Biological molecules

• What’s a monomer?


  smaller/repeating molecules from which bigger molecules/polymers are made
• What’s a polymer?


  molecule made up of many identical/similar molecules/monomers
• What is a condensation reaction?

  The joining of 2 molecules forming a chemical bond and releasing a water molecule
• What is a hydrolysis reaction?

  When 2 molecules are separated breaking the chemical bond using a water molecule
• What are examples of monomers joining to form monomers?

  Nucleotides -> polynucleotides

  monosaccharides -> polysaccharides

  Amino acids -> polypeptides
• What are monosaccharides (give 3 examples)?

  monomers from which larger carbohydrates are made e.g glucose, fructose, galactose
• Describe the difference between the structure of alpha glucose and beta glucose:

  Alpha:

  OH group is below carbon 1

  Beta:

  OH group is above carbon 1

  A and B glucose are isomers
• What are disaccharides and how are they formed?

  Two monosaccharides joined together with a glycosidic bond formed by a condensation reaction, releasimg a water molecule
• List 3 common disaccharides and monosaccharides from which they’re made:

  Maltose: glucose + glucose

  Sucrose: glucose + fructose

  Lactose: glucose + galactose
• A diagram to show how two monosaccharides are joined together

  
• What are polysaccharides and how are they formed?

  Many monosaccharides joined together with glycosidic bonds formed by condensation reaction releasing water molecule
• Describe the function and structure of starch:

  Energy store in plant cells:

  • polysaccharide of alpha glucose
  • amylose - 1,4 glycosidic bonds so unbranched
  • amylopectin - 1,4 and 1,6 glycosidic bonds so branched
• Describe the function and structure of glycogen:

  Energy store in animal cells:

  • polysaccharide made of alpha glucose
  • 1,4 and 1,6 glycosidic bonds so branched
• Explain how the structure of starch relate to its function:

  1. Helical so compact for storage in cells
  2. large and insoluble polysaccharide so can’t leave cell membrane
  3. insoluble in water so water potential of cell isn’t effected
• Explain how the structure of glycogen relates to its function:

  1. Branched - fit more molecules in a small area
  2. Branched - more ends for faster hydrolysis
  3. Large and insoluble polysaccharide can’t cross cell membrane
  4. insoluble in water so no osmotic effect
• Describe the basic function and structure of cellulose:

  Provides strength and structural support to plant/algae cell walls

  • Polysaccharide of beta 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:

  1. Every other beta glucose is inverted in a long straight unbranched chain
  2. Many hydrogen bonds link parallel strands to form microfibrils
  3. hydrogen bonds are strong in numbers so provides strength
• Describe the test for reducing sugars (monosaccharides, maltose, lactose):

  • Add Benedict solution (blue) to sample
  • Heat in boiling water bath
  • positive result = green/yellow/orange/red precipitate
• Describe the test for non-reducing sugars (sucrose):

  • Do Benedict test and stays blue = negative
  • Heat in boiling water bath with acid to hydrolyse into reducing sugar
  • neutralise with alkali
  • Heat in boiling water bath with benedict solution
  • positive result = green/yellow/orange/red precipitate
• Suggest a method to measure the quantity of sugar in a solution:

  • Carry out Benedict test as above then filter and dry precipitate and find the mass
• What is the test for starch?

  • Add iodine dissolved in potassium iodide (orange/brown)
  • positive result = blue:black
• Name two groups of lipids:

  Triglycerides and phospholipids
• Whats the structure of a fatty acid (RCOOH)

  Variable group - R - hydrocarbon chain and -COOH = carboxyl group
• Describe the difference between a saturated and unsaturated fatty acid:

  Saturated = no carbon double bonds

  Unsaturated = one or more carbon double bonds
• How to triglycerides form?

  1 glycerol molecule and 3 fatty acids join by a condensation reaction removing 3 water molecules and forming 3 ester bonds
• Explain how the properties of triglycerides are related to their structure:

  It’s an energy store:

  • High ratio of C-H bonds to carbon atoms so used in respiration to release more energy than same mass of carbohydrates
  • Hydrophobic fatty acids so insoluble in water so no effect on water potential of the cell
• What’s the difference between the structure of triglycerides and phospholipids?

  One of the fatty acids of a triglyceride is substituted by a phosphate containing group
• How do the properties of phospholipids relate to their structure?

  Form a bilayer in cell membrane allow diffusion of small molecules

  • phosphate heads are hydrophilic - attracted to water
  • fatty acid tails are hydrophobic
• What’s the test for lipids?

  • Add ethanol and shake then add water
  • positive = milky white emulsion
• What’s the general structure of an amino acid?

  COOH = carboxyl group

  R = variable group

  H2N = amine group
• How many amino acids are common in all organisms?

  20
• How do amino acids join together?

  Condensation reaction which removes a water molecule between COOH and NH2 of another forming a peptide bond
• What are dipeptides and polypeptides?

  dipeptide is 2 amino acids joined together

  polypeptide is many amino acids joined together
• What’s the primary structure of a protein?

  Sequence of amino acids in a polypeptide chain joined by peptide bonds
• What’s the secondary structure of a protein?

  Folding of polypeptide chain into alpha helix or beta pleats due to hydrogen binding between amino acids between NH groups and C=O groups
• What’s the tertiary structure of a protein?

  3D folding of polypeptide chain due to interactions between amino acid R groups forming hydrogen bonds, ionic bonds and disulphide bridges
• What’s the quaternary structure of a protein?

  More than one polypeptide chain formed by interactions between polypeptides
• What’s the test for proteins?

  Add biuret reagent (sodium hydroxide + copper sulphate)

  positive result = purple/lilac colour negative stays blue
• How do enzymes act as biological catalysts?

  Each enzyme lowers the activation energy of reaction it catalyses to speed up rate of reaction
• What’s the induced fit model of enzyme action?

  The substrate binds to active site of enzyme causing the active site to change shape so it’s complementary to the substrate so enzyme substrate complex forms causing bonds in substrate to bend lowering activation energy