Lipids

Question 1

What are lipids?

Answer 1

Lipids are macromolecules made of carbon, hydrogen, and oxygen.

Question 2

What are examples of lipids?

Answer 2

Examples include fats, oils, phospholipids, and sterols.

Question 3

Are lipids polar or non-polar molecules?

Answer 3

Lipids are non-polar molecules.

Question 4

Why are lipids hydrophobic?

Answer 4

Lipids are hydrophobic because their bonds distribute electrons evenly, so they lack charged regions and do not dissolve in water.

Question 5

What are the physical states of lipids at room temperature?

Answer 5

Fats: Solid at room temperature.

Oils: Liquid at room temperature.

Question 6

Are lipids polymers?

Answer 6

No, lipids are macromolecules made from smaller monomers (like glycerol and fatty acids) but do not form repeating chains like polymers.

Question 7

What is a triglyceride?

Answer 7

A triglyceride is a lipid formed from one glycerol molecule and three fatty acids.

Question 8

What is the role of the carboxyl group in fatty acids?

Answer 8

The carboxyl group (-COOH) interacts with the hydroxyl group (-OH) of glycerol to form ester bonds.

Question 9

What type of reaction forms a triglyceride?

Answer 9

A condensation reaction (esterification), where three water molecules are removed to form three ester bonds.

Question 10

What happens during hydrolysis of triglycerides?

Answer 10

Hydrolysis uses water to break down triglycerides, reversing the esterification process and releasing glycerol and fatty acids.

Question 11

What is an ester bond?

Answer 11

An ester bond forms between the hydroxyl (-OH) group of glycerol and the carboxyl (-COOH) group of a fatty acid during esterification.

Question 12

What happens during esterification?

Answer 12

Esterification is a condensation reaction where three molecules of water are removed as glycerol bonds with three fatty acids to form a triglyceride.

Question 13

What defines a saturated fatty acid?

Answer 13

A saturated fatty acid has no double bonds between carbon atoms; all carbon atoms are fully saturated with hydrogen.

Question 14

What defines an unsaturated fatty acid?

Answer 14

An unsaturated fatty acid contains one or more double bonds between carbon atoms.

Question 15

How do double bonds affect the structure and properties of fatty acids?

Answer 15

Double bonds create kinks in the fatty acid chain, preventing close packing. This makes unsaturated fats liquid at room temperature.

Question 16

What are monounsaturated and polyunsaturated fatty acids?

Answer 16

Monounsaturated: One double bond.

Polyunsaturated: Two or more double bonds.

Question 17

Why are unsaturated fats considered healthier than saturated fats?

Answer 17

Unsaturated fats (found in plants and fish) are associated with a reduced risk of heart disease compared to saturated fats.

Question 18

What are the health risks associated with saturated fats?

Answer 18

Saturated fats are linked to coronary heart disease, though recent evidence is inconclusive.

Question 19

What are phospholipids made of?

Answer 19

Phospholipids consist of one glycerol molecule, two fatty acids, and a phosphate group.

Question 20

What is the hydrophilic region of a phospholipid?

Answer 20

The phosphate group is hydrophilic (water-attracting).

Question 21

What is the hydrophobic region of a phospholipid?

Answer 21

The fatty acid tails are hydrophobic (water-repelling).

Question 22

What is the structure of the phospholipid bilayer?

Answer 22

In water, phospholipids form a bilayer with hydrophilic heads facing outward and hydrophobic tails inward.

Question 23

Why is the phospholipid bilayer important in cells?

Answer 23

The bilayer structure forms cell membranes, separating the cell’s interior from its aqueous environment.

Question 24

What are sterols?

Answer 24

Sterols are complex lipid molecules with a four-ring structure and a hydroxyl (-OH) group.

Question 25

What is cholesterol, and where is it found?

Answer 25

Cholesterol is a sterol essential for cell membranes, making them stable and fluid.

Question 26

How does cholesterol maintain membrane stability?

Answer 26

Cholesterol prevents membranes from becoming too rigid at low temperatures or too fluid at high temperatures.

Question 27

What are other functions of cholesterol?

Answer 27

Cholesterol is a precursor for vitamin D, steroid hormones, and bile salts.

Question 28

What are the biological roles of lipids?

Answer 28

Energy storage (high energy density).
Thermal insulation.
Buoyancy for aquatic animals.
Protection (cushioning of organs).
Hormone production (e.g., steroid hormones).

Question 29

How do lipids aid water-repelling functions?

Answer 29

Lipids form hydrophobic barriers, reducing water loss (e.g., in plant leaves and bird feathers).

Question 30

How can you test for the presence of lipids?

Answer 30

Mix the sample with ethanol, then add water. A white emulsion indicates lipids are present.

Question 31

How do phospholipids behave in water?

Answer 31

They form monolayers or bilayers due to their hydrophilic heads and hydrophobic tails.

Question 32

What is the role of phospholipids in surfactants?

Answer 32

Phospholipids act as surfactants by reducing surface tension, aiding interactions between hydrophilic and hydrophobic substances.