lipids

• What are the elements of lipids?

  C, H, O
• Are lipids insoluble or soluble in water and why?

  insoluble - the fatty acids are hydrophobic so are insoluble
• what is the general formula of a fatty acid?

  R-COOH
• what can lipids dissolve in?

  organic solvents e.g. acetone and alcohols
• what are the 2 types of lipids?

  fats and oils
• what's the difference between fats and oils?

  fats are solid at room temp and oils are liquid at room temp
• what are triglycerides made up of?

  glycerol and 3 fatty acids
• How is a triglyceride formed?

  each hydroxyl group on the glycerol forms an ester bond with a separate fatty acid in a condensation reaction
• what is the reaction called when fatty acids form bonds with glycerol?

  esterification
• where does the H2O molecule come from in the formation of an ester bond?

  the hydroxyl group comes from the fatty acid and the hydrogen comes from the glycerol
• what is the difference between a saturated and an unsaturated fatty acid?

  unsaturated = one or more double bonds in the carbon chain. saturated = no double bonds
• what is the difference between a monounsaturated and a polyunsaturated fatty acid?

  mono = one double bond

  poly = two or more double bonds
• which is more fluid, saturated, or unsaturated and why?

  unsaturated because the other fatty acids are pushed apart by the double bonds
• Why aren't triglycerides polymers?

  they don't have repeating units
• What are phospholipids?

  one of the fatty acids is replaced by phosphoric acid
• describe the structure of phospholipids?

  polar phosphate heads made up of the phosphate group and glycerol with one saturated and one unsaturated fatty acid
• what are the hydrophobic and hydrophilic parts of phospholipids and how do they behave in water?

  the phosphate head is hydrophilic and the fatty acids are hydrophobic. The phosphate head stays in the water and the two fatty acids point out of the water
• what is the membrane made up of phospholipids called?

  the fluid-mosaic model
• what does the phosholipid membrane consist of?

  double layer of phospholipids - called the phospholipid bilayer
• why doesn't the cell membrane dissolve in water?

  phospholipids are insoluble
• what is cholesterol

  a sterol alcohol (lipid)
• what are sterols?

  lipids with a 4 carbon ring structure with one hydroxyl group
• describe the polarity of sterols?

  the OH is polar and the rest of the molecule is non-polar
• what is cholesterol's function and how does it do this?

  regulates the membrane's fluidity by fitting in between the fatty acid tails so they phospholipids don't come together in a regular solid structure
• what property of cholesterol allows it to carry out its function?

  it's small and flat so it can fit between the phospholipids
• How does cholesterol affect membrane fluidity?

  • at higher temperatures, they bind to the hydrophobic tails of phospholipids, causing them to pack more closely together = less fluid
  • at lower temperatures, cholesterol prevents phospholipids from packing too close together and so increases membrane fluidity
• what is cholesterol used to make?

  steroid hormones: oestrogen, testosterone, vitamin D and cortisone
• why is a high cholesterol level dangerous?

  it can cause fatty deposits to build up in the arteries, restricting the blood flow to the heart or brain, causing heart attacks or strokes
• why are lipids good energy sources?

  - they produce more ATP than glucose

  - they are insoluble so no effect on water potential

  - they have a low mass to energy ratio so small amounts release a lot of energy so only small volumes need to be stored
• why are lipids good thermal and electrical insulators?

  they conduct heat slowly - they are stored under the skin

  to retain body heat and as myelin sheath as electrical insulators
• what do aquatic animals use fat for?

  buoyancy - fat is less dense than water so it helps them to float