Lipids 1

Question 1

Lipids

4 points

Answer 1

1. member of a broad group of compounds that include fats, oils, waxes, steroids and various resins
2. Many different chemical and physical structures
3. Insoluble in water and polar solvents
4. Soluble in non-polar (organic) solvents such as chloroform

Question 2

Functions of lipids

Storage

Answer 2

1. Store of energy in fats and oils eg. adipose tissue in animals, oils in oil seeds (eg. sunflower)

Question 3

Function of lipids

Structural

Answer 3

Protection - waxes on leaves, lanolin on wool giving waterproofing and protection; adipose tissue around organs

eg. perirenal adipose tissue around kidney

Question 4

Function of lipids - Structural

Insulation

Answer 4

subcutaneous adipose tissue acts as insulation barrier under skin

Question 5

Function of lipids - Structural

Membranes

Answer 5

provide non-polar barrier around cells and cell organelles separating essentially aqueous environments

Question 6

Function of lipids

Metabolic

Answer 6

1. Metabolic control via steroid hormones and eicosanoids

2. Fat soluble vitamins (A, D, E, K)

Question 7

Function of lipids

Industrial uses

Answer 7

1. Manufacture of food oils, margarines and shortenings; oil-seed cakes for animal feeds; industrial oils and biodiesel; soaps, varnishes and paints; cosmetics and pharmaceuticals

Question 8

3 types of lipid

Answer 8

Fatty Acids – building blocks

Triacylglycerols – energy stores (triglycerides)

Phosphoacylglycerols – membranes (phospholipids)

Question 9

Fatty Acids (FAs)
5 points

Answer 9

1. Composed of a hydrocarbon “tail” and a carboxyl group (-COOH) “head”.
2. The hydrocarbon tail is made up only of hydrogen and carbon and is non-polar.
3. The carboxyl group has two polar groups - the C=O and O-H
4. Short hydrocarbon tail – molecule has some polar properties
5. Long hydrocarbon tail – molecule has very little polar character

Question 10

Short Chain Fatty Acids

6 points

Answer 10

1. AKA Volatile Fatty Acids (VFAs)
2. Contain 2-5 C atoms in the molecule
3. Are volatile and have characteristic pungent odours.
4. Often produced by micro-organisms during fermentation: in cheese, silage, vinegar, rumen and large bowel.
5. They are miscible with water
6. Are weak acids

Question 11

Short Chain Fatty Acids

Name and trivial name (4)

Answer 11

1. 2 C
   Ethanoic acid
   Acetic acid
   CH3COOH
2. 3C
   Propionic acid
   Propionic acid
   CH3CH2COOH
3. 4 C
   Butanoic acid
   Butryic acid
   CH3(CH2)2COOH
4. 5C
   Pentanoic acid
   Valeric acid
   CH3(CH2)3COOH

Question 12

Long Chain Fatty Acids (LCFAs)

6 points

Answer 12

1. Contain >5 C atoms
2. Naturally occurring LCFAs have even numbers of C atoms
3. Very important as part of more complex lipid molecules
4. 2 types – saturated and unsaturated
5. Saturated have no C=C double bonds
6. Unsaturated have 1 or more C=C double bond

Question 13

Saturated Fatty Acids

3 points

Answer 13

1. the general formula CH3(CH2)nCOOH
2. Many molecules of the same type of fatty acid can pack closely together and interact.
3. The longer the hydrocarbon tail the more interactions - an increase in melting point with increase in chain length

Question 14

names and carbon number of 2 saturated fatty acids

Answer 14

1. 16
   Hexadecanoic acid
   Palmitic acid [trivial]
2. 18
   Octadecanic acid
   Stearic acid

Question 15

Unsaturated fatty acids (SFAs)

Answer 15

1. Contain 1 or more carbon-carbon double bond in the hydrocarbon chain
2. cis is the normal configuration. [same side, trans opposite side]
3. cis configuration puts a kink into the molecule
4. Makes it difficult for molecules to pack together

Question 16

Fatty acids shorthand

way to number carbon atoms and double bonds

Answer 16

1. From the carboxylic acid OR
   From the methyl group (omega w system)
2. The number of double bonds is indicated by a number following a colon ( : )
   An 18:3 fatty acid has 18 carbon atoms and three double bonds

Question 17

Fatty acids shorthand The position of double bonds is indicated either by
2 points

Answer 17

1. The Triangle sign followed by the number of the carbon atom(s) at which the double bond(s) start, eg triangle 6,9,12,15
2. Stating that it is a n3 or n6 (w3 or w6) fatty acid - the first double bond starts on the C atom third (n3) or sixth (n6) from the methyl (CH3) end of the fatty acid

Question 18

Unsaturated Fatty acids (SFAs)

