carbohydrates

• Carbs: include:

  • monosaccharides
  • disaccharides
  • oligosaccharides (3-10 monomers)
  • polysaccharides
• the monomers:

  called: monosaccharides = sugars

  • taste sweet
  • have a general formula (CH2O)n
  • where n = 3, 5 or 6
  • contain functional group: OH (hydroxyl - defining feature)
  • are polar and dissolve in water
• • n = 3 formula is C3H603 and sugar is triose (sugar involved in respiration and p/s)
  • n = 5 formula is C5H1005 and sugar is called pentose (ribose (in RNA and ATP) Deoxyribose (in DNA) ribulose 1,5 bis phosphate (RuBP, yr13))
• • n = 6 formula is C6H1206 and sugar is called hexose e.g:
  • glucose = transport sugar in animals and the main respiratory substrate
  • fructose = found in fruit, part of the transport sugar in plants
  • galactose = part of sugar found in mammalian milk
  • all hexoses are structural isomers: same chemical formula, but different molecular structure
• the structure of alpha glucose: C6H1206

  A) 1

  B) 2

  C) 3

  D) 4

  E) 5

  F) 6

  
• Beta glucose:

  
• alpha glucose:

  • -OH on carbon 1 is below the plane of the ring => (H on Carbon 1 is above plane of ring)
  • (OH on C, and OH on C4 same side of ring)

  beta glucose:

  • -OH on Carbon 1 is above the plane of the ring => (H on Carbon 1 is below the plane of the ring)
• Glucose:

  • number of carbons: 6
  • number of carbon in the ring: 5
  • type of ring: 6 membered
  • oxygen atom present in the ring?: yes
  • chemical formula: C6H1206
• Fructose:

  • number of carbons: 6
  • number of carbon in the ring: 4
  • type of ring: 5 membered
  • oxygen atom present in the ring?: yes
  • chemical formula: C6H1206

  
• Ribose:

  • number of carbons: 5
  • number of carbon in the ring: 4
  • type of ring: 5 membered
  • oxygen atom present in ring?: yes
  • chemical formula: C5H1005

  
• Disaccharides:

  • 2 monosaccharides joined together by a condensation reaction C6H12O6 (monosaccharides all hexoses)
  • have general formula (C6H1206) - (H2O) = C12H22011
  • i, ii, iii
• i) Maltose:

  • present in germinating seeds
  • function: source of energy for germination
  • structure:

  
• The bond formed between 2 monosaccharides is called a glycosidic bond

  disaccharides are broken back to monosaccharides by a hydrolysis reaction
• ii) Sucrose

  • function: transport sugar in phloem in plants
  • structure: composed of alpha glucose and fructose, a non reducing sugar

  
• iii) Lactose:

  • function: milk sugar
  • structure: composed of glucose and beta galactose, joined together by a beta 1,4 glycosidic bond

  
• Polymers of Carbohydrates: Polysaccharides

  • long chain carb molecules made up of condensed monosaccharides
  • there are 3 common types, all of which are polymers of glucose
  • have general formula: (C6H1206)x - (H20)x-1 or (C6H1005)x + (H20)
  • x = number of monomers
• polysaccharides:

  • starch: storage carb in plants
  • found in chloroplasts = amyloplasts: insoluble => doesn't affect water potential
  • found in grain: seed germination
  • found in tubers: for asexual reproduction
• there are 2 types of starch:

  • amylose: 20% of starch, monomer: alpha glucose, bonds: alpha 1,4 glycosidic bonds, structure: helical molecule, helix held together by intramolecular H bonds ( strong bonds that hold atoms together within a molecule), relative molecular mass around 50,000 => about 300 glucose residues in a molecule of amylose
  • amylopectin: 80% of starch, monomer: alpha glucose, relative molecular mass around 500,000 => about 3000 glucose residues in a molecule of amylopectin, bonds: alpha 1,4 glycosidic bonds and alpha 1,6 glycosidic bonds (branched)
• Amylose:

  A) 3

  B) 4

  
• amylopectin:

  A) 1

  B) 4

  C) 1

  D) 6

  E) alpha 1,6 glycosidic bond

  
• polysaccharides: Glycogen:

  • storage carb found in animal cells
  • monomer: alpha glucose
  • structure: highly branched
  • bonds: alpha 1,4 glycosidic bonds and alpha 1,6 glycosidic bonds
  • up to 60,000 glucose residues in a molecule of glycogen
• amylopectin and glycogen are good energy stores because they are:

  • compact
  • insoluble
  • branched

  why does this make a good energy store?

  • store a lot in a cell
  • be present but not effect water potential
  • can be broken down faster
• Qualitative tests for reducing and non-reducing sugars

  the presence of sugars can be shown by the benedicts test, there are two types:

  • benedict's test for reducing sugars: Cu 2+ (blue solution) ----> Cu+ (red ppt), positive test for presence of reducing sugars = blue -> brick red precipitate. (all sugars are reducing except sucrose)
  • Benedict's test for non-reducing sugar: it must first be hydrolysed to glucose and fructose before giving a positive test for sucrose: 1. Sucrose -- heat + HCL----> glucose and fructose, 2. neutralise pH by adding NaHCO3, 3. heat with benedicts