Lipids 1Steven E. Massey, Ph.D.

Associate ProfessorDepartment of Biology

University of Puerto Rico – Río Piedras

Office & Lab: Bioinformatics Lab

NCN343BTel: ext. 7798

E-mail: stevenemassey@gmail.com

Lipids are diverse compounds with the common feature that they are insoluble in water

They include oils, wax and fat

They have two main roles 1) as energy storage compounds and 2) comprising membranes

Additional roles include:

cofactors (of enzymes)pigments (that absorb light)hormoneselectron carriersemulsifying agentsintracellular (secondary) messengers

The simplest lipids are composed of three fatty acids condensed to form three ester bonds with glycerol

These are called triacylglycerols

Fatty acids are carboxylic acids with long hydrocarbon chains usually 4 to 36 carbon atoms long

Glycerol has three carbonatoms, with a hydroxyl group on each carbon :

Tricacylglycerols are insoluble with water and less dense - this is why oils float on water

They are mostly found in vegetable oil and animal fats,functioning as energy storage compounds

An example of a triacylglycerol from beef fat

Triacylglyerols are energy rich and compact and so ideal for energy storage. In vertebrates they are common in adipose tissue in adipocytes.

Excessive calorific intake leads to increased synthesis of these storage fats, leading to obesity

Adipocytes from guinea pig, full of fat droplets.These are for energystorage and also insulation

Cotyledon from an Arabidopsis seed showing protein bodies (dark) andoil droplets (light). The oils provideenergy for the growing seed

Fatty acid numbering conventions

The first carbon of the carboxyl group is number 1

There may be double bonds between carbon atoms; these are called unsaturated bonds

(this refers to the fact that not all the bonds are saturatedwith hydrogen)

A fatty acid with a single double bond (ie. a monounsaturatedfatty acid) is named by length : number of double bonds eg. 18:1

The position of the double bond is indicated by a ∆ and itsposition from carbon number 1 eg. 18:1 (∆9)

A polyunsaturated fatty acid (PUFA) has more than one double bond. In this case the type of PUFA is named from the opposite end (the Ω carbon) eg. omega 3 or omega 6

Examples of:

a) a mono unsaturated fatty acid

b) a polyunsaturated fatty acid

The most common fatty acids have an even number of carbon atoms ranging from 12 to 24 in length

The even number results from the mode of synthesis, fromprecursors with an even number of carbon atoms (acetyl coA and malonyl coA)

The double bonds have common positions eg. in monounsaturated fatty acids the double bond is most often between C-9 and C-10

In PUFAs they are almost never alternate, like this:

-C=C-C=C-C-

But have at least two single bonds between them, like this:

eg. -C=C-C-C=C-

Physical differences between fatty acids

The longer the hydrocarbon chain, the higher the melting temperature of the fatty acid

The greater the number of double bonds, the lower the melting point; this is because they are relatively disordered

due to kinks in their hydrocarbon chains

This is the essential difference between fats and oils

Examples of:

a) a saturated fatty acid

b) an unsaturated fatty acid

c) saturated fats pack in an orderly fashion

d) unsaturated fats are disordered

Saturation is a method to raise the melting temperature by hydrogenation ie. saturating all the carbon bonds withhydrogen

This uses hydrogen and a catalyst to react with a fat or oil

The process produces single bonds and also convert cis double bonds to trans

This is used in the food industry for making oils solid atroom temperature

Naturally occurring oils and fats vary in the lengths of their carbon chains and degree of saturation – an oil issimply a liquid fat

Sperm whales possess an amazing adaptation called a 'spermaceti organ'. This contains unsaturated triacylglycerols that are liquid at the surface, but which freeze at colder temperatures, increasing its density and becoming a buoyancy device

Omega 3 fatty acidsAn omega 3 fatty acid has a double bond at carbon 3 from theomega carbon and an omega 6 fatty acid has a double bond atcarbon 6

Humans cannot synthesize alpha-linolenic acid (ALA,18:3) which is a precursor of eicosapentaenoic acid (EPA, 20:5) and docosahexanoic acid (DHA, 22:6)

These function in cellular physiology and in the brain

So, they must all ultimately be obtained from the diet

The optimal ratio in the diet of omega-6 to omega-3 is 1:1 to 4:1Most North Americans only get 10:1 to 30:1 !!!!!!!

The brain is 8 % omega 3 fatty acids...... Omega 3s also reduce cardiovascular disease

ALA must be obtained from vegetables and wild animalswhich are uncommon in the western diet

In addition, the western diet has an excess of omega 6

A solution is to take omega 3 (fish) supplements:

WaxesWaxes are esters of a long chain (C14 to C36) fatty acid and a long chain (C16 to C30) alcohol

They are used for energy storage, for water repulsion andprotection against pathogens / herbivores

Waxes have a variety of uses in cosmetics, pharmaceuticals and other industries

Lanolin from lambs wool, beeswax from bee's hives and spermaceti wax have all been used

Triacontanoylpalmitate is an ester of palmitic acid and triacontanol. It is a major component of beeswax, which isused to make a bee hive

Membrane lipidsMembranes are mostly composed of lipids: the lipids have a structural role

The lipids are amphipathic - charged at one end and hydrophobic at the other. This property is important in the formation of a lipid bilayer (more later !)

There are four categories of membrane lipids: phospholipidsglycolipidsarchaeal ether lipidssterols

They have glycerol or sphingosine as their backbone (pink),long chain alkyl groups are in yellow and a polar head group (blue)

Categories of storage and membrane lipids

Glycerophospholipids are also called phosphoglycerides

These have two fatty acids attached by an ester linkage to the first and second carbons and a phosphate on the third

The first fatty acid is usually saturated, while the secondis unsaturated :

X can be just a Hydrogen, or a variety of compounds such as ethanolamine and choline

Some glycerophospholipids have ether linked fatty acids eg. plasmalogen, which is enriched in the heart membranes

Ether lipids are found in the membranes of the heart, ciliates and halophilic bacteria

Their function is not clear

Platelet activating factor is another ether lipid that acts as a molecular signal. It is released from leukocytes and stimulates platelet aggregation. It is also involved in inflammation and the allergic response

Membrane lipids in plantsGalactolipids dominate membranes in plant cells (not phospholipids)

These have 1-2 galactose residues connected to the 3rd carbon of glycerol instead of a phosphate, so they are a type of glycolipid

They are enriched in thylakoid membranes

Sulfolipids are also located in thylakoid membranes

These have a sulfonated glucose residue connected to the 3rd carbon of glycerol. These are also a type of glycolipid

Phosphate is often limiting in plant soil, and this may be the reason why galactolipids and sulfolipids are used

galactolipid

galactolipid

sulfolipid

Lipids commonly found in plant thylakoid membranes

Archaeal membrane lipidsArchaeal membrane lipids have long hydrocarbon chains and a polar structure, similar to phospholipids

Ether linkages are used instead of ester linkages, maybe because they are more stable

UPR astrogenomics / astrobiology team

Collaboration between Oscar Resto (Department of Physics) and the NASA Rocksat team, and the Bioinformatics Lab

Objective : to isolate microbes from about the Karman Line eg. Outer Space