Lipids (2)

Question 1

What is the meaning of the term hydrophobic?
Why is the hydrophobic nature of lipids important?

Answer 1

Hydrophobic means “water-hating.” If the body did not have such molecules, there could be no structure because the water would dissolve everything.

Question 2

Oleic acid has a melting point of 16°C. If you converted the cis double bond into a trans double bond, what would happen to the melting point? Explain.

Answer 2

The melting point would increase. The trans double bonds would fit more in the packing of the long hydrophobic tails, creating more order and therefore more interaction between chains. This would require more energy to disrupt, and hence a higher melting point.

Question 3

Which has the higher melting point: (a) a triglyceride containing only lauric acid and glycerol or (b) a triglyceride containing only stearic acid and glycerol?

Answer 3

(b), because its molecular weight is higher.

Question 4

Predict the order of the melting points of triglycerides containing fatty acids, as follows:

(a) Palmitic, palmitic, stearic
(b) Oleic, stearic, palmitic
(c) Oleic, linoleic, oleic

Answer 4

lowest (c); then (b); highest (a)

Question 5

Rank the following in order of increasing solubility in water (assuming that all are made with the same fatty acids): Explain your answer.
(a) triglycerides
(b) diglycerides
(c) monoglycerides

Answer 5

The more long-chain groups, the lower the solubility;
lowest (a); then (b); highest (c).

Question 6

What are the main types of complex lipids, and what are the main characteristics of their structures?

Answer 6

Complex lipids can be classified into two groups: phospholipids and glycolipids. Phospholipids contain alcohol, two fatty acids, and a phosphate group. There are two types: glycerophospholipids and sphingolipids. In glycerophospholipids, the alcohol is glycerol. In sphingolipids, the alcohol is sphingosine. Glycolipids are complex lipids that contain carbohydrates.

Question 7

How do the unsaturated fatty acids of the complex lipids contribute to the fluidity of a membrane?

Answer 7

The presence of cis double bonds in fatty acids produces greater fluidity because they cannot pack together as closely as saturated fatty acids.

Question 8

What is the difference between an integral and
a peripheral membrane protein?

Answer 8

Integral membrane proteins are embedded in the membrane. Peripheral membrane proteins are found on membrane surfaces.

Question 9

Name all the groups of complex lipids that contain ceramides.

Answer 9

21.25 Complex lipids that contain ceramides include sphingomyelin, sphingolipids, and the cerebroside glycolipids.

Question 10

■ Enumerate the functional groups that contribute to the hydrophilic character of (a) glucocerebroside and (b) sphingomyelin.

Answer 10

The hydrophilic functional groups of (a) glucocerebroside: carbohydrate; hydroxyl and amide groups of the cerebroside. (b) Sphingomyelin: phosphate group; choline; hydroxyl and amide of ceramide.

Question 11

Where can pure cholesterol crystals be found in the body?

Answer 11

Cholesterol crystals may be found in (1) gallstones, which are sometimes pure cholesterol, and (2) joints of people suffering from bursitis.

Question 12

How does LDL deliver its cholesterol to the cells?

Answer 12

LDL from the bloodstream enters the cells by binding to LDL receptor proteins on the surface. After binding, the LDL is transported inside the cells, where cholesterol is released by enzymatic degradation of the LDL.

Question 13

How does VLDL become LDL?

Answer 13

Removing lipids from the triglyceride cores of VLDL particles increases the density of the particles and converts them from VLDL to LDL particles.

Question 14

How does the serum cholesterol level control both cholesterol synthesis in the liver and LDL uptake?

Answer 14

When serum cholesterol concentration is high, the synthesis of cholesterol in the liver is inhibited and the synthesis of LDL receptors in the cell is increased. Serum cholesterol levels control the formation of cholesterol in the
liver by regulating enzymes that synthesize cholesterol.

Answer 15

Estradiol (E) is synthesized from progesterone (P) through the intermediate testosterone (T). First, the D-ring acetyl group of P is converted to a hydroxyl group and T is produced. The methyl group in T, at the junction of rings A and B, is removed, and ring A becomes aromatic. The keto group in P and T is converted to a hydroxyl group in E.

