2.1.2 biological molecules

• what is in a carbohydrate


  carbon, hydrogen and oxygen
• what is in a lipid


  carbon, hydrogen and oxygen
• what is in a protein

  carbon, hydrogen, oxygen, nitrogen and sulfur
• what is a nucleic acid

  carbon, hydrogen, oxygen, nitrogen and phosphorous
• calcium ions (Ca2+)


  involved in muscle contractions and nerve impulse transmission
• sodium ions (Na+)


  involved in co-transport, kidney function and nerve impulse transmission
• potassium ions (K+)


  involved in stomatal opening and nerve impulse transmission
• hydrogen ions (H+)


  pH determination and catalysis of reactions
• ammonium ions (NH4+)


  involved in the nitrogen cycle where bacteria converts ammonium ions into nitrate ions
• nitrate (NO3-)


  mineral ion absorbed by plants to provide a source of nitrogen to make amino acids
• hydrogencarbonate (HCO3-)


  maintains blood pH
• chloride (Cl-)


  provides a negative charge to balance positive sodium ions and potassium ions in cells
• phosphate (PO43-)


  involved in the formation of phospholipids for cell membranes, nucleic acid and ATP formation and in making bones
• hydroxide (OH-)


  changes the pH making it more alkaline
• how is water a polar molecule

  water is a polar molecule due to the unevenly distributed charge as oxygen is negative and hydrogen is positive

  • Hydrogen bonds form between the oxygen and hydrogen atoms as the positive and negative regions interact.
  • Individual hydrogen bonds are weak but collectively provide strength
• 4 properties of water

  • Solvent in reactions
  • Transport medium
  • Coolant
  • Provides habitat
• water as a solvent

  • Polar (hydrophilic) molecules dissolve readily in water due to the fact water is polar
  • the slight positive charge on hydrogen atoms will attract any negative solutes and the slight negative charge on the oxygen atoms of water will attract any positive ions in solutes
  • Non-polar (hydrophobic) molecules cannot dissolve in water and are repelled by water
  • The cytosol in eukaryotic and prokaryotic cells is mainly water so this ensures many solutes can dissolve within the cell and be easily transported
• water as a transport medium

  • Polar substances dissolve and are easily transported in water around animals and plants either in the blood of animals or the xylem of plants to cells they are needed in inside of the organism
  • Cohesion = water molecules 'sticking' together by hydrogen bonds
  • Due to cohesion water moves up the xylem in plants due to transpiration it is a continuous column of water.
  • This is advantageous as it is easier to draw up a column rather than individual molecules
• water as a coolant

  • water has a high specific heat capacity meaning a lot of energy is required to raise the temperature due to the energy required to break the hydrogen bonds between water molecules
  • This is an advantage as the internal temperatures of plants and animals should remain relatively constant. This is important so that enzymes do not denature or reduce in activity with temperature fluctuations
• water as a coolant (2)

  • Water has a large latent heat of vapourisation (a lot of energy is required to convert water from its liquid state to a gas state) due to the energy required to break the hydrogen bonds between water molecules to turn it into a gas - providing a cooling effect when animals sweat or plants transpire
• water as a habitat

  • water acts as a buffer meaning it provides a stable environment in terms of temperature for aquatic organisms
  • Cohesion provides surface tension to water. This enables small invertebrates to move and live on the surface providing them a habitat away from predators within the water
  • Ice is less dense than liquid water due to the hydrogen bonds. Therefore ice floats on top of water providing a surface habitat for animals
• what is a monomer


  smaller units which can create larger molecules
• what is a polymer


  made from lots of monomers bonded together
• what are the monosaccharides

  glucose, fructose and galactose
• what are disaccharides


  maltose, sucrose and lactose
• what are polysaccharides


  starch, cellulose and glycogen
• 2 isomers of glucose

  • alpha glucose -OH is below
  • Beta glucose is all the same however the -OH group is above
• disaccharides - structure

  • made up of 2 monosaccharides 
  • joined together by a glycosidic bond formed via a condensation reaction forming water as a by-product
• maltose


  glucose + glucose
• sucrose 


  glucose + fructose
• lactose 


  glucose + galactose
• condensation reaction


  joining 2 molecules together by removing water and a chemical bond is formed
• hydrolysis reaction


  splitting apart 2 molecules through the addition of water and a chemical bond is broken
• starch structure


  Starch is made up of 2 polymers and is a store of glucose in plants. It is compact to fit lots of glucose in a small space and a branched structure increases the surface area for rapid hydrolysis back to glucose and is insoluble therefore won't affect water potential
• amylose

  • alpha glucose
  • 1,4 glycosidic bonds
  • Unbranched
• amylopectin

  • alpha glucose
  • 1,4 and 1,6 glycosidic bonds
  • Branched
• cellulose

  • beta glucose
  • 1,4 glycosidic bonds
  • Structure and strength of cell walls in plants
  • Polymer forms long, straight chains held in parallel by hydrogen bonds to form fibrils which combine to form cellulose fibre
  • Many hydrogen bonds provide collective strength
  • Insoluble
• glycogen

  • alpha glucose
  • 1,4 and 1,6 glycosidic bonds
  • Store of glucose in animals
  • Highly branched molecule which increases the surface area for rapid hydrolysis back to glucose

  Insoluble
• Triglycerides


  glycerol and 3 fatty acids
• Phospholipids


  glycerol, 2 fatty acids and a phosphate group