lipids

what are lipids

they are a heterogeneous class of organic compounds that share two common properties:

insolubility in aqueous or water based solutions

solubility in organic or non-polar solvent

what are the functions of lipids

membrane structure, energy storage, signaling molecules

what are fatty acids

they are amphipathic molecules with carboxylic acid group binding to hydrocarbon chains containing between 3-35 carbons

what are characteristics of fatty acids

almost all of them have an even number of carbons

most natural ones are unbranched

the pKa of COOH group is <5 and at pH 7, they have an ionized carboxylate

what is the difference between saturated and unsaturated

saturate=no double bonds between carbon in the chain vs unsaturated=one or more double bonds between carbons in the alkyl chain

what is the nomenclature for fatty acids

the systemic name is cis-9-octadeceoic acid and the common name is oleic acid and the numbering of carbon atoms start at the COOH group (#1)

what is the process of delta numbering of a carbon skeleton

it starts at the first carbons of the alkene which is the carboxyl carbon

what is the process of omega numbering of a carbon skeleton

it starts at the terminal methyl of the alkene

what are essential lipids

they are lipids that humans need but can’t synthesize so they are essential nutrients in the diet

what are examples of essential lipids

linoleic acid (omega 6) 18:2 delta9, 12

linolenic acid (omega 3) 18:3 delta 9, 12, 15

what happens to the solubility of fatty acids as the chain length increases

it decreases as the chain length increases

when does the melting point of fatty acids decrease

it decreases as the chain length increases and as the number of double bonds increases

what type of fatty acids have a lower melting point

unsaturated cis fatty acids have a lower one

how do trans fatty acids form

they form by partial hydrogenation of unsaturated fatty acids and cis-double bond isomerization to trans-double bonds

what does a trans double bond allow for

it allows for a given fatty acid to adopt an extended conformation

what are characteristics of trans fatty acids

they can pack more regularly and show higher melting point than cis forms

why are high saturated and trans fat bad for health

saturated fatty acids increase blood glucose levels by providing proper packing domains for cholesterol and trans-fats do the same, together with increased rigidity around the double bonds

how does high cholesterol create a higher incidence of heart disease

it reduced membrane fluidity, flexibly and protein functions

what are storage lipids

they are non-polar lipids and can be triglycerides or waxes

what do acyglycerols result from

they result from a condensation reaction between one glycerol sugar with one, two, or three fatty acids

what are glycerol and fatty acids linked by

they are linked by ester linkage

what is the chiral center in a triglyceride complex

C2 would be the chiral center

what form are most fatty acids in a biological system found as

they are found in the form of triacylglycerols, solid ones are called fats and lipid ones are called oils

what are characteristics of triglycerides

they are the primary storage form of lipids in animals and plants, they are less soluble in water than fatty acids due to the esterification of the carboxylate group and they are less dense than water

what are the advantages of fats over polysaccharides

fatty acids carry more energy per carbon because they are more reduced and fatty acids carry less water per gram because they are non polar

what leads to the hydrolysis of the ester bond between glycerol and fatty acids

the treatments of triacylglycerols with a strong base

what are triglycerides

they are storage lipids formed by condensation reactions between glycerol alcohol groups and carboxylic acids of saturated or unsaturated fatty acids through an ester bond or linkage

what are the physical properties of triglycerides governed by

they are governed by the length of the fatty acid chains and their degree of saturation

what does triglyceride hydrolysis with lipase result in

it results in fatty acids and glycerol for energy production

what does triglyceride hydrolysis with strong acids or bases result in

it results in fatty acid salts and glycerol used for commercial production of soaps

what are waxes

they are esters of long-chain saturated and unsaturated fatty acids with long chain alcohols, they are insoluble and have high melting points higher than triglycerides and unlike triacylglycerides they don’t contain glycerol

what are the functions of waxes

storage of metabolic fuel in plankton

waterproofing of feathers in birds

protection from evaporation in tropical plants and ivy

used by people in lotions, ointment and polishes

what are the polar lipids

they are structural lipids like glycerophospholipids and sphingolipids

where does diversification of structural lipid in membranes come from

modifying a different backbone

changing the fatty acid

modifying the head groups

what are structural lipids in membranes made up of

they contain polar head groups and non polar tails and are usually attached to fatty acids

what are characteristics of structural lipids in membranes

the properties of the head groups determine the surface properties of membranes

different organisms have different membrane lipid head group compositions

different tissues have different membrane lipid head group compositions

what are glycerophospholipids

they are the primary constituents of cell membranes and are two fatty acids that form ester linkages with the first and second hydroxyl groups of l-glycerol-3-phosphate. the phosphate group is negatively charged at pH 7

