Introduction to Organic and
Biochemistry
(CHE 124)
Reading Assignment
General, Organic, and Biological Chemistry: An Integrated Approach
3rd. Ed. Ramond
Chapter 11
Lipids and Membranes
Lipids
• Defined on the basis of chemical properties, not
chemical structure.
• Heterogeneous group of water insoluble
(hydrophobic) organic molecules that can be
extracted from tissues by nonpolar solvents
(e.g. chloroform.)
Functions of Lipids
Cell membranes
 phospholipids
 glycolipids
 sterols
Energy storage
 triacylglycerol or fat
 stores 2.5 X more energy than equal weight of
carbohydrates.
Cell signaling
 steroid hormones
Fatty Acids
• Long hydrocarbon chain of various lengths (C12 –
C24) and degree of saturation terminated with
carboxylic acid group.
– Saturated
* Numbering / naming carbons
• Lacking double bonds
β
α
– Unsaturated
• Contains one or more double bonds
ω
Fatty Acids (cont’)
• Double bonds may be cis or trans
16:1 cis Δ 9
16:1 trans Δ 9
Fatty Acid Length vs
Solubility
4C
CHAIN
LENGTH
INCREASES
8C
SOLUBILITY
DECREASES
12C
#C
Structure
Name
Max
solubility
4C
CH3-(CH2)2-COOH
butanoic acid
miscible
8C
CH3-(CH2)6-COOH
octanoic acid
0.0047M
12C
CH3-(CH2)10-COOH
lauric acid
0.0003M
6C
C6H12O6
Glucose
6M
Fatty Acid Nomenclature
A simplified system (Cont)
Simplified:
18 : 2 cis, cis Δ9, Δ12
Common: Linoleic acid / Linoleate
IUPAC: cis, cis-9,12-Octadecadienoic acid
Note: Always number fatty acid starting with the carboxylic
acid (COOH) carbon.
Fatty Acid Nomenclature
A simplified system
# of C
Δy …
: # of double bonds cis or trans Δ ,
x
Name this fatty acid?
Simplified:
16:0
Common: Palmitic Acid / Palmitate
IUPAC: Hexadecanoic Acid
Two Essential Fatty Acids
(Humans)
• Linoleic acid
–
–
–
–
–
18:2 cis, cis (Δ 9, 12)
cis, cis-9,12-Octadecadienoic acid
Precursor of arachidonic acid
Deficiency leads to making arachidonic acid essential
ω 6 fatty acids
• Linolenic acid
–
–
–
–
ω
6
18:3 cis, cis, cis (Δ 9, 12, 15)
cis, cis, cis-9,12,15-Octandecatrienoic acid
Precursor of other ω 3 fatty acids
Deficiency leads to:
– Decreased vision
– Altered learning behaviors
3
ω
Fatty acids
Structure
Important Facts
Formic acid / Formate
1
Acetic acid / Acetate
2:0
Propionic acid / Propionate
3:0
Butyric acid / Butanoic acid / Butanoate
4:0
Capric acid / Caprate
10:0
Lauric acid / Laurate
12:0
Palmitic acid / Palmitate
16:0
Palmitoleic acid / Palmitoleate
16:1 cis (Δ 9)
Stearic acid / Sterate
18:0
Oleic acid / Oleate
18:1 cis (Δ 9)
Linoleic acid / Linoleate
18:2 cis, cis (Δ 9, 12)
Essential
α-Linolenic acid / Linolenate
18:3 cis, cis, cis (Δ 9, 12, 15)
Essential
Arachidonic acid / Arachidonate
20:4 cis, cis, cis, cis (Δ 5, 8, 11, 14)
Precursor of Prostaglandins
Lignoceric acid / Lignocerate
24:0
Nervonic acid / Nervonate
24:1 cis (Δ 15)
Milk contains fatty acids
with 4 to 10 carbons
Palmitic acid is the precursor
of other fatty acids (except
essential fatty acids)
Structural lipids and
triacylglycerol contain fatty
acids with at least 16 carbons
• Glycerol
Phospholipids
(Phosphoglycerides)
– C-1 and C-2 esterified to the caboxyl
groups of two fatty acid; C-3 esterified to
phosphate
•
•
polar head group (e.g. phosphate)
two nonpolar tail groups (fatty acids)
– Amphipathic - molecule with both
hydrophobic and hydrophilic regions.
Glycolipids
• Substituted serine (sphingosine)
• 2 fatty acids
• carbohydrate (ie glucose).
Triacylglycerol (fats)
• glycerol
• three fatty acids
– accumulates as fat droplets in cytoplasm.
Cholesterol
•
•
•
•
•
multi-ring, nonpolar structure with a hydroxyl
component of cell membrane
precursor to steroid hormones
27 carbons – designated by a number.
Four rings A, B, C, D called the steroid nucleus
Substituted with
–
–
–
–
Hydroxyl group – may be substituted by addition of ester
Two methyl groups
A branched 8 carbon side chain
One double bond
Cholesterol - substituted
perhydrocyclopentanopenanthrene
Micelle
• Formed by ionized
fatty acids. Steric
constrants prevent
formation by
phospholipids and
glycolipids, which
preferentially form
vesicles.
Phospholipid Bilayer (Vesicle)
• Liposome (lipid vesicle) aqueous compartment surrounded
by a phospholipid bilayer
• Conatins phospholipids, glycolipids, cholesterol
Fluid Mosaic Model of Membrane
Singer and Nicolson (1972)
• Membranes are
two-dimensional
solutions of
oriented lipids and
globular proteins
(transmembrane
and peripheral)
– “rigid” Fluid that
separates two fluid
filled
compartments