Question 16

What are Lipids?

Answer 16

• found in living organisms
• insoluble in water
• soluble in nonpolar or low-polar solvents

Question 17

• found in living organisms
• insoluble in water
• soluble in nonpolar or low-polar solvents

Answer 17

Lipids

Question 18

3 major roles of lipids in human biochemistry

Answer 18

• store energy within the fat cells
• part of the membrane that separates compartments of aqueous solution from each other
• serves as chemical messenger

Question 19

Classification of Lipids

Answer 19

• Simple lipids
• Compound lipids
• Terpenes and Steroids

Question 20

are physiologically potent regulatory
molecules such as prostaglandins,
thromboxanes and leukotrienes

Answer 20

Eicosanoids

Question 21

– solid at room temperature
– obtained from animal sources
– contain a greater proportion of saturated fatty acids

Answer 21

fats

Question 22

• liquid at room temperature
• of plant origin
• contain a greater percentage of unsaturated fatty acids

Answer 22

oils

Question 23

are esters composed of three fatty acids joined to the trihydroxy alcohol, glycerol.

Answer 23

Triglycerides or triacylglycerols (TAG)

Question 24

• are long-chain monocarboxylic acids
• contains even number of carbon atoms (the consequence of their biosynthesis)
• most common: 12–18 C

Answer 24

Fatty Acids

Question 25

melting points of saturated fatty acids decrease with decreasing carbon number.

Answer 25

TRUE. melting points of saturated fatty acids increase with increasing carbon number.

Question 26

saturated fatty acids containing ten or more carbons are LIQUID at room temperature.

Answer 26

FALSE. saturated fatty acids containing ten or more carbons are SOLID at room temperature.

Question 27

melting point of a saturated fatty acid is greater than that of an unsaturated fatty acid of the same chain length.

Answer 27

TRUE. melting point of a saturated fatty acid is greater than that of an unsaturated fatty acid of the same chain length.

Question 28

- a precursor for the synthesis of prostacyclin * inhibits the clumping of platelets * reduces clot formation.

Answer 28

EPA

Question 29

* one of the major fatty acids in the phospholipids of sperm and brain cells and retina * reduce triglyceride levels (although the mechanism is not understood).

Answer 29

DHA

Question 30

* reduce the incidence of cardiovascular disease * not clear whether it acts alone or because it is the precursor of DHA and EPA.

Answer 30

ALA

Question 31

essential fatty acid, required for the synthesis of arachidonic acid, the precursor for many prostaglandins.

Answer 31

Linoleic acid

Question 32

* precursors of prostaglandins * anti-inflammatory effects

Answer 32

Omega-3 fatty acids

Question 33

* precursors to prostaglandins * inflammatory effects.

Answer 33

Omega-6 fatty acids

Question 34

* colorless, tasteless, and odorless * characteristic colors, odors, and flavors associated with lipids are imparted to them by foreign substances that have been absorbed by the lipid and are soluble in them.

Answer 34

Pure fats & Oils

Question 35

– addition of H2 to double bonds of unsaturated fatty acids in lipids, converting them to single bonds of saturated fatty acids.

Answer 35

Hydrogenation

Question 36

best way to convert unsaturated liquid oils to solids

Answer 36

Hydrogenation

Question 37

Complete hydrogenation gives a very SOFT product

Answer 37

FALSE. BRITTLE

Question 38

partial hydrogenation of a liquid vegetable oil changes it to a SOFT, semisolid fat.

Answer 38

TRUE

Question 39

addition of water to ester bonds of lipids in the presence of strong acids or digestive enzymes called lipases.

Answer 39

Hydrolysis

Question 40

the reaction of lipids with a strong base (alkaline hydrolysis) to give glycerol and salts of the fatty acids

Answer 40

Saponification

Question 41

sulfates of fatty acids or sulfonate salts of hydrocarbons

Answer 41

Anionic detergents

Question 42

referred to as inverted soap because their water-soluble end carries a positive, rather than negative charge; widely used in hospitals, good cleansing agents, have germicidal properties

Answer 42

Cationic detergents

Question 43

contain polar covalent structures that provide the required water solubility; used extensively in dishwashing liquid and on all occasions that call for the absence of inorganic ions.

