Transcript Lipids - Alfred State College

Chapter 10.1: Storage
Lipids
CHEM 7784
Biochemistry
Professor Bensley
CHAPTER 10.1
Storage Lipids
Chapter Objectives: To understand the
– Biological roles of lipids
– Structure and properties of storage lipids
Lipids: Structurally Diverse Class
• Low solubility in water
• Good solubility in nonpolar solvents
Classification of Lipids
Based on the structure and function:
1. Lipids that contain fatty acids
(complex lipids):
Storage lipids and membrane lipids
2.
Lipids that do not contain fatty
acids:
Cholesterol, terpenes, …
Lipid Subclasses
Fatty Acids
• Carboxylic acids with hydrocarbon chains containing from 4
to 36 carbons
• Almost all natural fatty acids have an even number of
carbons
• Most natural fatty acids are unbranched
• Saturated:
• Monounsaturated:
• Polyunsaturated:
Common Saturated Fatty Acids
common name
IUPAC name
12:0
14:0
laurate
myristate
dodeconoate
tetradeconoate
melting point
(Co)
44
52
16:0
18:0
20:0
22:0
palmitate
stearate
arachidate
behenate
hexadeconoate
octadeconoate
eicosanoate
docosanoate
63
70
75
81
24:0
lignocerate
tetracosanate
84
Common Unsaturated Fatty Acids
common name
IUPAC name
melting
point
(Co)
16:0
palmitate
hexadeconoate
63
16:1 D9
palmitoleate
cis-D9-hexadeconoate
-0.5
18:0
stearate
octadeconoate
70
18:1 D9
oleate
cis-D9- octadeconoate
13
18:2 D9,12
linoleate
cis-D9,12- octadeconoate
-9
18:3 D9,12,15
linolenate
cis-D9,12,15- octadeconoate
-17
20:0
arachidate
eicosanoate
75
20:4 D5,8,11,14
arachindonate
cis- D5,8,11,14-eicosatetraenoate
-49
Physical Properties and Conformation
of Saturated Fatty Acids
• Solubility decreases as the chain length increases
• Melting point increases as the chain length
increases
• The saturated chain tends to adopt extended
conformations
• The double bonds in natural unsaturated fatty
acids are commonly in cis configuration
• This introduces a kink in the chain
Melting Point and Double Bonds
• Saturated fatty acids pack in a fairly orderly way
– extensive favorable interactions
• Unsaturated cis fatty acid pack less regular due to
the kink
– Less extensive favorable interactions
• It takes less thermal energy to disrupt disordered
packing of unsaturated fatty acids:
– unsaturated cis fatty acids have a lower melting point
Melting
Points of
Fatty
Acids
18:0
70o C
18:1
13o C
18:3
-17o C
Trans Fatty Acids
• Trans fatty acids form by partial dehydrogenation
of unsaturated fatty acids
• A trans double bond allows a given fatty acid to
adopt an extended conformation
• Trans fatty acids can pack more regularly, and
show higher melting points than cis forms
Triacylglycerols (fats and oils)
• Majority of fatty acids in biological systems are found in
the form of triacylglycerols
• Triacylglycerols are the primary storage form of lipids
(body fat)
• Triacylglycerols are less soluble in water than fatty acids
due to the lack of charged carboxylate group
• Triacylglycerols are less dense than water: fats and oils
float
Waxes
• Waxes are esters of long-chain saturated and
unsaturated fatty acids with long-chain alcohols
• Insoluble and have high melting points
• Beeswax is a mixture of a large number of lipids,
including esters of triacontanol, and a long-chain alkane
hentiacontane