Lipids

Question 1

What are the main classes of lipids?

Answer 1

Fatty acids, glycerol-based lipids, sphingosine-based lipids, steroids, terpenoids, lipopolysaccharides, and lipoproteins

Question 2

What is the structure of a fatty acid?

Answer 2

Long hydrocarbon tail (nonpolar) with a carboxyl group (COOH) at one end.

Question 3

What is the typical length of fatty acids in biological systems?

Answer 3

12–18 carbon atoms

Question 4

What affects the melting point of fatty acids?

Answer 4

Chain length and degree of saturation.

Question 5

What is the pKa of fatty acids?

Answer 5

Usually between 4.7 and 5.0.

Question 6

What are the two fatty acid numbering systems

Answer 6

Systematic (C1 = COOH group) and alternative (n-numbering from methyl end).

Question 7

What is the most common saturated fatty acid?

Answer 7

Palmitic acid (16:0).

Question 8

What is the most common monounsaturated fatty acid?

Answer 8

Oleic acid (18:1, cis-9 or n-9).

Question 9

What are essential fatty acids?

Answer 9

Alpha-linolenic acid, linoleic acid, and arachidonic acid (conditionally essential).

Question 10

Why are some fatty acids essential?

Answer 10

Humans cannot insert double bonds beyond the n-9 carbon.

Question 11

What are triacylglycerols composed of?

Answer 11

Glycerol backbone with three fatty acid chains.

Question 12

What is the physical state of saturated and unsaturated TAGs at room temp?

Answer 12

Saturated = solid (e.g., butter), Unsaturated = liquid (e.g., vegetable oil).

Question 13

What are simple TAGs?

Answer 13

TAGs with identical fatty acid chains.

Question 14

What are mixed TAGs?

Answer 14

TAGs with different fatty acids named by their position on glycerol.

Question 15

What is the energy yield of fatty acid oxidation vs. carbohydrates?

Answer 15

FA = 38 kJ/g; Carbs = 17 kJ/g.

Question 16

Why are TAGs efficient for energy storage?

Answer 16

High energy yield and low water content.

Question 17

Ideal omega-6:omega-3 ratio in diet?

Answer 17

2–4:1 (modern diet is about 15:1).

Question 18

Functions of TAGs?

Answer 18

Energy storage, insulation, protection

Question 19

What are phosphoglycerides?

Answer 19

Glycerol with two fatty acids and a phosphate group (may have additional groups like choline).

Question 20

Are phospholipids amphiphilic

Answer 20

Yes.

Question 21

Examples of common head groups in phospholipids?

Answer 21

Phosphatidylinositol, phosphatidylserine, phosphatidylcholine, ethanolamine.

Question 22

What backbone do sphingolipids use instead of glycerol?

Answer 22

Sphingosine (an amino alcohol).

Question 23

What is a ceramide?

Answer 23

Sphingosine with a fatty acid via the amino group

Question 24

What is sphingomyelin?

Answer 24

A sphingolipid with phosphorylcholine; 25% of human lipids.

Question 25

Role of sphingomyelin in the body?

Answer 25

Forms myelin sheath, stabilizes membranes, alters fluidity

Question 26

What are glycolipids composed of?

Answer 26

Lipid + carbohydrate (e.g., glucose or galactose).

Question 27

Where are glycolipids commonly found?

Answer 27

Nervous system, plant cells

Question 28

Functions of glycolipids

Answer 28

Membrane structure, cell recognition (e.g., blood groups).

Question 29

What is the basic structure of steroids?

Answer 29

Four fused rings (3 six-membered, 1 five-membered).

Question 30

Where are steroids found?

Answer 30

Only in eukaryotes.

Question 31

What is the most common steroid?

Answer 31

Cholesterol.

Question 32

What are hopanoids?

Answer 32

Steroid-like molecules in prokaryotes.

Question 33

Cholesterol functions in membranes?

Answer 33

Stabilizes at high temp, increases fluidity at low temp.

Question 34

What is cholesterol a precursor for?

Answer 34

Sex hormones, vitamin D, bile salts, corticosteroids.

Question 35

List some hormones derived from cholesterol

Answer 35

Testosterone, progesterone, cortisol, aldosterone.

Question 36

What are bile salts derived from?

Answer 36

Cholesterol (e.g., taurocholate).

Question 37

What are terpenoids synthesized from?

Answer 37

IPP (isopentenyl diphosphate) and DMAPP.

Question 38

Name some important terpenoid products.

Answer 38

Vitamin A, Vitamin K, ubiquinone (CoQ10)

Question 39

What are lipoproteins?

Answer 39

Complexes of lipids and proteins for FA transport (HDL, LDL, etc.).

Question 40

What are lipopolysaccharides?

Answer 40

Lipid + carbohydrate molecules (e.g., in bacterial outer membranes).

Question 41

What are waxes?

Answer 41

Esters of long-chain alcohols and fatty acids; water-repellent