Lipids

Question 1

how are lipids defined

Answer 1

by their common chemical property: hydrophobicity

Question 2

how do we dissolve lipids

Answer 2

in organic solvents - not in water

Question 3

Biological functions of lipids

Answer 3

• energy storage (triacylglycerols)
• structural elements of membranes (phospholipids and sterols)
• signal transduction
• enzyme cofactors
• vitamins (A, D, E, K)
• light-absorbing pigments

Question 4

glycolipids

Answer 4

contain both sugar and lipid portions
- important constituents of cell membranes

Question 5

lipoproteins

Answer 5

contain protein and lipid portions
- associated with cardiovascular health and disease

Question 6

what are Fatty acids

Answer 6

carboxylic acids with large hydrocarbon chains (4-36 C)

Question 7

saturated fatty acids

Answer 7

• have no double bonds between carbons
• maximum number of hydrogens

Question 8

unsaturated fatty acids

Answer 8

• one or more double bonds between carbons

Question 9

naming fatty acids

Answer 9

• specify number of carbons in the chain followed by the number of double bonds (ex 18:2)
• the position of double bond/s is specified relative to carbonyl carbon using subscripts following delta

Question 10

alternative convention for naming fatty acids

Answer 10

• specify the position of double bond relative to methyl carbon following omega

Question 11

features of commonly occurring fatty acids

Answer 11

• even number of carbons
• unbranched
• double bonds found in cis config
• bonds in PUFA’s are methylene bridged, not conjugated
• bonds pattern is double-single-single-double since they are separated by methylene carbons

Question 12

commonly occurring fatty acids

Answer 12

12C = laureate
14C = myristate
16C = palmitate
18C = Stearate
20C = arachidate

Question 13

trans fatty acids

Answer 13

a trans double bond gives the fatty acid an extended formation
- synthetic
- negative effects on cardiovascular health
- partial hydration makes objects that are usually liquid at room temp solid

Question 14

solubility and melting point of saturated fatty acids

Answer 14

• since saturated chains have extended configuration, there pack tighter and have a higher melting point
• as chain length increases melting point increases and solubility decreases

Question 15

melting point and double bonds

Answer 15

• unsaturated fatty acids pack less orderly due to kinks by cis bonds
• melting temperature is MUCH lower than saturated
• trans fatty acids have higher melting points than cis since they have extended configuration

Question 16

derivatives of fatty acids

Answer 16

carboxylic acid + alcohol = ester
carboxylic acid + acid = anhydride

Question 17

Tracylglycerols (TAGs)

Answer 17

• majority of fatty acids in biological systems
• formed by linking 3 fatty acids to a glycerol through ester linkages
• highly hydrophobic
• melting points depend on length and degree of saturation

Question 18

simple vs mixed TAGs

Answer 18

simple: same fatty acid in all 3 tail
positions
mixed: 2 or 3 different fatty acids in tail position

Question 19

glycerophospholipids

Answer 19

• primary constituents of biological membranes
• carbon atoms 1 and 2 of glycerolize esterified to 2 fatty acids
• carbon 3 is attached to a highly polar or charged group through a phosphodiester linkage
• this allows them to form lipid bilayers

Question 20

phosphatidylcholine (lecithin)

Answer 20

represents a class of lipids with a choline X group

Question 21

lipids when dispersed in water

Answer 21

micelles: simplest aggregate, single-layer spherical structure
bilayer: 2 layers with hydrophobic tails facing inward, fundamental structure of cell membrane
vesicles: bilayer which folds back on itself to give a spherical structure

Question 22

analysis of lipids

Answer 22

• lipids are separated based on their polarity in TLC
• less polar lipids more farther than more polar lipids
• separated fatty acids can be identifies through mass spectrometry