lec 5

Question 1

What are lipids?

Answer 1

Non-polar organic compounds, including fats, oils, waxes, sterols, and fat-soluble vitamins (A, D, E, and K).

Question 2

What forms do lipids exist in?

Answer 2

Liquids (oils) or solids (fats).

Question 3

What are the types of glycerides based on fatty acid esters?

Answer 3

Monoglycerides, diglycerides, and triglycerides.

Question 4

What are fatty acids?

Answer 4

Straight-chain aliphatic carboxylic acids that vary in length, saturation, and type of saturation.

Question 5

What are the three main types of fatty acids?

Answer 5

Saturated fats, cis unsaturated fats, and trans unsaturated fats.

Question 6

What does “cis” mean in fatty acids?

Answer 6

“on the same side,” naturally occurring.

Question 7

What does “trans” mean in fatty acids?

Answer 7

“across,” typically industrially produced but also found naturally in dairy.

Question 8

hat is the difference between even and random fatty acid distribution?

Answer 8

Even distribution: Fatty acids are as evenly spread as possible across triglycerides.
Random distribution: Fatty acids are randomly placed with no preferences.

Question 9

What is restricted random fatty acid distribution?

Answer 9

Fatty acids are randomly distributed, but some positions on the triglyceride are preferred.

Question 10

What are semi-crystalline solids?

Answer 10

Solids with ordered polycrystalline structures but also contain amorphous oil phases.

Question 11

What are the two stages of crystallization in fats?

Answer 11

Nucleation (formation of initial crystals) and crystal growth (enlargement of nuclei).

Question 12

What is supersaturation in lipids?

Answer 12

The temperature difference between melting and crystallization, driven by undercooling.

Question 13

What are the two types of nucleation in lipids

Answer 13

Homogeneous (large undercooling, nuclei form at once) and heterogeneous (low undercooling, nuclei form around other nuclei).

Question 14

How does nucleation and growth rate affect crystal size?

Answer 14

High nucleation rate = More, smaller crystals.
High growth rate = Fewer, larger crystals.

Question 15

What is polymorphism in lipids?

Answer 15

The ability of identical TAGs to have different crystal packing, affecting fat properties.

Question 16

What happens during polymorphic transformations?

Answer 16

They move towards more stable forms, with higher melting points.

Question 17

What are the crystal sizes of different polymorphs?

Answer 17

α and β’ = Small crystals (< 5 μm).
β = Large crystals (~50 μm), often gritty.

Question 18

What is the tempering process for chocolate?

Answer 18

Melt TAGs → Cool to form β-V nuclei → Heat to melt β’ but not β-V → Allow β-V nuclei to grow.

Question 19

What is hydrolytic rancidity in lipids?

Answer 19

Lipid breakdown by water or enzymes, causing smells, foaming, and smoke.

Question 20

What is lipid oxidation?

Answer 20

Oxygen reacts with unsaturated lipids, leading to spoilage and reduced shelf life.

Question 21

How does the number of double bonds affect oxidation?

Answer 21

More double bonds = Faster oxidation rate.

Question 22

What are common initiators of lipid oxidation?

Answer 22

Metals (Fe, Cu, Mn), heat, light, and radicals.

Question 23

What happens during the initiation stage of lipid oxidation?

Answer 23

A hydrogen atom is removed, forming a fatty acid radical stabilized by resonance.

Question 24

What is the propagation stage in lipid oxidation?

Answer 24

Free radicals transfer, forming unstable lipid hydroperoxides (LOOH).

Question 25

What happens during hydroperoxide breakdown?

Answer 25

Hydroperoxides decompose into alkoxy and hydroxyl radicals, which are highly reactive.

Question 26

What is termination in lipid oxidation?

Answer 26

Free radicals stabilize by recombining or reacting with water, slowing oxidation and causing rancidity.

Question 27

What happens during lipid oxidation termination

Answer 27

Free radicals break down into small compounds like ketones and aldehydes, causing off flavors, odors, and increased oil viscosity.

Question 28

What are the two classes of antioxidants?

Answer 28

Primary antioxidants: React with radicals to stop chain reactions. Secondary antioxidants: Deactivate pro-oxidants and quench UV light.

