L4 - lipids

• Lipids can be oils or fats:

  -oils are liquid at room temperature and are more present in plants

  -fats are solid at room temperature and are more present in animals
• Lipids:

  -contain carbon, hydrogen and oxygen (unlike carbs however, lipids have a lot less oxygen)

  -lipids are non polar molecules so are insoluble in water

  -soluble in organic solvents

  -generally water hating (hydrophobic)

  -building blocks are fatty acids and glycerol

  -do not form polymers
• Lipids:

  -triglycerides (fats and oils)

  -phospholipids

  -other lipids (steroids, hormones, cholesterol, waxes)
• Each lipid has its own range of lipids and each one has its own function depending on the structure. Some general functions include:

  -energy storage

  -metabolic water source

  -membrane structure

  -water proofing

  -insulation

  -hormones
• Lipids with fatty acids:

  -triglycerides

  -phospholipids

  -waxes
• Lipids without fatty acids:

  -steroids

  -cholesterol
• Fatty acid chains:

  -consists of a long chain or carbons and hydrogens with a carboxyl at one end
• Saturated fatty acids: the hydrocarbon chain has only single bonds
• Unsaturated fatty acids: the hydrocarbon chain consists of at least one double bond
• Saturated fatty acid

  
• Unsaturated fatty acid

  
• Unsaturated fats:

  -can be cis or trans

  -this refers to the arrangement of the two hydrogen atoms bonded to the atoms involved in a double bond

  -in the cis arrangement, the hydrogens are on the same side of the double bond

  -in the trans arrangement, the hydrogens are on opposite sides of the double bonds

  
• A saturated fatty acid has a very regular shape. They have no double bonds between carbon atoms. They tend to be solid at normal room temperatures
• A mono-unsaturated fatty acid only has one bend. These have double bonds. They have a low melting point and so tend to be liquid at room temperatures
• A poly-unsaturated fatty acid is very bent and irregular. It has lots of double carbon bonds causing the bending
• Unsaturated fats:

  -the presence of double bonds causes kinks in the fatty acid chains

  -this irregular shape makes the molecules in the lipid push apart and unable to pack close together (making them more fluid)

  -due to this unsaturated triglycerides have a low melting point and tend to be liquid oils as room temperature (present more in plants)
• Glycerol:

  -one of the building blocks in lipids

  -a 3 carbon alcohol (contains 3 hydroxyl groups)

  -always the same

  
• One molecule of glycerol and one fatty acid bonded together make a monoglyceride and water. These are joined by ester bonds
• Triglyceride formation:

  -the reactions between the fatty acids and glycerol are condensation reactions

  -glycerine molecule is always the same but the fatty acids vary

  -condensation reaction always occurs between carboxyl group (COOH) of fatty acid and hydroxyl group (OH) of the glycerol

  -ester bonds form

  -hydrocarbon tail can be saturated or unsaturated and vary in length

  -hydrophobic as no spare oxygen molecules for water to form hydrogen bonds with
• Triglycerides:

  -made from one molecule of glycerol and 3 fatty acids

  -fatty acids are hydrophobic
• Respiration of lipids:

  -requires the hydrolysis of ester bonds in triglycerides

  -lipids can be broken down completely to carbon dioxide and water

  -this hydrolysis releases energy which is used to generate ATP molecules

  -lipid respirations releases twice as much energy as carbohydrates and also more water. Due to this, some organisms use stored fat as a water supply
• A hydrolysis reaction will break the ester bond between glycerol and a fatty acid as it adds water
• Triglyceride properties:

  -good energy storage molecule. This is because long fatty acid tails contain lots of chemical energy

  -insoluble in water (so doesn’t affect water potential). Fatty acid tails are hydrophobic so they shield themselves from water by bundling together in droplets
• Lipids:

  -energy source and metabolic water source

  -fat as a buoyancy aid (fat is stored as adipose tissue. in aquatic animals it’s called blubber and used as a buoyancy aid as fat is less dense than muscle or bone)

  -heat insulation

  -waterproofing on hair and feathers

  -electrical insulation in Schwann cells