 carbon atom (green *), the anomeric C atom:

  
• Nomenclature: sugars that have a 6-membered ring (5C + O) are called pyranoses; those with 5-membered rings- furanoses

  • pentoses more commonly form furanoses and hexoses more commonly form pyranoses- but some monosaccharides can form both 'ring sizes'

  
• DISACCHARIDES

  • monosaccharides linked by a glycosidic bond: the aromatic carbon reacts with an -OH group on the 2nd monosaccharide (hemicacetal -> acetal)

  
• Straighter chain disaccharide formation:

  
• POLYSACCHARIDES

  • HOMOGLYCANS: homopolysaccharides containing only one type of monosaccharide
  • HETEROGLYCANS: heteropolysaccharides containing residues of more than one type of monosaccharide
• GLUCOSE STORAGE

  • D-Glucose is stored intracellularly in polymeric forms (PLANTS- starch, ANIMALS + FUNGI- glycogen)
  • starch is a mixture of amylose and amylopectin

  -->amylose (D-glucose linked by α1-4 glycosidic bonds)
• AMYLOPECTIN

  • chains will spiral as in amylose, but have branches due to α1-4 glycosidic bonds
  • Branches = increased compactness
  • increased no. of chain ends (faster formation + degradation)
• GLYCOGEN

  • Larger than amylopectin (more glucose units) and more branches (every 8-12 residues)
  • more compact structure and fast metabolism
• CELLULOSE

  • Component of plant cell wall
  • the most abundant biopolymer on earth
  • β1-4 linkages- relatively straight and unbranched chains
  • Adjacent chains hydrogen binds
  • Forms fibrils which associate into a high strength insoluble polymer
• Carbohydrates can be linked to proteins

  • many are components of cell membranes (> cell recognition and cell adhesion)
  • proteins secreted from cells (e.g. blood serum proteins)
  • glycosylation stabilises, slows down removal by kidneys

  1. Elactase, a secreted serum glycoprotein with linked carbohydrates on its surface
  2. Several monosaccharide units can attach to proteins
• NUCLEI ACIDS

  • polynucleotides- nuclei acid biopolymers are composed of nucleotide monomers
  • Nucleotides monomers are composed of:

  1. 5 carbon sugar
  2. heterocyclic nitrogenous base
  3. phosphate group(s)

  • Nucleotides: phosphate group and aromatic nitrogenous base attached to ribose unit
• DNA DINUCLEOTIDE

  • deoxynucleotide triphosphate (dNTPs) are joined by a phosphodiester linkage
  • inorganic pyrophosphate is a leaving group on formation of linkage
• BASE PAIRING IN DNA

  • Purine (2 rings, A,G) -> Pyrimidine (1 ring, T,C)
  • Two hydrogen bonds (A=T), Three hydrogen bonds (G=-C)
• SHORT SEGMENT OF A DNA MOLECULE

  • 2 polynucleotides associate to form a double helix
  • plant aromatic nitrogenous base H-bond to give a 'ladder' of base-pairs (on inside)
  • phosphodiester backbone (on outside)
  • genetic info is varied by the sequence of base pairs