Answer 43

Nonionic detergents

Question 44

* a fat or oil becomes rancid when its double bonds are oxidized by oxygen and microorganisms. * the oxidation products are short – chain fatty acids and aldehydes that have very disagreeable odors.

Answer 44

Oxidation

Question 45

fat and oil develop a disagreeable odor caused by hydrolysis and oxidation.

Answer 45

Rancidity

Question 46

Under moist and warm conditions, ______ of the ester linkages occurs, liberating the volatile acids. Microorganisms present in the air furnish the enzyme (lipases) that catalyze the process. Rancidity can easily be prevented by storing butter covered in a refrigerator.

Answer 46

Hydrolytic rancidity

Question 47

Rancidity occurs in triglycerides containing unsaturated fatty acids.

Answer 47

Oxidative rancidity

Question 48

are compounds added to foods in very small amounts (0.01–0.001%) to suppress rancidity.

Answer 48

Antioxidants

Question 49

is an ester of a saturated fatty acid and a long-chain alcohol, each containing from 14 to 30 carbon atoms.

Answer 49

wax

Question 50

found in the surfaces of leaves and stems and serve to protect the plant from dehydration and from invasion by harmful organisms.

Answer 50

Plant waxes

Question 51

also serve as protective coatings; found on the the surface of feathers, skin, and hair and help keep these surfaces soft and pliable

Answer 51

Animal waxes

Question 52

similar to soap and detergents because of hydrophobic tails and hydrophilic heads but differs in having two tails instead of one.

Answer 52

membrane lipids

Question 53

are the primary components in the cellular membrane (lipid bilayer)

Answer 53

Phospholipids

Question 54

substances that can coat droplets of nonpolar liquids and hold them in water. suspension in water.

Answer 54

Emulsifying agents

Question 55

contains the important quaternary ammonium salt, choline, joined to the phosphoric acid residue.

Answer 55

Lecithin

Question 56

ethanolamine or serine, is linked to the phosphate moiety

Answer 56

Cephalins

Question 57

characterized by the presence of a single monosaccharide head group;

Answer 57

Cerebrosides

Question 58

the coating of nerve axons, conataining a different kind of complex lipid

Answer 58

Myelin

Question 59

- most important lipids in the myelin sheaths of nerve cells - associated with diseases such as multiple sclerosis

Answer 59

Sphingomyelins

Question 60

found in the membranes of macrophages (cells that protect the body by ingesting and destroying foreign microorganisms)

Answer 60

glucocerebroside

Question 61

found almost exclusively in the membranes of brain cells

Answer 61

galactocerebroside

Question 62

- possess oligosaccharide groups, including one or more molecules of N -acetylneuraminic acid (sialic acid) - found in most tissues in the body.

Answer 62

Gangliosides

Question 63

The important feature of biological membranes

Answer 63

1. Membrane fluidity 2. Selective permeability 3. Self-sealing capability 4. Asymmetry

Question 64

Transport wherein there is no direct energy input.

Answer 64

Passive transport

Question 65

– molecules move through a membrane down a concentration gradient (towards lower concentration)

Answer 65

simple diffusion

Question 66

molecules move through protein channels in membrane; permease, - a membrane protein assists in diffusion.

Answer 66

facilitated diffusion

Question 67

Transport that requires energy.

Answer 67

Active transport

Question 68

– energy is provided by ATP (e.g., Na+ - K+ pump system)

Answer 68

primary

Question 69

concentration gradients generated by the primary active transport are used to move substances across membranes (e.g., Na+ gradient from Na+- K+the pump system is used to transport glucose in kidney tubules).

Answer 69

secondary

Question 70

- The most common and important complex lipids - which are responsible for the transport of other lipids in the body.

Answer 70

plasma lipoproteins

Question 71

4 major classes of human plasma lipoproteins

Answer 71

- Chylomicrons - Very low density lipoproteins (VLDL) - Low-density lipoproteins (LDL) - High-density lipoproteins (HDL)

Question 72

– carry dietary triglycerides from the intestine to other tissues.

