biological molecules

• functions of water:

  • reactant
  • solvent
  • transports substances
  • temperature control
  • habitat
• because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with a slight positive charge

  the unshared electrons on the oxygen atom give it a slight negative charge
• high specific heat capacity

  hydrogen bonds between water molecules can absorb lots of energy so lots of energy is needed to raise the temperature of 1 gram of water by 1ºC
• waters high specific heat capacity makes it a good habitat as it is stable
• high latent heat of evaporation

  lots of energy is needed to break the hydrogen bonds between water molecules so lots of energy is used up when water evaporates
• waters high latent heat of evaporation makes it great for cooling
• cohesion is the attraction between molecules of the same type
• water molecules are cohesive as they’re polar
• cohesion helps water to flow, and makes it good for transporting substances and in transpiration streams
• water molecules are held further apart in ice than in liquid water as each water molecule forms 4 hydrogen bonds to other water molecules ~ lattice shape
• ice is less dense than water which means it floats

  this is useful for living organisms as ice insulates water underneath so they can still move around and respire
• water is polar therefore is a good solvent ~ the slightly positive end of a water molecule is attracted to the negative ion, and the slightly negative water molecule end attracts to the positive ion - ions are totally surrounded in water so dissolve
• glucose is a monosaccharide with six carbon atoms (hexose monosaccharide)
• alpha glucose OH and H order:

  OH H OH OH
• beta glucose OH and H order

  OH H OH H
• glucose’s chemical bonds contain lots of energy
• ribose is a pentose monosaccharide
• ribose OH and H order

  H OH OH H
• monosaccharides are joined by glycosidic bonds
• during synthesis, a hydrogen atom on one monosaccharide bonds to a hydroxyl group on the other which releases a molecule of water
• sucrose = a glucose + fructose
• lactose = a / b glucose + galactose
• maltose = a glucose + a glucose
• starch is insoluble in water so doesnt cause water to enter cells by osmosis, which would make them swell
• starch is a mixture of two polysaccharides of alpha-glucose
• amylose is a long, unbranched chain of alpha-glucose

  the angles of the glycosidic bonds give it a coiled structure, making amylose compact therefore good for storage
• amylopectin is a long, branched chain of alpha glucose

  its side branches allow enzymes that breaks down the molecule to get at the glycosidic bonds easily
• glycogen is the main energy storage material in animals
• glycogen is a polysaccharide of alpha glucose
• glycogen has lots of side branches therefore glucose can be released quickly
• glycogen is a compact molecule, therefore good for storage
• cellulose is made of long, unbranded chains of beta-glucose
• when beta glucose molecules bond, they form straight cellulose chains which are linked together by hydrogen bonds to form strong microfibrils
• the strong fibres mean cellulose provides structural support for cells
• triglycerides have one molecule of glycerol with three fatty acids attached
• triglycerides are synthesised by the formation of an ester bond between each fatty acid and the glycerol molecule
• one triglyceride has three ester bonds
• fatty acid molecules have long hydrocarbon tails which are hydrophobic (making fatty acids insoluble in water)
• all fatty acids have the same basic structure:

  the hydrocarbon tail varies

  
• phospholipids have two fatty acid molecules ester bonded to a glycerol molecule and a phosphate group attached