1.2 carbohydrates

• what are monosaccharides

  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

  alpha and beta are isomers so have the same molecular formula but differently arranged atoms
• 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
• function of starch

  energy store in plants
• structure of starch

  polysaccharide of alpha glucose

  amylose is 1-4 glycosidic bonds so unbranched

  amylopectin is 1-4 and 1-6 glycosidic bonds so branched
• function of glycogen

  energy store in animal cells
• structure of glycogen

  polysaccharide of alpha glucose

  1-4 and 1-6 glycosidic bonds so branched
• explain how the structure of starch (amylose) relates to its function

  helical so compact for storage in cell

  large, insoluble polysaccharide molecule so can't leave cell/cross cell membrane

  insoluble in water so water potential of cell not affected (no osmotic effect)
• explain how the structure of starch (amylopectin) relates to its function

  branched so compact/fit more molecules in a small area

  branched so more ends for faster hydrolysis to release glucose for respiration to make ATP for energy release

  large insoluble polysaccharide molecule so can't leave cell/cross cell membrane

  insoluble in water so water potential of cell not affected (no osmotic effect)
• explain how the structure of glycogen relates to its function

  branched so compact/fit more molecules in a small area

  branched so more ends for faster hydrolysis to release glucose for respiration to make ATP for energy release

  large insoluble polysaccharide molecule so can't leave cell/cross cell membrane

  insoluble in water so water potential of cell not affected (no osmotic effect)
• function of cellulose

  provides strength and structural support to plant/algal cell walls
• structure of cellulose

  polysaccharide of beta glucose

  1-4 glycosidic bonds so straight unbranched chains

  chains linked parallel by hydrogen bonds forming microfibrils
• explain how the structure of cellulose relates to its function

  every other beta glucose molecule is inverted in a long straight unbranched chain

  many hydrogen bonds link parallel strands (crosslinks) to from microfibrils (strong fibres)

  hydrogen bonds are strong in high numbers

  so provides strength to plant cell wall
• test for reducing sugars

  add benedict's solution (blue) to sample

  heat in a boiling water bath

  positive result is a green/yellow/orange/red precipitate
• what are reducing sugars

  monosaccharides, maltose, lactose
• test for non-reducing sugars

  do Benedict's test and stays blue/negative

  heat in a boiling water bath with acid (to hydrolyse reducing sugars)

  neutralise with alkali (sodium bicarbonate)

  heat in a boiling water bath with benedicts solution

  positive result is a green/yellow/orange/red precipitate
• what are non-reducing sugars

  sucrose
• method to measure the quantity of sugar in a solution

  carry out benedicts test

  then filter and dry precipitate

  find mass/weight
• method to measure the quantity of sugar in a solution

  make sugar solutions of known concentrations (dilution series)

  heat a set volume of each sample with a set volume of benedict's solution for same time

  use colorimeter to measure absorbance (of light) of each known concentration

  plot calibration curve, concentration on x-axis and absorbance on

  y-axis and draw a line of best fit

  repeat Benedict's test with unknown sample and measure absorbance

  read off calibration curve to find concentration associated with unknown samples absorbance
• biochemical test for starch

  add iodine dissolved in potassium iodide (orange/brown) and shake/stir

  positive result is blue-black