1 - Biological Molecules

• Monomers - The smaller subunits from which larger molecules are made
• Polymers - Molecules made from a large number of monomers joined
• What is a condensation reaction?

  • A reaction that joins two molecules together
  • with the formation of a chemical bond
  • & involves the elimination of a water molecule
• What is a hydrolysis reaction?

  • A reaction that separates molecules
  • by breaking a chemical bond
  • & involves the use of a water molecule
• Monosaccharides - The monomers from which larger carbohydrates are made

  (e.g. Glucose, Galactose, Fructose)
• What are the two isomers of glucose?

  α-glucose and β-glucose
• Which isomer of glucose is this?

  alpha glucose

  
• Which isomer of glucose is this?

  Beta glucose

  
• How are disaccharides formed?

  By a condensation reaction between two monosaccharides
• 1. Glucose + Glucose --> maltose + water
  2. Glucose + Fructose --> sucrose + water
  3. Glucose + Galactose --> lactose + water
• Describe the test for a reducing sugar (i.e. every monosaccharide except sucrose) (3 marks)?

  • Add Benedict's reagent
  • Heat
  • A positive result is a colour change from blue to green/yellow/orange/red

  
• Why does colour change occur at the top of the test tube first?

  • Heat rises (convection currents)
  • Therefore, reaction occurs at the top of the test tube first

  
• Describe the test for a non-reducing sugar (sucrose) (4 marks)?

  1. Following a negative reducing sugars test
  2. Boil the sample in acid (acid hydrolysis). Then add alkaline solution to neutralise
  3. Add Benedict's reagent + heat
  4. A positive result will go from blue to orange/red
• Describe the test for starch (2 marks)?

  1. Add iodine to the sample
  2. A positive result will go from orange to blue/black

  
• Describe the test for lipids (3 marks)?

  1. Add ethanol and shake to dissolve
  2. Then add distilled water
  3. A positive result is a white emulsion

  
• Describe the test for proteins (2 marks)?

  1. Add biuret reagent to the sample
  2. A positive result will go from blue to purple

  
• Starch:~

  • Monomer = alpha glucose
  • Reactions & Bonds = Condensation forming 1-4 & 1-6 glycosidic bonds
  • Function = Glucose store (Energy source)
  • Where is it found = Starch grains in plant cells
• Starch:~

  • Structure (Amylose) - Joined by 1-4 glycosidic bonds resulting in a spiral shaped polymer
  • Structure (Amylopectin) - Joined by 1-4 & 1-6 glycosidic bonds. The 1-6 bonds result in branches

  
• Starch:~ How does structure relate to function?

  • Large molecule = Insoluble, won't cause osmosis or change the water potential of the cell
  • Spiral shape = Compact so many starch molecules can fit, leading to a lot of storage
  • Branching 1-6 strands of Amylopectin - Larger Surface Area for enzymes to attach, increase rate of hydrolysis when it is broken down
• Glycogen:~

  • Monomer = alpha glucose
  • Reactions & Bonds = Condensation forming 1-4 & 1-6 glycosidic bonds
  • Function = Glucose store (Energy source)
  • Where is it found = In animals, mainly in liver & muscle cells
• Glycogen:~

  Key difference between structure of glycogen & starch is that glycogen contains more 1-6 glycosidic bonds, and is therefore more branched
• Glycogen:~ How does structure relate to function?

  • Large molecule = Insoluble, won't cause osmosis or change the water potential of the cell
  • Branching 1-6 strands - Larger Surface Area for enzymes to attach, increase rate of hydrolysis when it is broken down. Even more branched than starch, so hydrolysis into glucose is faster
• Cellulose:~

  • Monomer = beta glucose
  • Reactions & Bonds = Condensation forming 1-4 glycosidic bonds
  • Function = Structural strength
  • Where is it found = In plants, in the cell wall
• Cellulose:~

  • Long, straight chains of beta glucose
  • Parallel chains held together by hydrogen bonds (forming a fibril)
  • Fibrils are held together by hydrogen bonds to form a cellulose fibre

  
• Cellulose:~ How does structure relate to function?

  • Large size = Insoluble, to not affect the water potential of the cell or affect osmosis
  • Strong polysaccharide = Due to large number of hydrogen bonds between fibrils
• What are two types of lipids?

  1. Triglycerides
  2. Phospholipids
• What type of reaction forms lipids?

  Condensation reaction
• What is a triglyceride made up of & what bond is formed by the condensation reaction?

  • 1 glycerol & 3 fatty acids
  • Ester bond between glycerol and fatty acid (RCOOH)

  
• What is the difference between a saturated & unsaturated fatty acid?

  Saturated - Hydrocarbon chain only contains single C-C bonds

  Unsaturated - Hydrocarbon chain contains at least 1 C-C double bond

  
• Describe the difference between the structure of a phospholipid and triglyceride molecule?

  In phospholipids, one fatty acid is substituted by a phosphate group

  
• The 'head' of a phospholipid is described as being hydrophilic. It attracts water as it is charged. Due to the phosphate group being charged, it repels other fats.

  
  

  The fatty acid chain is not charged. It is known as the hydrophobic ‘tail’ and it repels water but will mix with lipids

  
• Amino acids are the monomers which make up proteins

  
• Left = Amine group

  Right = Carboxylic group

  
• Which part of the amino acid general structure differs in all 20 common amino acids?

  The R group
• Name the reaction that joins amino acids together to form a polypeptide chain and the bond that forms?

  • Reaction = Condensation
  • Bond = Peptide bond
• Proteins are all made up of one or more polypeptide chains folded into highly specific 3D shapes. The primary structure is the sequence of amino acids in a polypeptide chain.

  
  

  The order/sequence the amino acids are bonded in is determined by DNA. This specific order of amino acids will alter where bonds occur and how the protein folds. Therefore, the primary structure determines the final shape and the protein's function.
• Primary Structure - The sequence/order of amino acids in a polypeptide chain

  
• Secondary Structure - The folding of the primary structure into an alpha helix or beta pleated sheet, held in place by hydrogen bonds.

  
• Tertiary Structure - The further folding of the secondary structure creates a unique 3D shape, held in place by hydrogen, ionic and sometimes disulfide bonds.

  
• Quaternary Structure - There is more than 1 polypeptide chain in the protein