1. GUTS Session on Lipid Structure & Nomenclature
Get UP To Speed (GUTS) Session on Lipids
A primer on lipid structure, nomenclature, and function
See also the GUTS session on Lipids notes (.doc) - self-assessment exam - additional lipid information
Dr. Arrel Toews (say Tavz, like “waves”)
420 ME Jones Building

2. Lipids
Definition: biomolecules that are overall hydrophobic - very non-polar insoluble in water/aqueous solutions (cellular environment) - soluble in “organic” (non-polar) solvents (CHCl3-MeOH) - operational rather than structural definition
(water-fearing)
- contrast this with definitions for: proteins nucleic acids carbohydrates

3. Lipid Functions
- energy source (dietary triglycerides) - energy stores (adipose tissue triglycerides)
- triglycerides are completely hydrophobic highly reduced (energy-rich) compact, efficient energy storage
- membranes – amphipathic lipids (both hydrophobic and hydrophilic portions) phospholipids sphingolipids cholesterol
- signaling molecules 2nd messenger systems; eicosanoids; steroid hormones
- fat-soluble vitamins: A (vision), D (bones/teeth), E (anti-oxidant; live forever), K (blood clotting)
Fatty acids are basic building block of most lipids

4. Structure and nomenclature of fatty acids
Long-chain carboxylic acids; building blocks of most lipids
H H H H H H H H H H H H H H H H H O l l l l l l l l l l l l l l l l l ll H―C―C―C―C―C―C―C―C―C―C―C―C―C―C―C―C―C―C-O l l l l l l l l l l l l l l l l l H H H H H H H H H H H H H H H H H *
O ll CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2C-O- *
O ll C-O- *
Stearic acid CH3(CH2)16COOH
Systematic: octadecanoic acid
Shorthand: 18:0 (18C, no double bonds)
*All fatty acids ionized at physiological pH; pKa <5

5. Structure and nomenclature of fatty acids
Linoleic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
Systematic: cis, cis 9,12-octadecadienoic acid
Shorthand: 18:26
This is shorthand for a fatty acid with 18 carbons and 2 double bonds. The 6 indicates the double bond closest to the methyl end is 6 carbons from the  end.
If more than one double bond, the configuration is always “methylene-interrupted” (-CH=CH-CH2-CH=CH-) with cis double bonds. Always 3C between C=C bonds
So - the term 18:26 completely defines the formula and structure of linoleic acid

6. Structure and nomenclature of fatty acids
 
“biochemists”
O ll CH3―(CH2)n―CH2―CH―C-O- 
no matter how long
generic fatty acid
18 or whatever
“systematic”
-designation important in nomenclature “-oxidation” of fatty acids
CH3(CH2)14COOH CH3(CH2)5CH=CH(CH2)7COOH CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH CH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH CH3(CH2)CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)2COOH
Try this at home: write shorthand names for the FA below
Write the chemical formulas for 18:19 and 20:53

7. Fatty Acids: long-chain carboxylic acids
COOH 3 HC H
cis-fatty acid
trans -
fatty acid
saturated fatty acid
O ll *really C―O-
usually attached to glycerol as PL or TG
Virtually all natural C=C double bonds are cis
“kinks” – less packing – more fluid GOOD for membranes
trans-FA are BAD! – no kinks, pack tightly;  LDL;  HDL (partially hydrogenated vegetable oils, Crisco, margarine)

8. Physiological functions of lipids – a problem
hydrophobicity (long chain length)
and
fluidity (liquid at body temperature)
both vital required biophysical properties
- cell membranes
- storage depots of energy (adipose tissue)
But melting point increases with chain length
So FA long enough to be hydrophobic are solids! (mp is above body temp)
How does Mother Nature handle this??

9. Melting points of fatty acids90
18C fatty acids 80 70
Saturated fatty acids
Stearic acid (18:0) 60 50 40
Body temperature
Melting temperature (°C) 30 20
Oleic acid (18:1) 10
18:4 -57C
Linoleic acid (18:2)
-10
— Linolenic acid (18:3)
-20 2 4 6 8 10 12 14 16 18 20 22 24
Number of carbon atoms

10. Physiological functions of lipids
The fatty acid composition of membrane lipids and adipose tissue triglycerides - chain length - degree of unsaturation is carefully regulated to maintain the appropriate fluidity

11. Most of the fatty acid in the body is esterified
– much of it as triglyceride (mostly in adipose tissue) – also lots in phospholipids (major components of membranes)
Fatty acid composition is regulated to maintain correct fluidity (both TG and PL) critical to biological function
O ll CH2OC
fatty acid
glycerol
O ll CHO C
Triglyceride energy source storage form
O ll CH2OC

12. Phospholipids – vital components of membranes
glycerol backbone (like TG) - 2 FA in ester linkages - phosphate + X (choline, ethanolamine, serine, inositol)
amphipathic (amphi = both)
polar head
long hydrophobic tail
e.g., choline+
F A T T Y A C I D
GLYCEROL
F A T T Y A C I D
Remember kinks in cis-double bonds of unsat’d FA P
THE defining components of biological membranes - make lipid bilayers (2 molecules thick)

13. Phosphatidylcholine (PC)
aka lecithin a prominent phospholipid major membrane component involved in cholesterol handling too
glycerol
2 long-chain fatty acids
Choline (polar “X”)
phosphate
FA heterogeneity means many molecular species of PC

14. 2nd messenger signaling systemsO ll CH 2 - C
fatty acid P l 3 HN +
ethanolamine
Phosphatidylethanolamine (PE)
membranes
2nd messenger signaling systems

15. (more on these in “Complex CH2O” GUTS session)
Sphingolipids
Structures and properties are generally similar to phospholipids (amphipathic)
Phospholipids
long hydrophobic tail
polar head
sugar(s) O
Long-chain amino alcohol (sphingosine)
Glycosphingolipids
(usually)
F A T T Y A C I D
(more on these in “Complex CH2O” GUTS session)

16. Hydrophobic tails hide from water
Amphipathic nature of PL and sphingolipids is vital to life; makes membranes
water
Lipid bilayer
water
Polar head
Micelle
Hydro- phobic tail
Phospholipid or glycolipid
Hydrophobic tails hide from water
Lots more on this in Dr. Jacobson’s Membranes GUTS lecture

17. Cholesterol - rigid ring structure - “a little bit” amphipathic
polar
- “a little bit” amphipathic
Cholesterol
- rigid ring structure
- membrane component (affects fluidity)
- lipid transport in blood (atherosclerosis, &c)

18. Vocabulary – do you know the meaning of the following terms?
lipid hydrophobic vs hydrophilic amphipathic fatty acid
saturated vs unsaturated FA
cis vs trans C=C double bonds shorthand nomenclature for FA triglyceride (and mono- and diglyceride) phospholipid sphingolipid cholesterol