what is phosphatidylcholine

it is the major component of most eukaryotic cell membranes and many prokaryotes cannot synthesize it

what are phospholipases A-D

they are what degrade phospholipids as cells continuously degrade and replace their membranes

how are fatty acids and alcohol head groups linked to glycerol or phospatidic acid in glycerophospholipids

they are linked by an ester or phosphoester bond respectively

what does the differential distribution of glycerophospholipids cause

it gives cell membranes their overall positive or negative surface charges

what is the backbone of sphingolipid

it is a long-chain amino alcohol called sphingosine

what makes up a sphingolipid

a fatty acid is going to sphingosine via and amide linkage rather than an ester one. a polar head group is connecting to sphingosine by a glycosidic or phosphoester linkage

what is ceramide

it is the parent compound from which sphingolipids are derived, it is similar to diacylglycerol

what is spingomyeline

it is the addition of a phosphocholine group to sphingosine

what is cerebroside

it is the addition of mono-sugar group to sphingosine and is present in the sheaths of nerve fibers

what is globoside

it is the addition of di, try, or tetrasaccharide to sphingosine

what is ganglioside

it is the addition of a combination of sugars or oligosaccharides to spingosine

where are the sugar-containing glycospingolipids commonly found

they are commonly found in the outer face of plasma membrane and consequently detectable by the immune system

what is sphingomyelin

it is a ceramide (sphingosine and amide-linked fatty acid) and phosphocholine attached to the alcohol

where is there a lot of sphingomyelin

there is a lot of it in myeline sheath that surrounds some nerve cells in animals

what is sphingomyelin structurally similar to

it is similar to phosphatidylcholine

what are blood groups determined by

they are determined in part by the type of sugars located on the head groups in glycosphingolipids

what is the structure of sugar of the head groups of glycosphingolipids determined by

it is determined by the expression of specific glycosyltransferases

who will have the O antigen

individuals with no active glycosyltransferase will have it

who will be in the A blood group

individuals with a glycosyltransferase that transfers an N-acetylgalactosamine will be in it

who will be in the B blood group

individuals with a glycosyltransferase that transfers a galactose group will be in it

what do sphingolipids lack

they lack the glycerol backbone

what do sphingolipids contain

they have one fatty acid at C2 of the sphingosine chain attached through an amide bond and some contain a phosphoric acid at C1 of the sphingosine chain while others contain sugar groups (like cerebrosides and gangliosides)

why do sphingolipids tend to target

they tend to target specific tissue membranes and are generally localized to the outer layer of the cell membrane

what is a characteristic of spingolipids

they all contain ceramide joined to a polar group

what are the products of phospholipase D degradation of phosphatidylethanolamine

phosphatidate and ethanol amine

what are characteristics of biologically active lipids

they don’t have fatty acids or glycerol backbones but some can be generated from fatty acids

occur is much smaller amounts if cells and tissues

play major physiologic roles by recruiting the activities of proteins and receptors

what are the major classes of biologically active lipids

steroids and eicosanoids

what are steroids

they are generated from two carbon acids and through modification of other sterols. they are important metabolically for digestion and as hormones

how are eicosanoids generated

they are generated through modification of fatty acids

what is sterol made up of

steroid nucleus: 4 fused rings, almost planar

hydroxyl group (polar head) in A-ring

various non polar side chains

what do cholesterol and sterols do

they are present in the membranes of most eukaryotic cells

modulate fluidity and permeabilit

thicken the plasma membrane

no sterols in most bacteria

how do mammals obtain cholesterol

they obtain is from food or synthesize it de novo in the liver

how is cholesterol transported

bound to proteins, it is transported to tissues via blood vessels and in low density lipoproteins it tends to deposit and clog arteries

what are many hormones derivatives of

they are derivatives of sterol

what are characteristics of steroids

they are oxidized derivatives of sterols

they have sterol nucleus but lack alkyl chain found in cholestero

more polar than cholesterol

synthesized from cholesterol in gonads and adrenal glands

carried through body in bloodstream, usually attached to carrier proteins

many steroid hormones are male/female sex hormones

what yields eicosanoids

the enzymatic oxidation of arachidonic acid yields it

what are the types of eicosanoids

prostaglandins (inflammation and fever)

thromboxane (formation of blood clots)

leukotrienes (smooth muscle contraction in lungs)