Lipids

Question 1

What can lipids be classified into?

Answer 1

1. Simple lipids
2. Compound lipids
3. Lipid derivatives

Question 2

Are lipids macromolecules?

Answer 2

No!
Does not include true polymers, so lipids are unable to form covalent bonds with one another to form other large molecules
Generally not big enough to be considered macromolecules

Question 3

Solubility of lipids?

Answer 3

Insoluble in water as they are non-polar, high solubility in non-polar solvents

Question 4

What is a simple lipid made of?

Answer 4

Only fatty acids and an alcohol (usually glycerol)

Question 5

What are compound lipids made of?

Answer 5

Fatty acids, an alcohol and other groups

Question 6

What is the formula for glycerol?

Answer 6

C3H8O3

Question 7

Is glycerol soluble in water? Why?

Answer 7

Yes! Polar -OH group makes it soluble in water

Question 8

What are fatty acids?

Answer 8

Carboxylic acids composed of an acidic carboxyl (-COOH) functional group at one end and an attached hydrocarbon chain

Question 9

Are fats hydrophobic? Why?

Answer 9

Yes, they are hydrophobic!
Fatty acids possess long carbon skeletons (12-20 carbons) and the abundance of these non-polar C-H bonds make fatty acids hydrophobic

Question 10

How do fatty acids differ?

Answer 10

1. Length of hydrocarbon chain
2. Number and location of double bonds along their carbon skeletons
   Saturated: no double bonds
   Unsaturated: one or more C=C bonds, causing the fatty acid to have a kink in its tail wherever a double bond occurs

Question 11

How does a glyceride form?

Answer 11

The formation of ester linkages between the hydroxyl (-OH) group of glycerol and the carboxyl (-COOH) group of a fatty acid in a condensation reaction where 1 molecule of water is lost

Question 12

How many ester linkages can glycerol form?

Answer 12

　a maximum of 3 as glycerol has 3 -OH groups

Question 13

As the hydrocarbon chain length increases, does the melting point of fats increase or decrease?

Answer 13

Increase!
Longer hydrocarbon chain, more extensive hydrophobic interactions between the chains, higher melting points as more thermal energy is needed to break the bonds

Question 14

What are hydrophobic interactions?

Answer 14

A weak bond that exists between hydrophobic molecules (aka a force of attraction between non-polar molecules)

Question 15

As the degree of unsaturation of the fatty acid tails increase does the melting point of fats increase or decrease?

Answer 15

Decrease!
Unsaturated (has kinks), kinks prevent the molecules from packing closely, hydrophobic interactions are less extensive, less thermal energy is needed to break enough hydrophobic interactions to liquefy the triglycerides

Question 16

Examples of saturated fats? State at rtp?

Answer 16

Most animal fats (butter)
Solid at rtp

Question 17

Examples of unsaturated fats? State at rtp?

Answer 17

Fats of plants and fishes (cooking oil, fish liver oil)
Liquid at rtp
Generally referred to as oils

Question 18

What is another term for fats?

Answer 18

Triglycerides!

Question 19

What is the purpose of triglycerides having a higher proportion of C and H atoms compared to O atoms? Why do triglycerides contain a greater number of carbon atoms per unit mass than carbohydrates?

Answer 19

More efficient energy stores!
Upon oxidation, triglycerides release a larger amount of energy (1g of fat release MORE THAN TWICE as much energy as 1g of carbohydrates) (38 kJ/g vs 17 kJ/g)

Question 20

Why are triglycerides highly reduced molecules? Why do triglycerides have two fold more hydrogen atoms per unit mass than carbohydrates?

Answer 20

Release more water when they are oxidized during cellular respiration compared to carbohydrates
Water is known metabolic water, very important to desert animals (camels)

Question 21

Purpose of triglycerides being hydrophobic?

Answer 21

1. No associated water molecules stored along with triglycerides, no extra weight due to water of hydration
2. Does not affect the water potential of cells when stored in large amounts, keeps animals body mass to a minimum to facilitate locomotion
3. A good thermal insulator as a layer of fat (subcutaneous fat) insulates the body (especially thick in marine animals living in cold climates, known as blubber) (whales, seals)

Question 22

Purpose of hydrocarbon tails being non-polar?

Answer 22

Weak hydrophobic interaction between triglyceride molecules, can slide under pressure
ADIPOSE TISSUE: contains fats, around vital organs to help cushion and protect vital organs against physical impacts

Question 23

Purpose of triglycerides having a lower molecular weight than water per unit volume?

Answer 23

Less dense than water, aids buoyancy for aquatic animals (blubber in whales)

Question 24

Examples of compound lipids?

Answer 24

Phospholipids
Glycolipids

Question 25

What are phospholipids made of?

Answer 25

1 glycerol 2 fatty acids A negatively charged phosphate group Additional small molecules (usually charged or polar) (serine, choline, inositol) can be linked to the phosphate group to for a variety of phospholipids

Question 26

How are phospholipids formed?

Answer 26

2 fatty acids linked to glycerol via ester linkage Phosphate group linked to the third OH group by a phosphodiester linkage

Question 27

Why are phospholipids amphipathic?

Answer 27

2 fatty acid tails that comprise of the hydrocarbon tails are non-polar (hydrophobic) (but can form bond with hydrophobic molecules or among themselves) Phosphate group and its attachments form polar/charged hydrophilic head that has an affinity for water Have both hydrophobic and hydrophilic regions, considered amphipathic

Question 28

What are the 3 types of lipid aggregates?

Answer 28

Micelle Bilateral Liposome/vesicle

Question 29

What is a micelle? What is its function?

Answer 29

Small, spherical droplet consisting of a phospholipid monolayer Phosphate heads on the outside in contact with aqueous environment Hydrocarbon tails restricted to the water-free interior of the micelle Function: transport of fats between gut and body tissues

Question 30

What is a bilayer? Function?

Answer 30

2 lipid monolayers combine Forms a 2 dimensional sheet Hydrophilic heads exposed to the polar exterior Hydrophobic tails in contact with neighboring molecules but excluded from water in the non-polar interior of the bilayer Function: forms selectively permeable cell surface membrane, forms an effective barrier between cell and its external environment

Question 31

What is a liposome/vesicle? Function?

Answer 31

When a lipid bilayer folds back on itself to form a hollow sphere Achieves maximum stability: avoids exposing their hydrophobic edge regions Can enclose aqueous solutions, creating a separate aqueous compartment Function: for storage and transport of cellular products (proteins, lipids etc), digestion of waste (lysosomes), drug delivery in humans

Question 32

What are glycolipids made of?

Answer 32

2 hydrophobic hydrocarbon tails 1 polar, short, carbohydrate chain (less than 15 residues) NO PHOSPHATE

Question 33

How are glycolipids formed?

Answer 33

2 Hydrocarbon tails joined to glycerol backbone via ester linkages Short carbohydrate chain joined to glycerol’s -OH via a glycosidic bond (covalent)

Question 34

Purpose of carbohydrate chain in glyocolipids?

Answer 34

Found at cell surface membrane facing external environment distinguishes one cell from another in cell-cell recognition (cells recognize other cells by binding to these carbohydrate chains) Cell-cell adhesion (binding results in tissue formation)

Question 35

Purpose of hydrophobic interactions between fatty acid tails in glycolipids?

Answer 35

Serve to anchor the entire glycolipids at the cell surface membrane

Question 36

Examples of lipid derivatives?

Answer 36

Steroid hormones, ketone bodies, fatty alcohols, terpenes, carotenoids STEROID CHOLESTEROL