1 Biological Molecules

• Monomers are smaller, repeating molecules from which larger molecules, polymers, are made
• Polymers are molecules made up of many identical molecules called monomers.
• In a condensation reaction, 2 molecules join together, forming a chemical bond and releasing a water molecule
• In a hydrolysis reaction, 2 molecules are separated by breaking a chemical bond using a water molecule
• fill in the blanks:

  A) nucleotide

  B) starch

  C) amino acid

  
• Monosaccharides are monomers from which larger carbohydrates are made
• Complete the structure of alpha glucose:

  A) H

  B) OH

  C) HO

  D) H

  E) O

  
• Isomers have the same molecular formula, but have differently arranged atoms
• In alpha glucose, the OH group is below carbon-1, whereas in beta glucose, it is above.
• Disaccharides are two monosaccharides joined together with a glycosidic bond, formed by a condensation reaction, releasing a water molecule
• fill in the blanks:

  A) glucose

  B) glucose

  C) glucose

  D) fructose

  E) glucose

  F) galactose

  
• fill in the blanks:

  A) condensation

  B) hydrolysis

  C) glycosidic

  D) H2O

  
• Polysaccharides are many monosaccharides joined together with glycosidic bonds, formed by many condensation reactions, releasing water molecules.
• Glucose is stored as starch in plant cells, whereas in animal cells, it is stored as glycogen.
• Starch is:

  • a polysaccharide of alpha glucose
  • Amylose - 1,4 glycosidic bonds. it is unbranched
  • Amylopectin - 1,4 and 1,6 glycosidic bonds. it is branched
• Glycogen is:

  • A polysaccharide made of alpha glucose
  • Structured by 1,4 and 1,6 glycosidic bonds. it is branched
• fill in the blanks:

  A) amylose

  B) amylopectin

  C) glycogen

  
• fill in the blanks:

  A) 1,4

  B) 1,6

  
• Structure of starch related to its function:

  • Helical, so compact for storage in cell
  • Large, insoluble polysaccharide molecule, so can’t leave cell membrane 
  • Insoluble in water, so water potential of cell not affected (no osmotic effect)
• Structure of glycogen related to its function:

  • Branched, so it is compact and can fit more molecules in small areaBranched, so more ends for faster hydrolysis, so release glucose for respiration to make ATP for energy 
  • Large, insoluble polysaccharide molecule, so can’t leave cell membrane
  • Insoluble in water, so water potential of cell not affected (no osmotic effect)
• Cellulose provides strength and structural to plant cell walls
• Cellulose structure:

  • Polysaccharide of beta glucose
  • Chains linked in parallel by hydrogen bonds forming microfibrils
  • 1,4-glycosidic bond, so it has straight, unbranched chains
• Cellulose structure related to its function:

  • Every other beta 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
• This is the structure of cellulose

  A) beta glucose

  B) 1,4

  C) hydrogen

  
• Reducing sugars include monosaccharides, maltose and lactose
• 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
• Sucrose is a non-reducing sugar
• 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
• To measure the quantity of sugar in a solution, filter and dry the precipitate from the Benedict's solution, and find the mass
• Measuring quantity of sugar in a solution:

  1. Make sugar solutions of known concentrations (eg. 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
• Test for starch:

  • Add iodine solution (orange brown) and shake or stir
  • The positive result is a blue black colour
• Triglycerides and phospholipids are examples of lipids
• Fill in the blanks

  A) Saturated

  B) Unsaturated

  
• Structure of a fatty acid:

  • Variable R group - Hydrocarbon chain
  • -COOH - carboxyl group
• Saturated fatty acids have no C=C double bonds in hydrocarbon chain; all carbons fully saturated with hydrogen
• Unsaturated fatty acids have one or more C=C double bond in hydrocarbon chain creating bend / kink
• Formation of triglycerides:

  1. 1 glycerol molecule and 3 fatty acids
  2. Condensation reaction
  3. Removing 3 water molecules
  4. Forming 3 ester bonds
• fill in the blanks:

  A) glycerol

  B) fatty acids

  C) triglyceride

  D) ester

  
• Function of triglycerides related to its structure:

  • High ratio of C-H bonds to carbon atoms in hydrocarbon chain, so used in respiration to release more energy than same mass of carbohydrates
  • Non-polar fatty acids so insoluble in water (clump together as droplets), so no effect on water potential of cell (or can be used for waterproofing)
• fill in the blanks:phos

  A) phosphate

  B) glycerol

  C) fatty acid

  D) fatty acid