Lipids

• what percentage of a cell do lipids make up?


  5 %
• what is the difference between a fat and an oil?

  fats are lipids that are solids at room temperature and oils are lipids that are liquid at room temperature
• what are the functions of lipids in living organisms?

  • membrane formation and the creation of hydrophobic barrier
  • hormone production
  • electrical insulation necessary for impulse transmission
  • waterproofing - birds feathers and on plants leaves
  • thermal insulation to reduce heat loss
  • cushioning to protect vital organs like the heart and kidney
  • buoyancy for aquatic animals like whales
• what are the components of a lipid?

  glycerol and fatty acids
• how is a triglyceride formed?

  the lipid goes through a condensation reaction (water is removed) and ester bonds between the glycerol and the fatty acids are formed, forming a triglyceride
• what is a saturated fat?

  fatty acid chains that have no double bond present between the carbon atoms, all the carbon atoms form the maximum number of bonds with the H atoms
• what lengths are fatty acid hydrocarbon chains?

  can vary from 10-30 carbons, most commonly 12-18 carbons
• what is a monounsaturated fatty acid?

  A fatty acid with one double bond between carbon atoms
• what is a polyunsaturated fatty acid?

  A fatty acid with more than one double bond between carbon atoms
• how does the shape of an unsaturated fatty acids differ to a saturated fatty acid?

  the presence of a double bond in an unsaturated fatty acid causes the molecule to kink or bend so it cannot pack closely together. Saturated fatty acids can pack closely together.
• how does the number of double bonds affect membrane fluidity?

  the presence of a double bond causes a kink in the chain which makes it harder for hydrocarbons to pack closely together, increasing membrane fluidity
• how does the number of double bonds affect the melting point?

  decreases the melting point
• how is a glycerol molecule and a fatty acid molecule formed from a monoglyceride molecule?

  a hydrolysis reaction, the ester bond is broken and a water molecule is used up
• how is a monoglyceride molecule formed from a glycerol molecule and a fatty acid molecule?

  a condensation reaction, esterfication occurs (ester bond made), and a water molecule is eliminated
• when is a triglyceride molecule formed?

  when three fatty acids are covalently bonded to a glycerol molecule
• why are triglycerides not considered to be polymers?

  they are made of more that one type of unique substance, they are not a true repeating subunit
• what is the word equation for the hydrolysis of a triglyceride?

  triglyceride + 3 water = 3 fatty acids + glycerol
• how are triglycerides used as an energy source?

  when bonds are broken, energy is released (more energy is released than taken in), there are also large amounts of C-H bonds which have a high energy density
• why are triglycerides good storage molecules?

  they are fluid so don't take up much space (are relatively light), are insoluble so wont affect the water potential of cells
• why do saturated and unsaturated fats have different melting points?

  • Saturated - fats (which are less fluid) and have a more stable structure (C-C), have a higher m.p.
  • Unsaturated - oils (more fluid) and have kinks and bends due to C=C, oils can't be closely packed, so have lower m.p. due to weaker intermolecular forces
• define hydrophilic

  • a charged or polar molecule that can interact with water molecules (often by forming hydrogen bonds) and are therefore soluble in water
• define hydrophobic

  • a non-polar molecule that cannot interact with water molecules and is therefore insoluble
• define phosphate group

  • an inorganic group containing phosphorus and oxygen
• define glycerol

  • an organic molecule, which is a component of triglycerides and phospholipids
• define ester bonds

  • a bond between glycerol and a fatty acid
• define ester

  • a group where one O atom is doubly bonded to a C atom which is singly bonded to another O atom, which is again slightly bonded to another C atom
• compare triglycerides and phospholipids

  • both contain glycerol
  • both contain some ester bonds
  • both contain some fatty acids
  • phospholipid has a phosphate group and a triglyceride doesn't
  • triglyceride has 3 fatty acids and phospholipid has 2
  • triglyceride has 3 ester bonds and phospholipid only has 2
  • triglyceride is non-polar whereas phospholipid is amphipatic
• why are phospholipids known as surfactants?

  when they interact with water they will form a layer on the water surface, with the phosphate heads in the water and the fatty acid tails sticking out of the water
• what is the role of surfactants in alveoli?

  coats the alveoli and lowers the surface tension of water - prevents alveoli from collapsing after exhalation and makes breathing easy
• what is meant by the term sterol?

  a type of liquid, a complex alcohol molecule, based on a four carbon ring structure with a hydroxyl (OH) group at one end

  • they have dual hydrophilic/hydrophobic characteristics
• how does cholesterols structure help with its function?

  • hydrophilic HO group on head meaning it can interact with the phospholipid head
  • hydrophobic body with can interact with phospholipid tails