1.3 Lipids

Question 1

Name two groups of lipids.

Answer 1

Triglycerides and Phospholipids

Question 2

What bond is found in a lipid?

Answer 2

A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.

Question 3

What is a triglyceride?

Answer 3

Formed by the condensation of one molecule of glycerol and three molecules of fatty acid.

Question 4

What is a phospholipid?

Answer 4

Formed by the condensation of one molecule of
glycerol, two molecules of fatty acid and one phosphate-containing group.

Question 5

The R-group of a fatty acid can be … or …

Answer 5

saturated (contains only single bonds) or unsaturated (contains double and or triple bonds)

Question 6

Test for lipids

Answer 6

Emulsion Test:
1. Put food sample in a test tube (if solid grind up the sample using a pestle and mortar).
2. Add a few drops of ethanol to the test tube and shake.
3. Pour the contents of the test tube into a test tube of water.
+VE result: milky emulsion will form

Question 7

Properties and functions of triglyceride

Answer 7

• Large non-polar molecules: doesn’t affect water potential
• High ratio of C-H:C atoms: excellent source of energy
• Low mass:energy ratio lots can be stored in a small volume and reduces mass
• High ratio of H:O: water is released when oxidised

Question 8

Function of triglycerides.

Answer 8

1. Energy Storage → the long hydrocarbon chains contain many carbon-hydrogen bonds with little oxygen, so when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP. Therefore, they store more energy per gram than carbohydrates and proteins. Furthermore triglycerides are hydrophobic so do not effect the water potential of cells so more energy can be stored. Also releases large amounts of water molecules (desert animals retain this water if there is no liquid water and birds and reptile embryos use this water in their shells)
2. Insulation → triglycerides are part of the composition of the myelin sheath that surrounds nerve fibres which provides insulation increasing the speed of transmission of nerve impulses. Triglycerides also compose part of the adipose tissue layer below the skin which acts as insulation against heat loss
3. Buoyancy → the low density of fat tissue increases the ability of animals to float more easily
4. Protection → the adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage

Question 9

Function of phospholipids.

Answer 9

1. The main component (building block) of cell membranes.
2. Due to the presence of hydrophobic fatty acid tails, a hydrophobic core is created when a phospholipid bilayer forms which acts as a barrier to water-soluble molecules.
3. The hydrophilic phosphate heads form H-bonds with water allowing the cell membrane to be used to compartmentalise, this enables the cells to organise specific roles into organelles helping with efficiency.
4. Composition of phospholipids contributes to the fluidity of the cell membrane. (Mainly saturated fatty acid tails → less fluid)
5. Phospholipids control membrane protein orientation as weak hydrophobic interactions between the phospholipids and membrane proteins hold the proteins within the membrane but still allow movement within the layer.

Question 10

Structure of phospholipids.

Answer 10

• phosphate head (hydrophilic and polar)
• hydrophobic fatty acid tails (non-polar)