Lipids

Question 1

What is the r group for fatty acods

Answer 1

Hydrocarbon chain

Question 2

Describe two differences between the structure of the triglyceride shown in Figure 2 and a phospholipid.

Answer 2

Triglyceride has 3 fatty acids rather than 2;
3 ester bonds rather than 2;

3. No phosphate group;

Question 3

(c) Explain why phospholipids can form a bilayer but triglycerides cannot.

Answer 3

Phospholipid both hydrophobic and hydrophilic
OR
Phospholipid polar
OR
Phosphate group is charged;

2. Triglycerides only hydrophobic

. Fatty acid/triglyceride is non-polar;
Accept ‘Triglycerides not hydrophilic’
3. Hydrophilic/phosphate group attracts water (to either side of
bilayer);

Question 4

What do unsaturated fatty acids cause

Answer 4

Cause kink / bends in fatty acid tail
Which leads to increased fluidity

( in cell membranes it make the membrane more fluid / flexible )

Question 5

Describe the hydrolysis reactions involved in the digestion of triglycerides.

Answer 5

Breaking of ester bonds
Addition of water

Question 6

(d) The ratio of saturated to unsaturated fatty acids in a cell-surface membrane determines the extent of the membrane’s fluidity.
Scientists provided a cell culture of mouse phagocytes with liquid broth rich in unsaturated fatty acids.
The scientists observed:
• an increase in the proportion of phospholipids in the phagocytes containing unsaturated fatty acids
• more phagocytosis.
Suggest and explain why there was more phagocytosis.

Answer 6

More unsaturated fatty acids increases fluidity (in (cell-surface
membrane);
2. (Making cell-surface) membrane more fluid/ flexible;
3. Easy to engulf;

Question 7

Which enzymes hydrolyses lipids

Answer 7

Lipase

Into fatty acids and glycerol