water and lipids

• what is water a major component of

  cells
• why does water have unusual properties

  its polar and forms hydrogen bonds
• why is there an uneven distribution of electrons

  shared electrons in each O---H covalent bond are not distributed evenly between the O and H nuclei because oxygen is more electronegative

  = large nucleus so more protons = more positive therefore electrons are attracted there
• what does it mean when the electrons have a greater attraction towards the oxygen nucleus as they orbit


  - the O has a slight negative charge

  - the H has a slight positive charge
• what type of bond is between the O and H

  covalent
• are O and H ions


  no
• are hydrogen bonds weak

  individually yes but they are often numerous so are collectively strong= strongest of theintermolecular forces

  - inter = between molecules
• what type of bonding is stronger than hydrogen bonding

  covalent

  - intramolecular = within
• what are hydrogen bonds responsible for


  - waters special properties:

  high specific heat capacity, large latent heat of vaporisation, strong cohesion + surface tension

  
  

  - the 3D shape of polar molecules
• what are waters 5 special properties

  1. metabolite

  
  

  2. solvent for ions + polar molecules

  
  

  3. high specific heat capacity

  
  

  4. large latent heat of vaporisation

  
  

  5. strong cohesion between water molecules
• what two things is water a solvent for


  1. ions

  = salt dissolves in water as water molecules are attached to the ions

  
  

  2. polar molecules
• examples of polar groups


  - hydroxyl group- carboxyl group- amine group- carbonyl group

  = can all form hydrogen bonds with water=hydrophilic
• what does it mean if a molecule contains a polar group


  able to dissolve in water

  = soluble but it depends on the size of the non polar part of the molecule
• what happens if the non polar part of the molecule is small

  
  

  soluble
• what happens if the non polar part of the molecule is large

  
  

  hydrophobic

  = cannot interact with water
• metabolite significance


  its an important metabolite in many metabolic reactions

  = eg. condensation, hydrolysis, photosynthesis + respiration
• solvent for ions + polar molecules significance


  readily dissolves substances like:

  - gases (O2 + CO2)

  - wastes (ammonia + urea)

  - inorganic ions/small hydrocarbon molecules (amino acids, monossacharides + ATP)

  - enzymes (whose reactions take place in solution)

  
  

  = water can transport these substances + provide the site for their chemical reactions
• high specific heat capacity significance


  takes a lot of energy for water to change temperature

  = water heats up + cools down slowly, buffering changes in temperature

  = organisms + aquatic environments can maintain a relatively stable temperature more easily
• large latent heat of vaporisation significance


  takes a lot of energy for water to transform from liquid to gas

  = evaporation has a significant cooling effect because of amount of energy needed eg. sweating
• strong cohesion between water molecules significance


  water can move in long unbroken columns along vessels

  = allows water to be pulled up a tube eg. xylem in plants (transpiration stream)

  = creates surface tension so water surfaces act like a skin + can support small organisms in aquatic environments eg. pond skater
• what are lipids

  macromolecules

  = not polymers as no single repeating unit
• what elements do lipids contain


  C, H, O
• are lipids soluble

  insoluble in water but soluble in alcohol
• what are the two main lipids


  triglycerides and phospholipids
• what are fats made of


  saturated fatty acids
• saturated


  no double bond
• what are triglycerides made from


  1 molecule of glycerol + 3 molecules of fatty acids joined together by ester bonds (strong covalent bonds)
• how are triglycerides formed + broken down


  formed by a condensation reaction, broken apart by hydrolysis
• how many different fatty acids are there


  over 70
• what molecules are involved in forming a triglyceride


  H from the glycerol and the OH from the fatty acid
• what causes variation between triglycerides


  variations in the fatty acid 'R' group
• what is the fatty acid 'R' group usually


  a long hydrocarbon chain
• what does it mean if hydrochain chain contains a C=C double bond


  it bends

  = its unsaturated

  = eg. oleic acid
• what does it mean if the chain is saturated


  full of carbon atoms so no double bond

  = eg. stearic acid
• characteristics of unsaturated fatty acids


  low melting point as the molecules cannot pack as tightly together

  = takes less energy to break bonds
• monounsaturated fatty acids


  1 double bond (C=C)

  = polyunsaturated have less than 1
• why do unsaturated fatty acids have a low melting point


  molecules cannot pack as tightly together
• Triglyceride structure and function (7)


  1. high ratio C-H to C atoms

  = effective energy source as easily oxidised

  
  

  2. insoluble in water

  = good energy store, doesn't affect water water potential

  = can be used for waterproofing eg. waxy cuticle in plants + insects

  
  

  3. compact structure

  = fats are a good long term energy store as contain more energy than carbohydrates

  = important in animals as less mass to carry as move

  
  

  4. slow conductor of heat

  = insulation eg. blubber in marine animals

  = electrical insulation, myelin sheath surrounding nerve cells

  = speeds up transmission of nerve impulse

  
  

  5. absorb 'shock' impact

  = protection eg. around delicate organs like the kidney

  
  

  6. high ratio H to O atoms (release water when oxidised)

  = metabolic source of water which is important for desert animals eg. camels can release H2O form triglycerides stored in humps

  
  

  7. less dense than water

  = buoyancy (marine mammals)

  = more efficient so less energy to stay afloat
• are phosphate molecules hydrophobic or hydrophilic

  hydrophilic
• what parts phospholipid made of

  - a hydrophilic head which interacts with water

  - a hydrophobic tail which orients itself away from water