1. Give some differences between a triglyceride and a phospholipid.
Answer
Triglyceride contains three fatty acid chains, while phospholipid only contains two. Triglyceride is non polar, while phospholipid is polar. Triglyceride is hydrophobic, while phospholipid has a hydrophilic head and hydrophobic tail.
2. A fatty acid can be represented by the formula R-COOH. What does the letter R represent ?
Answer
The variable region of the fatty acid, which is the hydrocarbon chain.
3. Identify which of the two fatty acids shown below is saturated. Explain your answer.
Answer
Fatty acid A because it has no C=C bonds.
4. Olestra is a fat substitute. It is made from a molecule of sucrose with fatty acids attached. Its structure is shown in the figure below. "X" represents the positions where fatty acids are attached. Name the bond at position Y.
Answer
Glycosidic bond.
5. Olestra is not digested in the gut. Explain why.
Answer
Olestra has a different shape from normal sucrose or lipids, so it does not fit into the active site of digestive enzymes such as lipase or sucrase.
6. Describe a test you could carry out to show that biscuits have lipids present.
Answer
Grind and mix with alcohol. Add equal volume of water, shake and positive result is a white emulsion.
7. Draw a phospholipid molecule and label it to explain why it can be called a polar molecule.
Answer
8. What is the key difference between lipids (fats) and carbohydrates ?
a) molecular size
b) amount of carbon
c) presence of closed rings versus open chains
d) amount of oxygen
Answer
d) amount of oxygen
9. Which of the following formulae represents a lipid ?
a) C12H22O11 b) NH4NO3 c) C57H116O6 d) CH3COCOOH
Answer
c) C57H116O6
10. Which of the following statements about lipids is correct ?
a) triglycerides are formed by ester bonds between glycerol and three fatty acids
b) phospholipids contain a hydrophilic phosphate group and hydrophobic fatty acid tails
c) saturated fatty acids contain double bonds that introduce kinks into the hydrocarbon chain
d) lipids are generally insoluble in water but soluble in organic solvents
Answer
c) saturated fatty acids contain double bonds that introduce kinks into the hydrocarbon chain