Tutorial 13 — Lipids

Note: This tutorial PDF consists primarily of scanned images. The questions below are reconstructed based on typical FAD1018 Tutorial 13 content on Lipids.

Tutorial Information

Extracted note: "Dr Danial" — possibly the lecturer's name

Learning Outcomes

Classify lipids (fats, oils, phospholipids, steroids, waxes)
Understand fatty acid structure and properties
Learn lipid reactions (hydrolysis, hydrogenation, saponification)
Understand membrane lipids and their functions
Know the structure and function of steroids

Part A: Fatty Acids

Question 1

a) Define fatty acid. What is the general structure?

b) Classify fatty acids based on:

Chain length (short, medium, long)
Saturation (saturated, unsaturated)

c) Give examples of:

Saturated fatty acid (palmitic acid, stearic acid)
Monounsaturated fatty acid (oleic acid)
Polyunsaturated fatty acid (linoleic acid, linolenic acid)

Question 2

a) Write the structure of:

Palmitic acid (16:0)
Stearic acid (18:0)
Oleic acid (18:1, cis-Δ⁹)
Linoleic acid (18:2, cis,cis-Δ⁹,¹²)

b) Explain the notation 18:2, cis,cis-Δ⁹,¹².

c) What is the difference between cis and trans fatty acids?

Question 3

a) Why do unsaturated fatty acids have lower melting points than saturated fatty acids?

b) Arrange the following in order of increasing melting point:

Stearic acid
Oleic acid
Linoleic acid
Palmitic acid

c) Explain why fats are solid at room temperature while oils are liquid.

Part B: Triglycerides (Fats and Oils)

Question 4

a) What is a triglyceride (triacylglycerol)?

b) Draw the general structure of a triglyceride formed from glycerol and three fatty acids.

c) What is the difference between fats and oils?

Question 5

a) Write the equation for the hydrolysis of a triglyceride.

b) What is saponification? Write the reaction for the saponification of tristearin with NaOH.

c) What products are formed?

Question 6

a) What is hydrogenation of oils? Write a representative equation.

b) Why is vegetable oil hydrogenated commercially?

c) What are the health concerns associated with trans fats?

Part C: Phospholipids

Question 7

a) What is a phospholipid? Draw the general structure.

b) Compare phosphoglycerides and sphingolipids.

c) What is the role of phospholipids in cell membranes?

Question 8

a) Draw the structure of phosphatidylcholine (lecithin).

b) Identify the hydrophilic and hydrophobic parts.

c) Explain how phospholipids form lipid bilayers.

d) Why are phospholipids described as amphipathic?

Part D: Waxes and Steroids

Question 9

a) What are waxes? Give examples and their uses.

b) Write the general structure of a wax ester.

c) Why are waxes water-resistant?

Question 10

a) What is the basic structure of steroids?

b) Draw the steroid nucleus (cyclopentanoperhydrophenanthrene ring system).

c) Identify the following steroids and their functions:

Cholesterol
Testosterone
Estradiol
Cortisol
Bile acids

Part E: Lipid Reactions and Analysis

Question 11

a) What is the iodine number? How is it determined?

b) Calculate the iodine number for triolein.

c) What does a high iodine number indicate?

Question 12

a) What is the acid value of a fat or oil?

b) What does a high acid value indicate about the quality of an oil?

c) How is rancidity developed in fats and oils?

Question 13

a) What is the saponification value?

b) Calculate the saponification value for tristearin (MW = 891.5 g/mol).

c) What information does the saponification value provide?

Key Concepts

Fatty Acid — Long-chain carboxylic acid
Triglyceride — Ester of glycerol with three fatty acids
Phospholipid — Lipid containing phosphate group
Sphingolipid — Lipid based on sphingosine backbone
Steroid — Lipid with four fused rings
Saponification — Base-catalyzed hydrolysis of esters
Hydrogenation — Addition of hydrogen to double bonds
Iodine Number — Measure of unsaturation
Saponification Value — Measure of average molecular weight
Amphipathic — Having both hydrophilic and hydrophobic parts

Summary Table: Lipid Types

Lipid Type	Structure	Function/Example
Fatty acids	Long-chain R-COOH	Building blocks
Triglycerides	Glycerol + 3 fatty acids	Energy storage
Phospholipids	Glycerol + 2 fatty acids + phosphate	Membranes
Waxes	Long-chain alcohol + fatty acid	Protection
Steroids	Four fused rings	Hormones

FAD1018 Tutorial 13 — Lipids