Ch 5 - Lipid Structure and Function

Question 1

Where are lipids soluble and insoluble?

Answer 1

• soluble in water

- insoluble in nonpolar organic solvents

Question 2

What are phospholipids and what do they form?

Answer 2

• amphipathic and form the bilayer of biological membranes

- contain hydrophilic (polar) head group and hydrophobic (nonpolar) tails

Question 3

What attaches the head of the phospholipid and what does it determine?

Answer 3

• attached by a phosphodiester linkage

- because it interacts with the environment, determines the function of the phospholipid

Question 4

What does the saturation of the fatty acids determine?

Answer 4

the fluidity of the membrane; saturated fatty acids are less fluid than unsaturated ones
- fatty acids form most of the structural thickness of the phospholipid bilayer

Question 5

What are glycerophospholipids?

Answer 5

phospholipids that contain a glycerol backbone

Question 6

What do sphingolipids contain?

Answer 6

a sphingosine and sphingoid backbone

Question 7

What are sphingophospholipids?

Answer 7

the many (but not all) sphingolipids that are phospholipids and contain a phosphodiester bond

Question 8

What are sphingomyelins?

Answer 8

• the major class of sphingophospholipids and contain a phosphatidylcholine or phosphatidylethanolamine head group
• they are a major component on the myelin sheath

Question 9

What are glycosphingolipids attached to?

Answer 9

sugar moieties instead of phosphate groups

Question 10

What is the difference between cerebrosides and globosides?

Answer 10

• cere: have one sugar connected to the sphingosine

- glob: have 2+

Question 11

What do gangliosides contain?

Answer 11

oligosaccharides with at least on terminal N-acetylneuraminic acid (NANA; also called sialic acid)

Question 12

What do waxes contain and what are they used for?

Answer 12

• long-chain fatty acids esterified to long-chain alcohols

- used as protection against evaporation and parasites in plants and animals

Question 13

What are terpenes?

Answer 13

odiferous steroid precursors made from isopren, a 5-carbon molecule
- 1 terpene unit (a monoterpene) contains 2 isoprene units

Question 14

What are terpenoids derived from?

Answer 14

from terpenes via oxygenation or backbone rearrangement

- have similar odorous characteristic

Question 15

What do steroids contain and how they to differ?

Answer 15

• contain 3 cyclohexane rings and on cyclopentane ring

- their oxidation state and functional groups may vary

Question 16

What is the difference between steroid hormones and cholesterol?

Answer 16

• steroid: have affinity receptors, work at low concentrations, and affect gene expression and metabolism
• cholesterol: important to membrane fluidity and stability; it serves as a precursor to a host of other molecules

Question 17

What are prostaglandins and what do they affect?

Answer 17

• autocrine and paracrine signaling molecules that regulate cAMP levels
• have powerful effects on smooth muscle contraction, body temperature, sleep-wake cycle, fever, and pain

Question 18

What are the fat soluble viatmine?

Answer 18

A, D, E, and K

Question 19

What is Vitamin A (carotene) metabolized for?

Answer 19

to retinal for vision and retinoic acid for gene expression in epithelial development

Question 20

What is Vitamin D (cholecalciferol) metabolized for?

Answer 20

to calcitriol in the kidneys and regulates calcium and phosphorus homeostasis in the intestines (increasing calcium and phosphate absorption), promoting bone formation
- a deficiency causes rickets

Question 21

What is Vitamin E (tocopherols) act as?

Answer 21

biological antioxidants

- their aromatic rings destroy free radicals, preventing oxidative damage

Question 22

What is Vitamin K (phylloquinone and menaquinones) used for?

Answer 22

• important for formation of prothrombin, a clotting factor

- performs posttranslational modifications on a number of proteins, creating calcium-binding sites

Question 23

What are triaclyglycerols (triglycerides)? What do they contain?

Answer 23

• the preferred method of storing energy for long term use
• contain one glycerol attached to 3 FA by ester bonds (the FA usually vary within the same triglyceride)
• very hydrophobic, so they are not hydrated by body water and do not carry additional water weight

Question 24

What does the carbon atoms in lipids being more reduced than carbohydrates affect during oxidation?

Answer 24

gives twice as much energy per gram during oxidation

Question 25

What are adipocyte?

Answer 25

animal cells specifically used for storage of large triacylglycerol deposits

Question 26

What are free fatty acids and what are their salts?

Answer 26

• unesterified FA that travel in the blood stream

- salts of free FA are soaps and can be synthesized in saponification

Question 27

What is saponification?

Answer 27

the ester hydrolysis of triacylglycerols using a strong base, like sodium or potassium hydroxide

Question 28

What is micelle?

Answer 28

• soaps acts as surfactants, forming micelle
• they can dissolve a lipid-soluble molecule in its FA core, and wash away with water because of its shell of carboxylate head groups

Question 29

Which components of membrane lipids contribute to their structural role in membranes? Which components contribute to function?

Answer 29

• membrane lipids are amphipathic: they have hydrophilic heads and hydrophobic tails, allowing for the formation of bilayers in aqueous solution
• the FA tails form the bulk of the phospholipid bilayer, and play predominantly structural role
• the functional differences between membrane lipids are determined by the polar head group, due to its constant exposure to the exterior environment of the phospholipid bilayer
• the degree of unsaturation of FA tails can also play a small role in function

Question 30

What is the difference between a sphingolipid that is also a phospholipid and one that is not?

Answer 30

• the difference is the bond between sphingosine backbone and the head group
• when this a phosphodiester bond, it’s a phospholipid
• non phospholipid sphingolipids include glycolipids, which contain glycosidic linkage to a sugar

Question 31

What are the 3 types of sphingolipids and their characteristics of phospho/glycolipid and functional groups?

Answer 31

• sphingomyelin (phospholipid): phosphatidylethanolamine/phosphatidylcholine
• glycosphingolipid (glycolipid): sugars (mono/polysaccharide)
• ganglioside (glycolipid): oligosaccharides and N-acetylneuraminic acid (NANA)

Question 32

What would happen in an amphipathic molecule were placed in a nonpolar solvent rather than an aqueous solution?

Answer 32

• in a nonpolar solvent, we would see the opposite of what happens in a polar solvent like water: the hydrophilic, polar part of the molecules would be sequestered inside, while the nonpolar, hydrophobic part of the molecules would be found on the exterior and exposed to the solvent

Question 33

How many carbons are in a diterpene?

Answer 33

20 carbon molecules in its backbone

- 1 terpene unit is made of 2 isoprene units, each of which has 5 carbons

Question 34

What is the difference between a steroid and a steroid hormone?

Answer 34

• steroid: defined by its structure: includes cyclohexane rings and a cyclopentane ring
• steroid hormone: molecule within its class that also functions as a hormone, meaning that it travels in the bloodstream, is active at low concentrations, has high affinity receptors, and affects gene expression and metabolism

Question 35

How does the human body store spare energy? Why doesn’t the human body store most energy as sugar?

Answer 35

• human body stores energy as glycogen and triaclyglycerols
• tri are preferred because their carbons are more reduced, resulting in a larger amount of energy yield per unit weight
• due to their hydrophobic nature, tri do not need to carry extra weight from hydration

Question 36

What bonds are broken during saponification?

Answer 36

ester bonds of triacylglycerols are broken to form glycerol molecule and the salts of fatty acids (soaps)