Lipids are large biomolecules composed mainly of carbon and hydrogen, with small amounts of oxygen.
They are nonpolar molecules that are not soluble in water
– Are lipids that can store a great deal of energy
–Contains three fatty acids bonded to a glycerol molecule backbone (don’t worry…I’ll show you this)

1) Storage - lipids are non-polar and so are insoluble in water.
2) High-energy store - they have a high proportion of H atoms relative to O atoms and so yield more energy than the same mass of carbohydrate
3) Thermal insulation – fat conducts heat very slowly so having a layer under the skin keeps metabolic heat in.
4) Electrical insulation – the myelin sheath around axons prevents ion leakage, and increases signal speed.
1 gram of fat provides 9 kcal while 1 gram of carbohydrate
5) Waterproofing – waxy cuticles are useful, for example, to prevent excess evaporation from the surface of a leaf.
or protein provides 4 kcal
6) Hormone production – steroid hormones. Estrogen requires lipids for its formation, as do other substances such as plant growth hormones.

Fats and oils are made from two kinds of molecules:
• glycerol (a type of alcohol with a hydroxyl group on each of its three carbons) and three
• fatty acids joined by dehydration synthesis.
Since there are three fatty acids attached, these are known as triglycerides.
The main distinction between fats and oils is whether they’re solid or liquid at room temperature, and this is based on differences in the structures of the fatty acids they contain.

The “tail” of a fatty acid is a long hydrocarbon chain, making it hydrophobic.
• Hydrophobic means fear of water…so the tail end of a fatty acid is nonpolar, and will not associate with water at all.
The “head” of the molecule is a carboxyl group which is hydrophilic.
• Hydrophilic means water friendly…so the head end of a fatty acid will readily associate with water.
Fatty acids are the main component of
soap, where their tails are soluble in oily dirt and their heads are soluble in water to emulsify and wash away the oily dirt.
However, when the head end is attached to glycerol to form a fat, that whole molecule is hydrophobic.
Glycerol
Backbone

– straight molecules
–Generally solid at room temperature
–Butter, lard, grease from cooked meats
– Contain no double bonds between carbons
–Some carbon atoms linked by a “double’ covalent bond
–Generally liquid at room temperature
–EX: olive oil, fish oils
•Hydrogenated vegetable oils contain naturally unsaturated fatty acids that have been saturated artificially and are generally solid at room temperature
–EX: margarine, vegetable shortening

Phospholipids are made from
•glycerol
•two fatty acids, and (in place of the third fatty acid)
•a phosphate group with some other molecule attached to its other end.
The hydrocarbon tails of the fatty acids are still hydrophobic, but the phosphate group end of the molecule is hydrophilic because of the oxygens with all of their pairs of unshared electrons.
This means that phospholipids are soluble in both water and oil.
This becomes especially important as we learn about cells, and the structure of their membranes.

Our cell membranes are made mostly of phospholipids arranged in a double layer with the tails of the fatty acids from both layers “inside” (facing toward each other) and the heads facing “out” (toward the watery environment) on both surfaces.
O
O
CH
2
P
CH
2
O
–
+
3
)
3
Choline
O
Outside of cell
Phosphate
CH
2
O
CH
O
CH
2
Glycerol
C O C O
Fatty acids
Figure 5.13 (a) Structural formula
Inside of cell
(b) Space-filling model
Hydrophilic head
Hydrophobic tails
(c) Phospholipid symbol

Cholesterol is not a “bad guy!” Our bodies make about 2 g of cholesterol per day, and that makes up about 85% of blood cholesterol, while only about 15% comes from dietary sources.
• Cholesterol is the precursor to our sex hormones and
• Vitamin D.
Vitamin D is formed by the action of UV light in sunlight on cholesterol molecules that have
“risen” to near the surface of the skin.
Steroids may be recognized by their skeleton, consisting of three fused six-membered and one fivemembered ring
Our cell membranes contain a lot of cholesterol (in between the phospholipids) to help keep them
“fluid” even when our cells are exposed to cooler temperatures.

Waxes are widely distributed in nature .
The leaves and fruits of many plants have waxy coatings, which may protect them from dehydration and small predators.
The feathers of birds and the fur of some animals have similar coatings which serve as a water repellent.
Cuticle
Cuticle
Ocotillo Cacti

Lipoproteins are clusters of proteins and lipids all tangled up together. These act as a means of carrying lipids, including cholesterol, around in our blood.
There are two main categories of lipoproteins distinguished by how compact/dense they are.
•LDL or low density lipoprotein is the “bad guy,” being associated with deposition of “cholesterol” on the walls of someone’s arteries.
•HDL or high density lipoprotein is the “good guy,” being associated with carrying “cholesterol” out of the blood system, and is more dense/more compact than LDL.

Many plant pigments, such as anthocyanins, chlorophylls A and
B, carotenoids and xanthophylls are lipids.
Some lipid pigments can also appear in animals, like cichlids…and people.
Xanthophylls and melanins

http://www.elmhurst.edu/~chm/vchembook/547glycogen.html
www.cem.msu.edu/~reusch/VirtualText/carbhyd.htm
www.edinformatics.com/math_science/c_compounds.htm