Answer 72

Chylomicrons

Question 73

– bind triglycerides synthesized in the liver and carry them to adipose and other tissues for storage.

Answer 73

Very low density lipoproteins (VLDL)

Question 74

– carries cholesterol to peripheral tissues and help regulate cholesterol levels in those tissues; richest in cholesterol, frequently carrying 40% of the plasma cholesterol; allows accumulation.

Answer 74

Low-density lipoproteins (LDL)

Question 75

– bound to plasma cholesterol; however, they transport cholesterol from peripheral tissues to the liver for removal.

Answer 75

High-density lipoproteins (HDL)

Question 76

2 Important function of cholesterol

Answer 76

1. Regulator of membrane fluidity 2. Cholesterol serves as the body’s starting material for the synthesis of all other steroids (e.g. steroid hormones and bile salts).

Question 77

2 major classes of steroid hormone

Answer 77

1. Sex hormones 2. Adrenocortical hormones

Question 78

Sex hormones essential for preparing the uterus for implantation of a fertilized ovum during pregnancy.

Answer 78

progestin e.g. progesterone

Question 79

regulate a variety of metabolic processes

Answer 79

Adrenocortical hormones

Question 80

Aldosterone controls tissue swelling by regulating the delicate cellular salt balance between Na+ and K

Answer 80

mineralocorticoids

Question 81

Involved in the regulation of glucose metabolism and in the control of inflammation (e.g. used in the treatment of rheumatoid arthritis, asthma, GI disorder, many skin conditions and a variety of other diseases).

Answer 81

glucocorticoids e.g. hydrocortisone and cortisone

Question 82

- oral contraceptives and anabolic agents.

Answer 82

Synthetic Steroids

Question 83

produced by the liver (from cholesterol), stored in the gall bladder and secreted into the intestine.

Answer 83

Bile Salts

Question 84

play a major role in the regulation of calcium and phosphorus metabolism.

Answer 84

Vitamin D

Question 85

ergocalciferol (vegetable origin)

Answer 85

Vitamin D2

Question 86

cholecalciferol (animal origin);

Answer 86

Vitamin D3

Question 87

One of the most important of these compounds vitamins is formed from cholesterol by the action of ultraviolet radiation from the sun.

Answer 87

vitamin D

Question 88

These lipids are found in the oils of some plants and flowers that give them their characteristic odors and colors.

Answer 88

Terpenes

Question 89

Terpenes are composed of two or more sections containing five-carbon conjugated structure called _______.

Answer 89

isoprene

Question 90

Vitamins required for the formation of the visual a pigment found in the retina of the eye.

Answer 90

Vitamin A

Question 91

- Vitamins found in the plant world in the form of carotenes.

Answer 91

Provitamin A

Question 92

(α-tocopherol) prevents oxidation of unsaturated fatty acids in cellular membranes (antioxidant).

Answer 92

Vitamin E

Question 93

- antihemorrhagic vitamin – needed in the formation of prothrombin for blood clotting (phylloquinone) - synthesized by intestinal bacteria.

Answer 93

Vitamin K

Question 94

- are hormone-like molecules. - not transported in the bloodstream to their site of action but exert their effects in the tissues where they are synthesized. - The name ______is derived from the Greek word ____, meaning twenty, because they are all derivatives of 20 carbon fatty acids, arachidonic acid.

Answer 94

Eicosanoids:eikos

Question 95

is the precursor for the different prostaglandins, leukotrienes and thromboxanes.

Answer 95

Arachidonic acid

Question 96

unsaturated carboxylic acids consisting of a 20–carbon skeleton that contains a cyclopentane ring; extremely potent biological molecules with hormone-like activity.

Answer 96

Prostaglandins

Question 97

– contain three conjugated double bonds and differ from prostaglandins by the absence of the ring.

Answer 97

Leukotrienes

Question 98

– differ from the other eicosanoids in that their structures have a cyclic ether; thromboxane A2 - the most prominent member of this group, is primarily produced by platelets; ____ -promotes platelet aggregation and smooth muscle contraction.

Answer 98

Thromboxanes