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2) Biochemistry II > Lab 2: Lipid Characterization > Flashcards

Lab 2: Lipid Characterization Flashcards

1
Q

What are the three primary functions of fat?

A

1) Storage
2) Cushion to vital organs (ex: kidneys)
3) Insulation

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2
Q

What elements compose fatty acids?

A

Carbon, hydrogen, and oxygen

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3
Q

What group is at the end of a fatty acid chain?

A

Carboxyl

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4
Q

What are triglycerides compose of? How are they joined?

A
  • Glycerol and three fatty acids

- Joined by dehydration synthesis

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5
Q

What is glycerol?

A

A type of alcohol with a hydroxyl group on each of its three carbons

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6
Q

What are lipids soluble in? What are they insoluble in?

A
  • Soluble in solvents (hexane, acetone)

- Insoluble in water

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7
Q

What is saponification? What are the products produced?

A
  • Hydrolysis of a triglyceride with an alkali, such as NaOH

- Sodium salts of the fatty acids and a glycerol

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8
Q

Are fats typically saturated or unsaturated? Why are they solid?

A
  • Saturated (animal sources)

- Straight chains are easier to pack closely together

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9
Q

Do saturated or unsaturated fatty acids have more hydrogens?

A

Saturated fatty acids are SATURATED with hydrogen (more)

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10
Q

Are oils typically saturated or unsaturated? Why are they liquid?

A
  • Unsaturated (plant sources)

- Double bonds induce kinks in the structure, inhibiting close packing

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11
Q

How can we analyze the degree of bond saturation?

A
  • Iodine Value
  • Utilize a halogen solution, such as iodine or bromide
  • Analyze the degree of decolourization of these solutions after it comes into contact with the lipid
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12
Q

What is the basis of the Iodine Value test?

A
  • The more double bonds a fat contains, the more halogen is required
  • A high iodine number means a high degree of unsaturation
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13
Q

How can we analyze differences in chain length?

A

By the differences in intensity of colour due to the absorption of a chemical known as Sudan III

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14
Q

What compound is used to analyze chain length?

A

Sudan III

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15
Q

What compound is used to analyze the degree of bond saturation?

A

Halogen solution (iodine or bromide)

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16
Q

How do water and lipids differ in terms of polarity?

A
  • Water is polar due to differences in electronegativity between O and H
  • Lipids are nonpolar
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17
Q

What happens when a lipid is dissolved in water?

A
  • Water molecules form a cage around lipids, increasing the order and reducing the entropy of the system (thermodynamically unfavourable)
  • Water (polar) and lipids (nonpolar) form two phases in solution
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18
Q

Why is acetone amphiphatic?

A
  • Acetone is hydrophilic due to its polarity

- Acetone may dissolve lipids in water since it can interact with them due to its two methyl side chains

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19
Q

What is needed for saponification?

A

Water since it is a hydrolysis reaction

20
Q

How many molecules of base are needed in saponification? What do they cleave?

A
  • 3 molecules (NaOH or KOH)

- Cleave 3 ester bonds of one TG

21
Q

How does the base break ester bonds in saponification? In between which atoms?

A

OH- nucleophiles of the base break C=O pi bonds in each fatty acid

22
Q

In saponification, how is a carboxylate anion formed?

A
  • Following hydrolysis of the C=O bi bond
  • Intermediate reforms the pi bond, forming an alkoxide leaving group
  • Alkoxide leaving group depronotates the carboxylic acid, resulting in a carboxylate anion
23
Q

What do Na+ cations react with in saponification?

A

React with the anions to form sodium salts of the fatty acids (soaps)

24
Q

What are the products of a saponification reaction of one triglyceride?

A
  • 3 soap molecules

- 1 glycerol

25
Q

What kind of soap molecules does KOH form? Why?

A
  • Liquid soap

- Since it is more water-soluble

26
Q

What kind of soap molecules does NaOH form? Why?

A
  • Solid soap

- Since it is less water-soluble

27
Q

What happens when soap is dissolved in water? What compounds are formed?

A
  • Na+ ions dissolve since charged particles are water-soluble
  • Hydrophilic carboxylate anion is attached to a hydrophobic hydrocarbon chain (amphipathic)
28
Q

How do amphipathic molecules reorient themselves in water?

A

Into micelles, where the anions point outside (thermodynamically favorable)

29
Q

How does the hydrophilic domain of soap interact with hydrophilic compounds?

A

Through hydrogen bonds and ion-dipole interactions

30
Q

How does the hydrophobic domain of soap interact with hydrophobic compounds?

A
  • Trap non-polar compounds in their center

- They are rinsed away with water

31
Q

Why do soap micelles stay dispersed in water?

A

Since the carboxylate anions are charged negatively, which makes them repel one another

32
Q

What is RO-?

A

Alkoxide leaving group

33
Q

What is the role of RO-?

A

Acts as a base by deprotonating the carboxylic acid, resulting in the formation of a carboxylate anion

34
Q

What is the saponification value?

A

The amount of KOH (mg) needed to neutralize the fatty acids from the hydrolysis of 1- gram of oil

35
Q

What do the K+ cations neutralize?

A

The carboxylate anions

36
Q

What is phenolphthalein?

A

Weak acid indicator that is pink in basic solutions, and colourless in acidic solutions

37
Q

What is the role of HCl in the determination of the iodine value?

A

HCl was the titrant, which allowed the determination of the endpoint through the phenolphthalein indicator

38
Q

What does the saponification value indicate?

A

Indicates the average weight of the FAs in a TG

39
Q

Do long-chain fatty acids have lower or higher SV? Why?

A
  • Lower

- Due to fewer carboxylate anions per unit of mass, requiring less KOH for neutralization

40
Q

Is the saponification value of jojoba oil lower or higher than coconut oil?

A

Lower

41
Q

Are lipids soluble in NaOH? Ethanol? Acetone? Chloroform?

A
  • NaOH: no
  • Ethanol: no
  • Acetone: yes
  • Chloroform: yes
42
Q

Does jojoba oil react positively or negatively to the acrolein test? What about coconut oil?

A
  • Jojoba: positive (smelly)

- Coconut: negative (no smell)

43
Q

Did coconut oil produce a hard or soft soap? Why?

A
  • Hard soap
  • Since it mostly contains lauric acid, which is highly saturated –> contributes to the hardness of the soap
  • Saturated fatty acids pack better due to their straight conformation
44
Q

Did jojoba oil produce a hard or soft soap? Why?

A
  • Soft soap
  • Since jojoba oil is a liquid wax
  • Contains little triglycerides, although the ones that it does contain, are all unsaturated
45
Q

What is the reaction in the acrolein test?

A
  • Glycerol reacts with KHSO4

- Produces acrolein (unsaturated aldehyde) and 2 water molecules

46
Q

Did jojoba oil or coconut oil smell from the acrolein test?

A

Coconut oil did, since it contains glycerol

Jojoba oil only contains 3% TG, so very little glycerol (no smell)

2) Biochemistry II (23 decks)

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