A4. Lipids

Question 1

What are lipids made from?
Lipids are different from proteins and carbohydrates because they’re not polymers formed from long chains of monomers. Lipids are made from a variety of different components, but they all contain __________________. The components they’re made from relates to the lipid’s function. There are two types of lipid you need to know about-_______________and _________________.

Answer 1

What are lipids made from?
Lipids are different from proteins and carbohydrates because they’re not polymers formed from long chains of monomers. Lipids are made from a variety of different components, but they all contain hydrocarbons. The components they’re made from relates to the lipid’s function. There are two types of lipid you need to know about-triglycerides and phospholipids.

Question 2

Triglycerides (2 things)

Answer 2

• one molecule of glycerol with three fatty acids attached to it.
• hydrophobic fatty acid tails that make it insoluble in water

Question 3

Fatty acids
All fatty acids consist of the same basic structure, but the hydrocarbon tail varies - see Figure 2. There are two kinds of fatty acids-saturated and unsaturated. The difference is in their hydrocarbon tails (_ _________)

Figure 2: Structure of a fatty acid

Answer 3

R Groups

Question 4

What is the difference between saturated and unsaturated fatty acids?

Answer 4

Unsaturated fatty acids do have double bonds between adjacent carbon atoms, which cause the chain to kink whereas saturated fatty acids have no double bond between adjacent carbons atoms

Question 5

Triglyceride formation
Figure 5 shows a fatty acid joining to a glycerol molecule. An _____ bond forms between the two molecules, releasing a molecule of water-this is a ________________reaction. This process happens twice more to form a triglyceride.

Figure 5: Triglyceride formation.

Tip: You can pretty much ignore the ‘R’ group on the fatty acid -it never gets involved in the reaction.

Answer 5

Figure 5 shows a fatty acid joining to a glycerol molecule. An ester bond forms between the two molecules, releasing a molecule of water-this is a condensation reaction. This process happens twice more to form a triglyceride.

Question 6

Phospholipids (4 things)

Figure 6: Structure of a phospholipid.

Answer 6

• one of the fatty acid molecules is replaced by a phosphate group.
• The phosphate group is hydrophilic (attracts water).
• The fatty acid tails are hydrophobic (repel water).
• This is important in the cell membrane as it forms a phospholipid bilayer

Question 7

Properties of lipids - Triglycerides (3 things)

Answer 7

• Triglycerides are mainly used as energy storage molecules. They’re good for this because the long hydrocarbon tails of the fatty acids contain lots of chemical energy
• They’re insoluble in water, so they don’t affect the water potential of the cell and cause water to enter the cells by osmosis
• The triglycerides bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic the tails face inwards, shielding themselves from water with their glycerol heads

Question 8

Properties of lipids - Phospholipids - Phospholipid Bilayer (3 things)

Answer 8

• Phospholipids make up the bilayer of cell membranes and it controls what enters and leaves a cell.
• Phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side.
• The centre of the bilayer is hydrophobic, so water-soluble substances can’t easily pass through it—the membrane acts as a barrier to those substances.

Question 9

Test for Lipids

Answer 9

1) Add ethanol to substance
2) Shake
3) Add water
4) Milky emulsion = lipid present