Chapter 9: Lipids and Biological Membranes

-mostly hydrophobic -The functions of lipids include storing energy, signaling, and acting as structural components of cell membranes. -Lipids are molecules that contain hydrocarbons and make up the building blocks of the structure and function of living cells lipids are not polymeric. Lipids exhibit greater structural variety than the other classes of biological molecules. However, they do aggregate, and it is in this state that they perform their central function as the structural matrix of biological membranes.

-Not soluble in water -Soluble in organic solvents such as chloroform and methanol

Fats, oils, certain vitamins and hormones, and most nonprotein membrane components are lipids.

Hence, they are easily separated from other biological materials by extraction into organic solvents. They can then be separated chromatographically and identified by mass spectrometry according to their masses and characteristic fragmentation patterns

1.Fatty acids-a common fuel 2.Triacylglycerols-storage form of fatty acids 3.Phospholipids-membrane lipids 4.Glycolipids-membrane lipids composed in part of carbohydrates 5.Steroids-polycylic hydrocarbons with a variety of functions

Fatty acids are carboxylic acids with long-chain hydrocarbon side groups carboxylic acid at one end and a methyl group (CH3) at the other end fatty acids may be saturated or unsaturated Make up major components of the various lipids most basic lipid

Hydrocarbon Chains/Chain Length also degree of unsaturation

In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group attached to an R-group. The general formula of a carboxylic acid is R−COOH Found in Fatty acids

-Esterified form

-a chemical compound produced by a reaction between an acid and an alcohol with the elimination of a molecule of water

16-18 Most fatty acids have an even number of carbon atoms because they are biosynthesized by the concatenation of C2 units C16 and C18 species: palmitic, oleic, linoleic, and stearic acids.

unsaturated (contain double bonds) and are often polyunsaturated (contain two or more double bonds).

-unsaturated means it contains one double bond -polyunsaturated means it contains 2 or more double bonds both unsaturated and polyunsaturated are rigid due to cis transfiguration -saturated has no double bonds and is super flexible can assume a wide range of conformations because there is relatively free rotation around each of their C—C bonds.can assume a wide range of conformations because there is relatively free rotation around each of their C—C bonds.

methyl group=CH3 for fatty acids methylene group=CH2 to separate the double bonds in polyunsaturated fatty acids

the first double bond of an unsaturated fatty acid commonly occurs between its C9 and C10 atoms counting from the carboxyl C atom. This bond is called a Δ9 - or 9-double bond. In polyunsaturated fatty acids, the double bonds tend to occur at every third carbon atom (e.g., —CH-CH-CH2—CHCH—)

at least one methylene group (-CH2-)

cis -puts a rigid 30° bend in the hydrocarbon chain. -pack together less efficiently than saturated fatty acids. -The reduced van der Waals interactions of unsaturated fatty acids cause their melting points to decrease with the degree of unsaturation

-only single bonds, tightly packed fully reduced or “saturated” with hydrogen are highly flexible molecules that can assume a wide range of conformations because there is relatively free rotation around each of their C—C bonds.

melting point increases as molecular mass increases

the longer the side chain, the lower the fluidity and the higher the melting point -Longer hydrophobic tails allow more hydrophobic interactions

-The presence of cis bonds enhances the fluidity and decreases the melting point of fatty acids. -The cis double bond gives the hydrophobic tail a “kink” and prevents optimal hydrophobic interactions between the tails

short chain length and present of cis bonds

generally, unsaturated fatty acids have lower mp than saturated fatty acids

-Triglyceride molecules consist of 3 fatty acids (blue) linked to a glycerin molecule -Triacylglycerols function as energy reservoirs in animals and are therefore their most abundant class of lipids even though they are not components of cellular membranes. -nonpolar, water-insoluble substances are fatty acid triesters of glycerol The fats and oils that occur in plants and animals consist largely of mixtures of? energy reserves/store metabolic energy -This is because triacylglycerols are less oxidized than carbohydrates or proteins and hence yield significantly more energy per unit mass on complete oxidation. -Are non polar -energy rich Their main role in cells is to store excess fatty acids, and they are mostly found within lipid droplets. -Energy is mostly stored in fat molecules in Triacylglycerols. T