C, Triangle, Name, Trivial
name

3 points

Answer 18

1. 18:1
   9
   Octadecenoic acid
   Oleic acid [trivial]
2. 18:2
   9,12
   Octadecadienoic acid
   Linoleic acid [trivial]

3.
18:3
9,12,15
Octadecatrienoic acid
a-Linolenic acid

Question 19

Fatty acid reactions

3 points

Answer 19

1. Fatty acids react with alcohols (compounds with -OH groups) to form esters [RCOOR] plus water

Condensation reaction

2. Fatty acids can be released from esters by a hydrolysis reaction in which the ester is split by the addition of water
3. Does not happen easily but HOH can be replaced by NaOH then have similar reaction called saponification

Question 20

Acylglycerols or acylglyerides

Answer 20

1. Most common compounds into which fatty acids are incorporated
2. The most common of all types of lipids
3. They are esters of fatty acids and glycerol – a tri-hydroxy alcohol

Question 21

how Triacylglycerol formed

2 points

Answer 21

1. Glycerol [has 3 hydroxyl groups] + 3 fatty acids [carboxylic acids]

Condensation reaction ->

Triacylglycerol = Glycerol, ester link, 3 acyl groups [R-C=O]

2. H from OH on glycerol reacting with OH on fatty acid molecule

Question 22

Triacylglycerols (TAGs)

9 points

Answer 22

1. Neutral lipids
2. The most common form of acylglycerols (mono- and di- are other forms)
3. Physical properties reflect the properties of their component fatty acids
4. Form in which lipid energy stores are deposited in adipose tissue of animals (fats) and in seeds of oilseed plants (oils)
5. Fats are solid at room temperature. Oils are liquid at room temperature

In naturally occurring TAGs the fatty acids are usually different on each of the three positions

6. Fats and oils from different sources have a characteristic distribution of fatty acids
7. Most TAGs have C16 and C18 fatty acids predominating but some notable exceptions
8. Animal fats have higher concentrations of saturated fatty acids in their TAGs than plant oils

9/ Ruminant animals (cattle, sheep) have higher concentrations of saturated fatty acids in their TAGs than non-ruminant animals

Question 23

What characteristics would make an efficient energy store?

High energy in low weight

Answer 23

long hydrocarbon chains result in higher energy/g than in carbohydrate stores (39 v 17 kJ/g dry weight); no hydration minimises associated water weight

Question 24

What characteristics would make an efficient energy store?

High energy in low volume –

Answer 24

neutral molecules pack closer together than charged molecules; no hydration minimises volume occupied

Question 25

What characteristics would make an efficient energy store? Readily stored and released from stores –

Answer 25

condensation and hydrolysis reactions readily carried out under enzyme catalysis in cells

Question 26

What characteristics would make an efficient energy store? Stores easily distinguished from surrounding material –

Answer 26

non-polar hydrophobic nature results in formation of dense lipid droplets within cells totally separate from rest of cell contents

Question 27

Characteristic which would make an efficient energy store 4 points

Answer 27

1. high energy low in weight 2. high energy low in vlume 3. readily sstored and released from stores 4. stores easily distinguished from surrounding material

Question 28

4 Chemical reactions of acylglycerols

Answer 28

Hydrolysis Saponification Iodination Hydrogenation

Question 29

Hydrolysis of acylglycerols | 3 points

Answer 29

1. the breaking of a covalent bond by the addition of water 2. Hydrolysis of acylglycerols is essential before energy can be obtained from the fatty acids 3. In biological systems the hydrolysis is catalysed by specific lipase enzymes

Question 30

Saponification of acylglycerols | 6 points

Answer 30

1. Formation of a soap by heating a triacylglycerol with alkali. 2. Fatty acids can be released from triacylglycerols by saponification. 3. This occurs when acylglycerols react with strong bases such as NaOH and KOH 4. The products of saponification are glycerol and the salts (soaps) of fatty acids 5. Soap formed are amphipathic or are amphiphiles – are both hydrophilic and hydrophobic. 6. Allows the molecules to form micelles- gives soap its cleaning properties.

Question 31

Iodination of acylglycerols

Answer 31

1. Iodine will react with the double bonds in any unsaturated hydrocarbon chains present in acylglycerols.

Question 32

Hydrogenation of acylglycerols | 3 points

Answer 32

1. Hydrogenation of unsaturated hydrocarbon chains in an acylglycerol increases the proportion of saturated fatty acids present so increasing its melting point. 2. This process is carried out industrially and is described as "Hardening" of oils. 3. It is an important process in the production of cooking fats. 4. Partial hydrogenation of vegetable oils used in cooking to improve shelf-life. - Cis double bond converted to single bond. - Also, cis double bond to trans double bond.

Question 33

Trans fatty acids linked to cardiovascular disease.

Answer 33

increase intake of trans fatty acids = increased level of triacylglycerols and LDL “bad” Cholesterol in blood and decreased levels of HDL “good “ cholesterol in blood.