Lipids

• What are the 2 parts that make up a carboxylic acid

  carboxyl group + hydrocarbon chain
• Lipids provide more than twice the amount of energy as carbohydrates
• Where do plants store fats or oils?

  seeds
• Where do mammals store fats?

  Specialised cells called adipocytes, which contain fat globules
• What are the 2 functions of lipids and why is it important?


  . heat insulation- in mammals, adipose tissue underneath the skin helps to reduce heat loss

  . Protection- adipose tissue around delicate organs acts as a cushion against impacts
• Name the three most common elements in lipids

  carbon, hydrogen and oxygen
• What are the 3 main examples of lipids

  triglycerides

  phospholipids

  cholesterol
• What 2 main components do triglycerides and phospholipid molecules both share

  glycerol and fatty acids
• Describe the structure of glycerol


  An organic compound with three carbons and three hydroxyl (OH) groups

  each -OH group is able to form an ester bond with a fatty acid
• Describe the structure of fatty acids


  a long chain of hydrocarbons to which a carboxyl group is attached
• What is the general formula of a saturated fatty acid

  CnH(2n+1)COOH
• How would you tell if a fatty acid is saturated?

  if there are only single bonds between neighbouring carbons in the hydrocarbon chain
• How would you tell if a fatty acid is unsaturated?

  when the hydrocarbon chain contains a double bond
• What do the double bonds between fatty acid chains cause, and why does this mean they have a lower melting point?

  to bend and kink, because of this the fatty acid chains don't pack together as uniformly so less energy is required to overcome intermolecular forces
• Why do saturated fats have a higher melting point?

  they pack together because of the single bonds so more energy is required to break the intermolecular force
• Saturated fats are solids at room temperature
• unsaturated fats are liquid in room temperature
• Define esterification


  A condensation reaction making an ester bond
• Both triglycerides and phospholipids are made via the formation of an ester bond between each fatty acid and the glycerol molecule
• Describe the structure of triglycerides

  Triglycerides contain three fatty acid molecules attached to one molecule of glycerol. The fatty acid molecules are made of hydrocarbons but each tail can vary in length
• Describe 2 similarities and one difference between phospholipids and sterols

  Similarities-> Both have hydrophilic/hydrophobic characteristics and make up the plasma membrane

  Differences-> sterols are complex alcohol molecules whereas phospholipids are lipids
• Describe the function of triglycerides

  used as an energy store

  energy is released when ester bonds are hydrolysed

  group together in lipid droplets that make good energy storage molecules since they do not affect the osmotic potential
• Describe the structure of phospholipids

  an amphipathic molecule so it has a hydrophobic part and a hydrophilic part

  tails are fatty acid chains that are hydrophobic and repel water

  the head is hydrophilic and attracts water
• Describe how phospholipids are structured in a membrane

  In a membrane a bilayer of phospholipids forms as the phospholipids' fatty acid tails face inwards, away from water whereas the phosphate group faces the outside towards the cytoplasm and extracellular which are aqueous
• Describe the function of phospholipids


  The phospholipids bilayer forms a barrier preventing any large polar molecules from entering or leaving the cell

  If a drop of phospholipids is placed in water, it spontaneously forms a structure called a micelle where the hydrophilic phosphate heads face the outside and the fatty acids face the structure's interior
• Describe the structure of cholesterol

  contains hydrocarbon steroid rings, hydrocarbon chain and a polar hydroxyl group
• What is cholesterol used for

  to synthesise bile and steroid hormones
• Describe the role of cholesterol in the plasma membrane and how are they grouped together, how do they react in water


  They are grouped together as they are also hydrophobic and insoluble in water. Cholesterol between the hydrophobic tails of phospholipids in plasma membranes and contributes to membrane fluidity