1.5 lipids

Question 1

What characteristics do all lipids share?

Answer 1

• they contain carbon, hydrogen and oxygen
• proportion of oxygen to carbon atoms is smaller than in carbohydrates
• insoluble in water
• soluble in organic solvents (alcohols, acetone)

Question 2

What are the roles of lipids?

Answer 2

CELL MEMBRANES- phospholipids contribute to the flexibility of cell membranes and the transfer of lipid soluble substances across them.
ENERGY SOURCE- when oxidised lipids produce 2x the energy of carbohydrates and release water.
WATERPROOFING- as they are insoluble in water.
INSULATION- Fats are whslow conductors so they help retain body heat. they also provideelectrical insulation around nerve cells.
PROTECTION- Fat is often stored around delicate organs.

Question 3

Describe a triglyceride.

Answer 3

• three fatty acids combined with glycerol

- each fatty acid forms an ester bond with glycerol in a condensation reaction

Question 4

What causes differences in properties of fats and oils (triglycerides)?

Answer 4

• differences come from variation in fatty acids
• saturated fatty acids have no carbon double bonds and are solid at room temperature
• saturated fatty acids have carbon double bonds, and are liquid at room temperature, they can be:
  mono-unsaturated- one double bond
  poly-unsaturated- more than one double bond

Question 5

how does the structure of triglycerides relate to their properties?

Answer 5

• high ratio of energy-storing carbon-hydrogen bonds to carbon atoms which makes them a good energy source.
• low mass to energy ratio, making them good storage molecules.
• being large, non-polar molecules which are insoluble in water means they do not effect water potential in cells
• high ration of H to O atoms so release an important source o water when oxidised

Question 6

describe a phospholipid

Answer 6

• same structure as a lipid molecule, bu with a phosphate group rather than one of the fatty acid tails.
• polar molecule:
  HYDROPHILIC HEAD- phosphate molecule interacts with water but not fat
  HYDROPHOBIC TAIL- fatty acids interact with fat but not water

Question 7

How does the structure of phospholipids relate to their properties?

Answer 7

• they are polar molecules, so in an aqueous solution they form a bilayer, making a hydrophobic barrier between the inside and outside of the cell.
• hydrophilic head helps to hold the surface of the cell mebrane
• structure allows them to form glycolipids by combining with carbohydrates, which are important for cell recognition.

Question 8

Describe the emulsion test for lipids.

Answer 8

1) put 2cm3 of the sample with 5cm3 of ethanol in a test tube.
2) shake thoroughly to disolve any lipid in sample
3) add 5cm3 of water and shake gently
4) a cloudy-white colour ndicates the presence of a lipid
5) as a control, repeat using water, and the solution should remain clear.