Biochemistry-Chapter 8: Lipids

Classes of lipids

fatty acids, triacylglycerols, glycerophospholipids, sphingolipids, waxes, isoprene derived lipids (includes steroids)

fatty acids

~have long hydrophobic tails with carboxylic acid (ionized under physiological pH)

~usually 12-24 carbons in length

~saturated hydrophobic tails (no pi bonds)

~unsaturated have at least one pi bond

~pi bonds are almost always cis (not trans) and it adds a kink

~saturated pack closely together

~unsaturated cannot pack as close

triacylglycerols

~most fatty acids in plants and animals exist as this

~major source of energy storage in animals (release more energy than sugars and proteins when metabolized)

mixed triacylglycerols

~2 or 3 different fatty acids

~found in adipose tissue

~mono and diacyl glycerol are less common

why do triacylglycerols yield more energy upon metabolism

~fatty acids are at a lower oxidation level than carbohydrates and proteins

~hydrophobic nature of triacyclglycerols allow them to be stored in Anhydrous form (without H2O)

glycerophospholipids

~1,2 diacylglycerol + C3OH is esterified with phosphate

~largest most important group of natural lipids

~essentially all cell membranes and other cellular components are composed in part of this class of lipids

~ Phosphatic acid undergoes acylation with head groups

~unsaturated fatty acids will be at C2

~head groups: choline, phosphatidyl serine

ether glycerophospholipids

~have an ether group at C1

~platelet activating factor

~plasmalogens

Platelet Activating Factor (PAF)

~initiates inflammatory responses

~cell signaling molecule

~has acetate at C2

~acetate allows for solubility (soluble messenger molecule)

plasmalogens

~ether group has a C1 cis double bond

~found in neurons and immune system

~levels are elevated in cancer cells also has a protective role

~found in membranes (where cholesterol is in high concentration)

~involved in cell signaling and recognition

~form lipid rafts with enolesterol

glycosphingolipids

~have one or more sugars in beta orientation at C1 alcohol

~cerebroside (has a single glucose or galactose)

~ganglioside complex derivative of the cerebroside

waxes

~esters formed from long chain fatty acids and long chain alcohol

~insoluble in water

~found in animal skin, feathers, coatings on leaves (repel water)

Terpenes

straight chain or cyclic structure formed from isoprene units

steroids

~terpene based lipids with a unique ring structure

~3 cyclohexanes + 1 cyclopentane fused together

~C3 is oxygenated

~methyl group usually at C10 and C13

~alkyl group (chain) of approximately 10C at C17

~can have other functional groups

hormones derived form cholesterol

progestins, glucocorticoids, mineral corticoids, androgens, estrogens

progestins

female reproduction (ex: progesterone)

glucocorticoids

regulate metabolism; inflammation suppression (ex: cortisol)

mineral corticoids

regulate salt and water balance (ex: aldosterone)

androgens

male sex hormone (ex: testosterone)

estrogens

female sex hormone (ex: estradiol or esterone)