carbohydrates

• MONOMERS: Small units of a polymer that are joined together to form a polymer
• POLYMERS: long chains of monomers joined together by covalent bonds
• CONDENSATION REACTION: A reaction in which two molecules join together to form one molecule with the removal of water from the monomers enabling a chemical bond between monomers
• HYDROLYSIS REACTION: A reaction in which a water molecule is added between two bonded monomers to break chemical bond and is broken down into its constituent parts
• CARBOHYDRATES: key biological molecules store energy and structural support to plant cells
• how are disaccharides formed?

  condensation reaction from smaller molecules of monosaccharides.

  a glycosidic bond is formed between two monosaccharides

  disaccharides:

  MALTOSE: condensation reaction of glucose + glucoose

  SUCROSE: condensation reaction of glucose + fructose

  LACTOSE: condensation reaction of glucose + galactose
• what are the monomers of carbohydrates and their functions?

  • glucose
  • galactose
  • fructose
  • all are sugars, soluble in water
  • provide energy and are building blocks to create other molecules
• how does an alpha glucose and beta glucose differ structurally?

  the H and the OH group is swapped on carbon 1

  alpha glucose: hydroxyl group (-OH) placed below ring on first carbon

  beta glucose: hydroxyl group (-OH) placed above ring

  orientation affects overall shape and stability of glucose
• CARBOHYDRATES ELEMENTS: Carbon, Hydrogen, Oxygen
• TEST FOR REDUCING SUGARS:

  • reducing sugars are all monosaccharides and some disaccharides (maltose and lactose)

  1. add 2cm3 of food sample in test tube, needs to be in liquid form
  2. add equal volume of Benedict's reagent
  3. Heat mixture gently in a boiling tube for five mins
  4. colour of ppt changes from Blue-green-yellow-orange-brick red
  5. higher conc of reducing sugar= further colour goes
  6. main colour change is from blue solution to brick-red ppt
• Test for non-reducing sugars:

  • Non-reducing sugars like sucrose need to be hydrolyzed into monosaccharides components to be detected
  • Procedure:

  1. Test sample with reducing sugar method

  2. If no color change, add 2cm3 of food sample to a test tube and 2cm3 of dilute HCl

  3. Place the test tube in gently boiling water for 5 mins to hydrolyze disaccharides into constituent monosaccharides

  4. Slowly add sodium hydrogen carbonate solution to neutralize HCl

  5. Add 2cm3 of Benedict's reagent in solution and place in gently boiling water for 5 mins

  6. Solution should turn from blue to brick-red if reducing sugar is present from the hydrolysis of non-reducing sugars
• POLYSACCHARIDES: A polymer of monosaccharides formed from condensation reactions of two or more monosaccharides.
• Plants store excess glucose as starch, which is a mix of two polysaccharides: amylose and amylopectin
• Amylose is a long unbranched chain of alpha glucose, the angles of glycosidic bond giving it a coiled structure, making it compact and good for storage
• Amylopectin is a long branched chain of alpha glucose, allowing enzymes to easily break down the molecule and release glucose
• Starch is insoluble in water, doesn't affect water potential, and water can't enter cells by osmosis, making it good for storage
• TEST FOR STARCH:

  test in room temp

  process:

  1. place 2cm3 of sample tested into test tube (or 2 drops of sample into depression on spotting tile)
  2. add two drops of iodine solution, shake and stir
  3. presence of starch is a colour change from orange-brown to blue-black
• GLYCOGEN:

  • in animal cells (and bacteria)
  • excess store of glucose stored as glycogen
  • short chains, highly branched (more than amylopectin)- so stored glucose easily released so energy released easily since more enzymes can act on it, important since animals have high metabolic rates since more active
  • compact: good for storage
  • insoluble: water not drawn out by osmosis
• CELLULOSE:

  • made of long, unbranched chains of beta glucose
  • when beta glucose bond form straight cellulose chains, run parallel to each other
  • chains linked by hydrogen bonds, form cross-linkages
  • cellulose molecules grouped together form microfibrils, arranged parallel groups called fibres
  • in cell walls; provide rigidity, structural support, prevent walls from bursting (from osmosis)