Carbohydrates

• What are monosaccharides? give 3 examples

  • Monomers from which larger carbohydrates are made
  • Glucose, Fructose, Galactose
• Describe the difference between the structure of Alpha Glucose and Beta Glucose

  OH group is below carbon 1 in Alpha Glucose but above carbon 1 in Beta Glucose
• What is an Isomer and give an example?

  Isomer: Molecules with the same molecular formula but differently arranged atoms Example: Alpha and Beta Glucose
• What are Disaccharides and how are they formed?

  • Two monosaccharides joined together with a glycosidic bond
  • Formed by a condensation reaction, releasing a water molecule
• Which monosaccharides make up the disaccharide Maltose?

  Glucose + Glucose
• Which monosaccharides make up the disaccharide sucrose?

  Glucose + Fructose
• Which monosaccharides make up the disaccharide Lactose?

  Glucose + Galactose
• what are polysaccharides and how are they formed?

  • Many monosaccharides joined together with glycosidic bonds
  • Formed by a condensation reactions, releasing water molecules
• Describe the basic function and structure of starch

  Function = Energy store in plants cells

  Structure:

  • Polysaccharide of a-glucose
  • Amylose - 1,4 glycosidic bonds - unbranched
  • Amylopectin - 1,4 and 1,6 glycosidic bonds - branched
• Describe the basic function and structure of Glycogen

  Function = Energy store in animal cells

  Structure:

  • Polysaccharide of a-glucose
  • 1,4 and 1,6 glycosidic bonds - branched
• Explain how the structure of starch (amylose) relates to its function

  • Helical - compact for storage in cell
  • Large, insoluble polysaccharide molecule - can't cross cell membrane
  • Insoluble in water - water potential of cell not affected (no osmotic affect)
• Explain how the structure of glycogen (and starch amylopectin) relates to its function

  • Branched - compact/fit more molecules in small area
  • Branched - more ends for faster hydrolysis - releases glucose for respiration to make ATP for energy release
  • Large, insoluble polysaccharide molecule - can't cross cell membrane
  • Insoluble in water - water potential of cell not affected (no osmotic effect)
• Describe the basic function and structure of cellulose

  Function = provides strength and structural support to plant/algal cell walls

  Structure:

  • Polysaccharide of B-glucose
  • 1,4 glycosidic bond - straight, unbranched chains
  • Chains linked in parallel by hydrogen bonds forming microfibrils
• Explain how the structure of cellulose relates to its function

  • Every other B-glucose molecule is inverted in a long, straight, unbranched chain
  • Many hydrogen bonds link parallel strands to form microfibrils
  • Hydrogen bonds are strong in high numbers
  • So provides strength to plant cell walls
• What are the reducing sugars?

  • Monosaccharides
  • Maltose
  • Lactose
• Describe the test for reducing sugars

  1. Add Benedict's solution (blue) to sample
  2. Heat in a boiling water bath
  3. Positive result = green/yellow/orange/brick red precipitate
• What is the non-reducing sugar?

  Sucrose
• Describe the test for non-reducing sugars

  1. Do Benedict's test and stays blue/negative
  2. Heat in a boiling water bath with acid e.g. HCl (to hydrolyse into reducing sugars)
  3. Neutralise with alkali e.g. Sodium hydroxide
  4. Heat in a boiling water bath with benedict's solution
  5. Positive result = green/yellow/orange/brick red precipitate
• Suggest a method to measure the quantity of sugar in a solution

  • Carry out Benedict's test then filter and dry precipitate
  • Find mass/weight
• Suggest another method to measure the quantity of sugar in a solution

  1. Make sugar solutions of known concentrations (e.g. dilution series)
  2. Heat a set volume of each sample with a set volume of Benedict's solution for same time
  3. Use colorimeter to measure absorbance (of light) of each known concentration
  4. Plot calibration curve - concentration on x axis, absorbance on y axis and draw line of best fit
  5. Repeat Benedict's test with unknown sample and measure absorbance
  6. Read off calibration curve to find concentration associated with unknown sample's absorbance
• Describe the biochemical test for starch

  1. Add iodine dissolved in potassium iodide (orange/brown) and shake/stir
  2. Positive result = blue-black