Biology

• Monomers


  Smaller / repeating molecules from which larger molecules / polymers are made
• Polymers


  Molecules made up of many identical / similar molecules / monomers
• Condensation reaction


  1. 2 molecules join together

  2. Forming a chemical bond

  3. Releasing a water molecule

  
• Hydrolysis reaction

  1. 2 molecules separated

  2. Breaking a chemical bond

  3. Using a water molecule

  
• Polymers

  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic Acids
• Monosaccharides

  Monomers from which larger carbohydrates are made
• Monosaccharides

  • Glucose
  • Fructose
  • Galactose
• α-glucose

  OH group is below carbon 1
• β-glucose

  OH group is above carbon 1
• Disaccharides

  Two monosaccharides joined together with a glycosidic bond
• Formation of disaccharides

  Condensation reaction, releasing a water molecule

  
• Polysaccharides


  Many monosaccharides joined together with glycosidic bonds
• Formation of polysaccharides

  Many condensation reactions, releasing water molecules

  
• Starch

  • Energy store in plant cells
  • Polysaccharide of α-glucose
  • Amylose - 1,4-glycosidic bonds → unbranched
  • Amylopectin - 1,4- and 1,6-glycosidic bonds → branched
• Glycogen


  • Energy store in animal cells
  • Polysaccharide made of α-glucose
  • 1,4- and 1,6-glycosidic bonds → branched
• Structure of starch (amylose)

  • Helical → compact for storage in cell
  • Large, insoluble polysaccharide molecule → can't leave cell / cross cell membrane
  • Insoluble in water → water potential of cell not affected (no osmotic effect)
• Structure of glycogen (and starch amylopectin)

  • Branched → compact / fit more molecules in small area
  • Branched → more ends for faster hydrolysis → release glucose for respiration to make ATP for energy release
  • Large, insoluble polysaccharide molecule → can't leave cell / cross cell membrane
  • Insoluble in water → water potential of cell not affected (no osmotic effect)

  
• Cellulose


  • Provides strength and structural support to plant / algal cell walls
  • Polysaccharide of β-glucose
  • 1,4-glycosidic bond → straight, unbranched chains
  • Chains linked in parallel by hydrogen bonds forming microfibrils
• Structure of cellulose

  • Every other β-glucose molecule is inverted in a long, straight, unbranched chain
  • Many hydrogen bonds link parallel strands (crosslinks) to form microfibrils (strong fibres)
  • Hydrogen bonds are strong in high numbers
  • So provides strength to plant cell walls
• 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 / red precipitate
• Test for non-reducing sugars

  1. Do Benedict's test and stays blue / negative

  2. Heat in a boiling water bath with acid (to hydrolyse into reducing sugars)

  3. Neutralise with alkali (eg. sodium bicarbonate)

  4. Heat in a boiling water bath with Benedict's solution

  5. Positive result = green / yellow / orange / red precipitate
• Measure quantity of sugar in a solution

  1. Carry out Benedict's test, then filter and dry precipitate

  2. Find mass / weight