1. Chapter 21: Lipids
Chem 104
K. Dunlap

2. Lipids
• like CHO, lipids are compose of carbon, hydrogen
and oxygen
• unlike, CHO they do not contain multiple hydroxyl
groups for hydrogen bonding, and therefore are
insoluble in water
• Lipids include a large variety of molecules:
- fatty acids
- triglycerides
- waxes
- eicosanoids
- steroids
- fat soluble vitamins

3. General info on Lipids…
• insoluble in water
• wide range of functions: insulate and protect internal organs,
signaling molecules, energy
• most efficient form in which energy is stored in the body
• fats in animals absorb and sequester nonpolar contaminants,
such as DDT, PCBs, organomercury
•excess glucose, lipids and proteins are stored in adipose cells

4. Lipids: diverse class of molecules
1) Energy and storage – fatty acids,
triacylglycerides, waxes
2) Membrane structure – phospholipids,
glycolypids, sterols
3) Signaling, cofactors and pigments –
Eicosanoids, sterols, fat soluble vitamins

5. Energy & storage Lipids
•
Fatty Acids
•
Triacylgerols
•
Waxes

6. Fatty Acids
• long chain, even number carboxylic acids, typically
between 12 and 26 carbons
• Saturated fatty acids have no double bonds
• Unsaturated fatty acids have at least one double
bond

7. Unsaturated Fatty Acids
• Most naturally occurring fatty acids are in the cis
form
• causes a bend in the molecule
• chains cannot pack tightly, and therefore are less
dense, with lower melting points

8. Cis, Trans, & Saturated Fatty Acids

9. Common Fatty Acids

10. Formation of Triglycerides
• glycerol backbone, with three fatty acids, joined by ester
linkages
• The fatty acids that compose the triglyceride affect their
properties, such as melting point
• Fats have FAs with fewer double bonds
• Oils have FAs with more double bonds

12. Triglycerides
• The lower melting points of triglycerides rich in
unsaturated fatty acids are related to
differences in their three-dimensional shape.
– Hydrocarbon chains of saturated fatty acids can lie
parallel with strong London dispersion forces
between their chains; they pack into well-ordered
forms and melt above room temperature
– Because of the cis configuration of the double
bonds in unsaturated fatty acids, their hydrocarbon
chains have a less ordered structure and London
dispersion forces between them are weaker; these
triglycerides have melting points below room
temperature.

13. Triacylglycerols: stored fat
• Insulation - seals, walruses, penguins
• Energy – Hibernation
13

14. Hydrogenation
• Hardening: reduction of some or all of the
carbon-carbon double bonds of an
unsaturated triglyceride using H2/metal
catalyst.
– In practice, the degree of hardening is carefully
controlled to produce fats of a desired consistency.
– The resulting fats are sold for kitchen use (Crisco,
Spry, Dexo, and others).
– Margarine and other butter substitutes are
produced by partial hydrogenation of
polyunsaturated oils derived from corn,
cottonseed, peanut, and soybean oils.

15. Hydrogenation of Unsaturated
Fats
• Oils can be converted to semi-solids through
hydrogenation that converts the double bonds to
single bonds
• In the process, some double bonds are converted
to trans form

16. Complex Lipids
• Phospholipids
– contain an alcohol, two fatty acids, and a
phosphate ester.
– In glycerophospholipids, the alcohol is glycerol.
– In sphingolipids, the alcohol is sphingosine.
• Glycolipids
– Complex lipids that contain a carbohydrate.

17. Complex Lipids
• Figure 21.1 Schematic diagram of simple and
complex lipids.

18. Membranes
• Complex lipids form the membranes around
cells and small structures within cells.
• In aqueous solution, complex lipids
spontaneously form into a lipid bilayer, with a
back-to-back arrangement of lipid monolayers.
– Polar (hydrophilic) head groups are in contact with
the aqueous environment.
– Nonpolar (hydrophobic) tails are buried within the
bilayer
– The arrangement of hydrocarbon tails in the
interior can be rigid (if rich in saturated fatty acids)
or fluid (if rich in unsaturated fatty acids).

19. Lipids in Membranes: Fluid Mosaic Model
• Polar heads and nonpolar tails

20. Storage vs. Structural lipids in membranes
20

21. Glycerophospholipids
• Polar or charged
group is
attached to the
third carbon of
glycerol
– Basis for
nomenclature
• Most abundant
lipid in biological
membranes
21

22. Sphingolipids
• One fatty acid joined to
sphingosine
• Polar head group
• Sphingomyelin,
Glycosphingolipids,
Gangliosides
• Sphingomyelin - animal
cells, especially myelin
• Some involved in signal
transduction & cell surface
recognition
22

23. Glycosphingolipids:
determinants of the blood groups
23

24. Cholesterol
• Cholesterol is the major sterol in animal
tissues
– It is a component in plasma membranes in all
animal cells.
– It is the precursor of all steroid hormones, some
vitamins and bile acids.

