Lipids

Question 1

Role of Lipids in biology

Answer 1

Store of energy for producing ATP in respiration.
Insulation.
Protection.
Waterproofing e.g. waxy cuticles of leaves.
Production of phospholipids for formation of cell surface / organelle membranes.

Question 2

Saturated fatty acid

Answer 2

fatty acids have only C-C (no double bonds between the carbon atoms) so form linear hydrocarbon chains.
Fatty acid chains only have C-C bonds and are straight (stearic).
Triglycerides pack closely together and stick more strongly.
Higher melting point.
Solid at room temperature.

Question 3

Unsaturated fatty acid

Answer 3

fatty acids have one or more C=C which causes the hydrocarbon chain to bend.
Fatty acid chains have C=C bonds and are non-linear / bent.
Triglycerides don’t pack closely together and stick less strongly.
Lower melting point.
Liquid at room temperature.

Question 4

formation of a triglyceride

Answer 4

One glycerol bonds with 3 fatty acids.
Condensation reaction releasing 3 water molecules.
Ester bonds form.
Between hydroxyl groups (-OH) on the glycerol and carboxylic groups on fatty acids (-COOH)

Question 5

food test for lipids.

Answer 5

If the sample is solid then grind it.

Add 2cm3 of ethanol / alcohol and shake.

then…

Add 2cm3 of water (shake)

Colour change from clear to white / milky emulsion

Question 6

Formation of a Phospholipid

Answer 6

One glycerol bonds with 2 fatty acids and one phosphate group. Condensation reaction release three water molecules and forms an ester bond.
Hydrophilic head, hydrophobic tail

Question 7

Describe the formation of a phospholipid bilayer.

Answer 7

Hydrophilic, phosphate heads face outwards, attracted to water..

Both inside and outside of the cell.

Hydrophobic fatty acid tails turn inwards, repelled by water.

Question 8

Explain the roles of phospholipid bilayers in the cell surface membrane.

Answer 8

Boundary between a cell’s cytoplasm and the external environment.
Different conditions inside the cell.

Partially controls the movement of substances in and out of the cell.
Non-polar / lipid soluble molecules can diffuse directly through the bilayer.
Hydrophilic / polar / charged molecules require protein transport channels.

Question 9

Explain the roles of phospholipid bilayers in organelle membranes.

Answer 9

Control entry / exit of substances.
Separate organelle contents from cytoplasm to allow specific metabolic reactions e.g. mitochondrial matrix and Kreb’s cycle
Isolate enzymes e.g. lysosomes and hydrolytic enzymes.
Provide a surface for biochemistry e.g. thylakoids and the LDR