Biological Molecules

• Define monomer. Give examples

  Smaller units that join togther to form larger molecules:

  - Monosaccharides (glucose, fructose, glactose)

  - Amino acids

  - Nucleotides
• Define polymer. Give examples

  Molecules formed when many monomers join together:

  - Polysaccharides

  - Proteins

  - DNA/RNA
• What happens in a condensation reaction?

  A chemical bond forms between 2 molecules & a molecule of water is produced
• What happens in a hydrolysis reaction?

  A water molecule is used to break a chemical bond between 2 molecules.
• Name the 3 hexose monosaccharides

  ● glucose

  ● fructose

  ● galactose

  all have the molecular formula C6H12O6
• Name the type of bond formed when monosaccharides react

  (1,4 or 1,6) glycosidic bond

  2 monomers= 1 chemical bond= disaccharide

  Multiple monomers= many chemical bonds= polysaccharide
• Name 3 disaccharides. Describe how they form

  maltose (glucose + glucose)

  sucrose (glucose + fructose)

  lactose (glucose + galactose)
• Describe the structure and functions of starch

  Storage polymer of 𝛼-glucose in plant cells:

  ● insoluble = no osmotic effect on cells

  ● large = does not diffuse out of cells

  made from amylose:

  ● 1,4 glycosidic bonds

  ● helix with intermolecular

  H-bonds = compact

  and amylopectin:

  ● 1,4 & 1,6 glycosidic bonds

  ● branched = many terminal ends

  for hydrolysis into glucose
• Describe the structure and functions of glycogen


  Main storage polymer of 𝛼-glucose in animal cells (but also found in plant cells):

  ● 1,4 & 1,6 glycosidic bonds.

  ● Branched = many terminal ends for hydrolysis.

  ● Insoluble = no osmotic effect & does not diffuse out of cells.

  ● Compact.
• Describe the structure and function of cellulose

  Polymer of B-glucose gives rigidity to plant cell walls (prevents bursting under turf or pressure, holds stem up)

  - 1,4 glycosidic bond

  - Straight chain, unbranded molecule

  - Alternate glucose molecules are rotated 180

  - H-bonds cross links between parallel strands from microfibrils= high tensile strength
• Design the Benedict's test for reducing sugars

  1. Add an equal volume of Benedict's reagent to a sample.

  2. Heat the mixture in an electric water bath at 100degrees for 5 mins.

  3. Positive result: colour change from blue to orange & brick-red precipitate forms.
• Describe the Benedict's test for non-reducing sugars

  1. Negative result: Benedict's reagent remains blue

  2. Hydrolyse non-reducing sugars e.g.sucrose into their monomers by adding 1cm3 of HCI. Heat in a boiling water bath for 5 mins.

  3. Neutralised the mixture using sodium carbonate solution.

  4. Proceed with the Benedict's test as usual
• Describe the test for starch

  1. Add iodine solution

  2. Positive result: colour change from orange to blue-black
• Monosaccharides


  A single monomer
• Disaccharide


  Molecules formed by the condensation of two monmosaccharides
• DNA helicase


  An enzyme that breaks the hydrogen bonds between the two DNA strands in the DNA molecules that is going to be replicated
• DNA polymerase


  An enzyme that catalyses the condensation reactions between the new nucleotides
• Glycogen


  Highly branched polysaccharide made of alpha glucose monomers that is used as the main storage of energy in humans and animals
• Semi conservative replication


  The production of two daughter DNA molecules from one DNA molecule which both contain one original DNA strand and one newly synthesised strand.
• Polysaccharides


  More than two monosaccharides joined by condensation reaction
• Main energy storage in plants

  Starch
• Starch


  Mix of two polysaccharides: alpha-glucose= amylose and amylopectin
• Amylose


  Long, unbranded chain of alpha-glucose

  Angle of glycosidic bond= coiled—> compact good for storage
• Amylopectin


  Long, unbranched chain of alpha-glucose

  Sides branches allow enzymes to break down the molecule to break glycosidic bonds easily
• What makes starch good for storage

  Insoluble in water= doesn't affect water potential

  Water doesn't leave by osmosis
• Glycogen structure


  Highly branched—> release energy quickly

  Very compact= good for storage
• Cellulose


  Long, unbranched chain of beta- glucose
• Structure and function of cellulose

  Hydrogen bonds link the chains= strong fibres (micro fibrils)—> provide structural support
• What is a triglyceride made up of?

  3 fatty acids and 1 glycerol
• Fatty acid tail


  Hydrophobic (repel water molecules)
• Fatty acid head


  Hydrophilic (attracts water molecules)
• How is a triglyceride formed

  By a condensation reaction between a fatty acid and a glycerol

  Ester bond is formed

  Happens twice more
• What are the two kinds of fatty acids

  saturated and unsaturated
• What is the difference between saturated and unsaturated

  Hydrocarbon tails (R group)
• Saturated fats


  Don't have any double bonds between their carbon atoms
• Unsaturated fats


  At least one double bond between carbon atoms—> cause chain to kink
• Phospholipid structure


  glycerol + 2 fatty acids + phosphate group
• Structure and function of triglyceride

  Energy storage molecules

  - long hydrocarbon tails= fatty acids contain lots of chemical energy

  - insoluble= don't affcet water potential
• Structure and function of phospholipids

  Make up bilayer of cell membrane (control what enters and leaves)

  - hydrophilic heads, hydrophobic tails= form a double layer

  - centre of bilayer is hydrophobic= water-soluble substances cant pass through- acts as barrier
• Emulsion test for lipids

  1. Shake test substance with ethanol for a minute, pour solution into water

  2. Any lipid will show as milky emulsion

  3. The more lipid the more milky the colour