Lipids
• Lipo: fat
• varied structures (unlike proteins and sugars)
• Insoluble in water (are either hydrophobic or amphipathic)
• Soluble in organic solvents and other lipids
Function of lipids
• Storage of energy (fat)
• Structural (cellular membranes, polymer of lipids)
• Protective molecule (wax)
• Hormones
Fatty acids
• Carboxylic acids with long carbon chains
• This carboxylic acid does not form H-bonds
(fatty acids interact through hydrophobic interactions)
• pKa of this carboxylic acid is 4-5, so deprotonated in body
• 12-20 Carbons compose chain (“tail”)
(this includes the carboxylate C)
• Generally fatty acids have an even number of carbons
• Are amphipathic (both polar and nonpolar)
A fatty acid may or may not contain double bonds
•_____________:
- every C in tail has four atoms attached
• _____________:
- at least one double bond in the tail
- All natural double bonds in fatty acids are cis
- The double bond leads to a bend in the C tail
Chemistry C483
Fall 2009
Prof Jill Paterson
22-1
Structural rules of fatty acids
• Usually even number of C
• Always unbranched
• Most C-C bonds are single, although may have double bonds
• Double bonds in natural human fatty acids are always cis
• If there is more than 1 double bond, these bonds are not conjugated, but are separated by at
least 1 methylene group
Fatty acids vary in chain length and degree of saturation
Saturated fatty acids
Unsaturated fatty acids
• pack closely together
• Do not pack as closely as saturated fatty acids
• less fluid
• more fluid than saturated
• higher melting temps
(b/c more energy required to
break hydrophobic interactions)
• lower melting temps than saturated
(hydrophobic interactions not as strong
due to bends)
• Generally solid at RT
• Generally liquid at RT
Chemistry C483
Fall 2009
Prof Jill Paterson
22-2
Chain length and degree of saturation:
• affect melting point
• affect fluidity
Nomenclature
Lipids have common names.
You should know, and be able to draw:
1.
2.
3.
•
•
•
•
#C:# double bonds∆a,b,c
Arachidonic acid: 20:4∆5,8,11,14
#C is from the carboxyl end and includes the carboxyl C (#1)
Double bonds occur after the indicated number
-for Arachidonic acid, double bonds are between:
abbreviated
symbol
Chemistry C483
Fall 2009
Prof Jill Paterson
22-3
Draw structures
Triacylglycerols
• Note these structures are neutral
• TAGs are nonpolar, hydrophobic
Chemistry C483
Fall 2009
Prof Jill Paterson
22-4
Oils
• Usually come from plants
• Contain more unsaturated fatty acids
• Liquid at RT
• Coconut oil is the exception
Fats
• Usually come from animals
• Contain more saturated fatty acids
• Saturated fats lead to heart disease
-this is why people are frying in vegetable oils
• Fats are stored in adipocytes
-oily droplets in cytoplasm
• However, fats have more energy!
-they are highly reduced, less hydrated, more to oxidize and give energy
Trans-fats
• Reduced corn oil. This leads to saturation of db. Go from a solid to a “less” solid
• Also produce trans fatty acids
• Trans fatty acids lead to increased LDL (bad cholesterol) and decreased HDL (good cholesterol)
Phospholipids (glycerophospholipids or phosphoacylglycerols, or phosphoglycerides)
Looks like a TAG, except
phosphatidic acid (PA) replaces
1 fatty acid
Chemistry C483
Fall 2009
Prof Jill Paterson
22-5
PA is further esterified
Different headgroups lead to different properties
Chemistry C483
Fall 2009
Prof Jill Paterson
22-6
Phospholipids are amphipathic
• PLs have a hydrophobic tail region and a hydrophilic headgroup
• Different from TAGs which are hydrophobic (no polar regions)
Phospholipases
• Phospholipases are enzymes that degrade phospholipids
Chemistry C483
Fall 2009
Prof Jill Paterson
22-7
Snake venom
• The predominate poisons of snake venom are various phospholipids
• Diamondback venom is phospholipase A2
• If 1 tail component is removed, you are left with a “one-legged” PL
• This one-legged PL is called a lysolecithin
• Lysolecithin acts as a _______________ and dissolves cellular membranes
Sphingolipids
The glycerol backbone of a TAG is replaced with sphingosine
The glycerol backbone of a TAG is replaced with sphingosine
1 fatty acid chain is replaced with various headgroups
Headgroup
Chemistry C483
structure of headgrp
Fall 2009
name of sphingolipid
Prof Jill Paterson
22-8
• Amphipathic like PL
• Sphingomyelin
-A major membrane lipid
-Insulator of nerve axons
- Found in myelin sheaths
- Effected in MS (through unknown mechanism)
• Cerebrosides and gangliosides (sugar headgroups)
-Found in brain (hence its name) and nervous system
- If not degraded properly:
Chemistry C483
Fall 2009
Prof Jill Paterson
22-9
Steroids
• Fused ring (rigid) structure
• No ester linkages (in contrast to all other lipids)
• Includes cholesterol and hormones
Cholesterol
• Found in membranes
• Never found in plants
• Amphipathic! That –OH group adds some polarity!
• Starting point for hormone synthesis
Chemistry C483
Fall 2009
Prof Jill Paterson
22-10