Biology 1113: Lecture 6 (lipids)

Question 1

What is the primary unifying characteristic of lipids?

Answer 1

They do not dissolve easily in water (hydrophobic due to nonpolar C-H chains/rings).

Question 2

What are the three main categories of lipids?

Answer 2

Triglycerides (fats): Energy storage.
Phospholipids: Cell membranes.
Steroids: Hormones and cell membrane components.

Question 3

Do lipids have true monomers?

Answer 3

No, they are defined by their hydrophobicity rather than specific monomers.

Question 4

What is a triglyceride made of?

Answer 4

Glycerol + 3 fatty acids.

Question 5

How do fatty acids differ?

Answer 5

Length (number of carbons).
Number of double bonds (saturation).

Question 6

What is the difference between saturated and unsaturated fatty acids?

Answer 6

Saturated: No double bonds, straight chains, solid at room temperature.
Unsaturated: At least one double bond, kinked chains, liquid at room temperature.

Question 7

What are trans fats, and why are they harmful?

Answer 7

Fats with trans double bonds created artificially (e.g., hydrogenation).
They are solid at room temperature, hard to digest, and linked to health issues like heart disease.

Question 8

Why do triglycerides store more energy than carbohydrates?

Answer 8

They contain more C-H bonds, which store more energy.

Question 9

What is the structure of a phospholipid?

Answer 9

Glycerol + 2 fatty acids + a phosphate group with a polar head.

Question 10

What does ‘amphipathic’ mean?

Answer 10

Molecules with both hydrophobic (nonpolar) and hydrophilic (polar) regions.

Question 11

Why are phospholipids important in cell membranes?

Answer 11

They form bilayers, with hydrophobic tails inward and hydrophilic heads outward, creating a selective barrier.

Question 12

What is the structure of steroids?

Answer 12

Four fused rings of carbon and hydrogen.

Question 13

What is the most common steroid, and what are its functions?

Answer 13

Cholesterol:
Component of cell membranes.
Precursor for steroid hormones (e.g., testosterone, estrogen).

Question 14

What are essential fatty acids?

Answer 14

Fatty acids humans cannot produce (e.g., omega-3 and omega-6) and must obtain through diet.

Question 15

Why are essential fatty acids important?

Answer 15

They are necessary for phospholipid synthesis, brain function, and heart health.

Question 16

Why do organisms store energy in both lipids and carbohydrates?

Answer 16

Lipids: Long-term, high-energy storage (9 calories/gram).
Carbohydrates: Short-term, quick energy source (4 calories/gram).

Question 17

Why is glycogen preferred for short-term energy storage?

Answer 17

It is water-soluble and stored in the liver and muscles for quick access.

Question 18

What determines membrane permeability?

Answer 18

Saturation of fatty acids (unsaturated increases fluidity).
Temperature (higher temperature increases permeability).

Question 19

What types of molecules easily pass through a lipid bilayer?

Answer 19

Small, nonpolar molecules (e.g., gases like O2).

Question 20

What types of molecules cannot pass through without assistance?

Answer 20

Large or charged molecules (e.g., ions).

Question 21

How do phospholipids form membranes?

Answer 21

Their amphipathic nature causes them to spontaneously form bilayers or micelles in water.

Question 22

Why are lipids defined by their physical properties?

Answer 22

They are characterized by hydrophobicity rather than specific monomers.

Question 23

Why are most phospholipids unsaturated?

Answer 23

The kinks from double bonds increase membrane fluidity and permeability.

Question 24

What is the role of temperature in membrane fluidity?

Answer 24

Higher temperatures increase fluidity, while lower temperatures decrease it.

Question 25

What are the risks associated with trans fats?

Answer 25

Increased risk of heart disease, diabetes, and obesity.
Difficult for enzymes to digest properly.

Question 26

What are omega-3 and omega-6 fatty acids, and where are they found?

Answer 26

Types of essential unsaturated fatty acids.
Found in fish, nuts, and seeds.