25. Steroids
• Steroids: a group of plant and animal lipids
that have this tetracyclic ring structure.

26. Steroids
• cholesterol, bile acids,
vitamin D, and many
hormones
• Oxidized sterols
• Lipid soluble and
enter cells
• Bind nuclear
receptors and alter
gene expression
and metabolism

27. Cholesterol
• Cholesterol is the most abundant steroid in the
human body, and also the most important.
– It is a component in plasma membranes in all
animal cells.
– It is the precursor of all steroid hormones and bile
acids.

28. Lipoproteins
• Cholesterol, along with fats, are transported by
lipoproteins

29. Lipoproteins
• Figure 21.5 Schematic of a low-density
lipoprotein.

30. Cholesterol
•is the most abundant steroid and is the starting
material for all other steroids
• present in animal fats
• major factor in the development of atherosclerosis
• transported by lipoproteins:
VLDL (very low density lipoproteins)- transport
triglycerides
LDL (low density lipoproteins)- transport cholesterol
from liver to tissues
HDL (high density lipoproteins)- transport cholesterol
from tissues to the liver for elimination

31. Bile Salts
• Bile salts, the oxidation products of
salts
cholesterol.
– synthesized in the liver, stored in the gallbladder,
and secreted into the intestine where they emulsify
dietary fats and aid in their absorption and
digestion

32. Fats
Essential Fatty acids:
Omega-3
EPA, DHA, linoleic
• recommended 30% of diet
-10% monounsaturated
-10% saturated
-10% unsaturated
Omega-6
Arachidonic acid, α-linolenic
• EPA, DHA, AA are 20
carbon hormone-like
fatty acids that play an
important part in the
immune function

33. Omega-3 Fatty Acids
Eicosapentaenoic acid (20:5ω-3)

34. Prostaglandins & Leukotriene
• are not stored in tissues as such, but are
synthesized from membrane-bound 20-carbon
polyunsaturated fatty acids in response to
specific physiological triggers.
– One such polyunsaturated fatty acid is arachidonic
acid.

35. Eicosanoids: paracrine hormones
Regulate synthesis of cAMP
production  fever, pain,
blood flow, and uterine
contraction
Produced by
platelets,
important in
clotting and
blood flow
Inflammation,
asthma, allergy
• Derived from the 20 carbon polyunsaturated fatty acid
(arachidonic acid)
• Involved in reproduction, inflammation, fever and pain
• 3 classes: Prostaglandins, thromboxanes, leukotrienes
35

36. Phospholipid membrane
Phospholipase A2
O
HO
Eicosapentaenoic acid
Arachidonic
Cyclooxygenases (COX)
Prostaglandins (PG)
&
Thromboxanes (TX)
Lipoxygenases (LOX)
Leukotrienes
-poor substrate for cyclooxygenases
-gives rise to series 5 leukotrienes

37. More on Lipids……
• fats insulate and protect internal organs
• most efficient form in which energy is stored in
the body
-9 kcal/ gram as opposed to 4
• fats in animals absorb and sequester nonpolar
contaminants, such as DDT, PCBs,
organomercury
• excess glucose, lipids and proteins are stored in
adipose cells

38. Endocrine Disruptors
•Hormones are substances
produced in specialized
glands such as the pituitary,
thymus, hypothalamus,
thyroid, adrenals, pancreas,
gonads which make up the
endocrine system
• direct and control
reproduction, prenatal
development, growth, and
many regulatory processes
• endocrine disruptors refer to
contaminants that mimic or
interfere with the function of
hormones: PCB, dioxin, DDT

39. 1. What is a polyunsaturated fatty acid?
2. What happens when a polyunsaturated FA is
hydrogenated? What happens to the physical properties of
the oils?
3. What molecules react to form a triglyceride?
4. What is an endocrine disruptor?

40. This membrane lipid is classified as a
____________?

41. 5. In contrast to water-soluble vitamins, which must be part of
our daily diet, fat-soluble vitamins can be stored in the body in
amounts sufficient for many months. Suggest an explanation
for this difference.
6. The melting points of a series of 18-carbon fatty acids are:
stearic acid, 69.6 C°; oleic acid, 13.4 C°; linoleic acid, -5 C°;
and linolenic acid, -11 °C. What structural aspect of these
18-carbon fatty acids can be correlated with the melting
point?

42. What are some important biochemical
roles of lipids in Alaska?