Question 29

What are the requirements for primary antioxidants?

Answer 29

They must donate hydrogen, stabilize free radicals, have conjugation, and provide steric hindrance.

Question 30

How do primary antioxidants work?

Answer 30

They donate hydrogen, stabilize unpaired electrons via resonance, and terminate radicals through reactions.

Question 31

What is hydrogenation in lipids?

Answer 31

A process that stabilizes oils by removing double bonds, converting unsaturated fats to saturated or trans fats.

Question 32

What are the steps in hydrogenation?

Answer 32

1.Double bond interacts with the metal catalyst. 2.Hydrogen adsorbs to the catalyst surface. 3.Hydrogen attaches to one carbon of the double bond. 4.Another hydrogen attaches, releasing the fatty acid.

Question 33

What is partial hydrogenation?

Answer 33

A process that causes cis-trans and positional isomerization of double bonds, now banned in Canada.

Question 34

What is full hydrogenation?

Answer 34

It completely saturates the fat, leaving no double bonds and is used for stability in products like frying oils.

Question 35

What is interesterification in lipids?

Answer 35

A process that randomizes the position of fatty acids in triglycerides.

Question 36

How do fatty acids affect cardiovascular health?

Answer 36

Oxidized LDLs and foam cells form plaques in arteries, leading to atherosclerosis and hardened vessels.

Question 37

What are plaques made of in atherosclerosis?

Answer 37

Foam cells (oxidized LDL + macrophages) and calcium, forming hard and insoluble deposits.

Question 38

What are aliphatic side chains in amino acids?

Answer 38

AVLIGP (Alanine, Valine, Leucine, Isoleucine, Glycine, Proline).

Question 39

What are polar neutral side chains in amino acids?

Answer 39

STNQ (Serine, Threonine, Asparagine, Glutamine).

Question 40

What are sulfur-containing side chains in amino acids?

Answer 40

CM (Cysteine, Methionine).

Question 41

What are aromatic side chains in amino acids?

Answer 41

FWY (Phenylalanine, Tryptophan, Tyrosine).

Question 42

What are cationic side chains in amino acids?

Answer 42

HKR (Histidine, Lysine, Arginine).

Question 43

What are anionic side chains in amino acids?

Answer 43

DE (Aspartic acid, Glutamic acid).

Question 44

How are amino acids linked in proteins?

Answer 44

By peptide bonds formed via a dehydration reaction, making the bond rigid and planar.

Question 45

What is the primary structure of a protein?

Answer 45

The sequence of amino acids modified only by hydrolysis or chemical modifications like phosphorylation or glycosylation.

Question 46

What is the secondary structure of a protein?

Answer 46

Local conformations like β-sheets and α-helices formed by the polypeptide backbone.

Question 47

What stabilizes protein tertiary structure?

Answer 47

Covalent (disulfide bridges) and non-covalent (salt bridges, hydrogen bonds, van der Waals forces) interactions.

Question 48

What is the quaternary structure of a protein?

Answer 48

A structure formed by more than one polypeptide chain, e.g., myoglobin.

Question 49

What is the difference between parallel and antiparallel β-sheets?

Answer 49

Parallel sheets have angled H-bonds, while antiparallel sheets have straight H-bonds.

Question 50

What is protein denaturation?

Answer 50

The unfolding of secondary, tertiary, and quaternary structures due to environmental changes.

Question 51

What agents cause protein denaturation?

Answer 51

Heat, pH changes, ionic strength, solvent polarity, and shear.

Question 52

What are the effects of protein denaturation?

Answer 52

Decreased solubility, increased digestibility, reduced activity, increased viscosity, and higher water-binding.

Question 53

How does collagen form gelatin and jello?

Answer 53

Heat denatures collagen, and cooling allows partial refolding, creating a gel network.

Question 54

What is intraesterification?

Answer 54

Rearranges fatty acids within the same triglyceride molecule, changing their positions on the glycerol backbone without altering chemical composition.

Question 55

How does intraesterification differ from interesterification?

Answer 55

Intraesterification occurs within one molecule, while interesterification involves fatty acid exchange between different triglycerides.