Chapter 8 Lipids

Lipids

Lipids

• hydrophobic/amphipathic

• fats/oils/vitamins/hormones/non-protein membrane components

Major purposes of lipids

• energy storage

• cell membrane development

• serving as a component of hormones/vitamins

Major classes of lipids

• fatty acids

• triacylglycerols

• glycerophospholipids

• sphingolipids

• waxes

• isoprene-based lipids

Fatty Acids

• long carbon chain + carboxylic acid

• commonly found in esterified form with glycerol

• saturated or unsaturated

Unsaturated

• contains double bonds

• classified as omega 3, omega 6, or omega 9

Saturated fatty acids (let me pack saturated acid)

• lauric acid 12C

• myristic acid 14C

• palmitic acid 16C

• stearic acid 18C

• arachidic acid 20C

Lauric Acid

• saturated

• 12 carbons

Myristic Acid

• saturated

• 14 carbons

Palmitic Acid

• saturated

• 16 carbons

Stearic Acid

• saturated

• 18 carbons

Arachidic Acid

• saturated

• 20 carbons

Unsaturated fatty acids (pocket only lean alphas gammas and arachnids)

• palmitoleic acid 16:1 omega 7

• oleic acid 18:1 omega 9

• linoleic acid 18:2 omega 6

• alpha-linolenic acid 18:3 omega 3

• gamma-linolenic acid 18:3 omega 6

• arachidonic acid 20:4 omega 6

Palmitoleic Acid

• unsaturated

• 16:1

• omega 7

Oleic Acid

• Unsaturated

• 18:1

• omega 9

Linoleic Acid

• unsaturated

• 18:2

• omega 6

Alpha-Linolenic Acid

• unsaturated

• 18:3

• omega 3

Gamma-Linolenic Acid

• Unsaturated

• 18:3

• omega 6

Arachidonic Acid

• unsaturated

• 20:4

• omega 6

what configuration are most unsaturated fatty acids in? how does it affect the chain?

• cis configuration

• causes bend/kink

how does the saturation level affect lipid fluidity?

lower levels of saturation result in higher lipid fluidity and lower melting points

what essential fatty acids are not synthesized by mammals?!

• linoleic acid (obtained from diets)

• alpha-linolenic acid

why is arachidonic acid important?!

• not in plants

• synthesized by animals from linoleic acid

• can create essential molecules and precursors for hormones

what class of compounds can fatty acid be a precursor for?

essential fatty acids can serve as a precursor for synthesis of eicosanoids ex. prostaglandins that exert hormone-like effects on processes

How are trans fatty acids formed?

Trans fatty acids are formed by some bacteria via double bond migration and isomerization.

ex. found in butter, milk, animal meat

How are processed fats formed?

Formed via partial hydrogenation of polyunsaturated oils

Consequences of diets high in trans/saturated fats

• increased risk for heart disease/strokes

• high low-density lipoprotein (LDL) cholesterol

• low HDL cholesterol

Triacylglycerols (triglyceride)

• glycerol esterified with three fatty acids

• same fatty acids = simple TAG

• different fatty acids = mixed TAG

why are triacylglycerols a major energy source?

• rich in highly reduced carbons used in oxidative reactions

• hydrophobic nature allows them to aggregate in highly anhydrous forms (high energy density)

Glycerophospholipids

• glycerol motif

• phosphate group esterified at C3

• one of the largest groups of lipid

• essential cell membrane component

Phosphatidic acid

• parent compound

• important intermediate in the biosynthesis of the more common glycerophospholipid

• -OH group connected to P

Ether glycerophospholipids

• ether linkage at C1 instead of hydroxyl

• ex. platelet activating factor (PAF) a signal molecule

Sphingolipids

• an 18 carbon amino alcohol (sphingosine) backbone instead of glycerol

• a fatty acid is joined via amide linkage

• ex. sphingomyelins

Glycosphingolipids

• ceramides with one or more sugars in a glycosidic linkage at the 1-hydroxyl group

Waxes

• esters of long-chain alcohols with long-chain fatty acids

• insoluble

• animal skin and fur, plant leaves, bird feathers are wax-coated

• ex. Lanolin is a wool wax used in cosmetics

Terpenes

• class of lipids formed from combinations of two or more isoprene molecules

• head to tail linkage

• tail to tail linkage

• can be found in lipid anchoring proteins and squalene

Squalene

an important intermediate in cholesterol synthesis

Monoterpenes

• consist of two isoprene units

• occur in all higher plants i.e. lemons, roses, etc

• ex. limonene, citronellal

Sesquiterpenes

• consist of three isoprenes

• ex. bisabolene

Diterpenes

• consist of four isoprene units

• ex. phytol

Gonane

a common motif for steroids

Cholesterol

• principle component of animal plasma membranes

• weakly polar due to hydroxyl group on C3

• amphipathic polar nature allows it to enter membranes and disrupt packaging

How does cholesterol affect the permeability of the plasma membrane?

• hydroxyl group interacts with polar headgroups of the membrane

• bulky steroid and alkyl chain is embedded in the membrane

• reduced permeability to protons and sodium ions

• provides stability to cell membrane

Describe the relationship between hormones and receptors using affinity and concentration

• Hormones travel through bloodstream to enter cells and bind to highly specific receptor

• Hormones have high affinity for their receptors = low concentration of hormone is sufficient

What does Km represent?

• michaelis menten constant

• [S] when Vmax is ½

What does Kd represent?

• enzyme affinity for a substrate/ligand

• Low Kd = greater affinity

• High Kd = weaker affinity

What does Kcat represent?

• Kcat = K2

• the number of times the enzyme converts substrate to product per unit of time

What is considered low Kd?

• low Kd = greater affinity = low [S] required

• 100 microMolar or less

What are some hormone families derived from cholesterol in animals?

• Androgens

• Progestins

• Glucocorticoids

What are the bile acids?

• cholic acid and deoxycholic acid

• significant role in repackaging fatty acids

• detergent molecules assisting in breakdown of dietary lipids for oxidation

What is the active form of vitamin D?

1,25-dihydroxycholecalciferol

Step 1: vitamin D synthesis

substrate: cholesterol precursor

→→→

product: 7-hydroxycholecalciferol

Step 2: vitamin D synthesis

substrate: 7-hydroxycholecalciferol

sun → skin

product: cholecalciferol

Step 3: vitamin D synthesis

substrate: cholecalciferol

25-hydroxylase → liver

product: 25-hydroxycholecalciferol

Step 4: vitamin D synthesis

substrate: 25-hydroxycholecalciferol

1-a-hydroxylase → kidney

product: 1,25-dihydroxycholecalciferol

What are the physiological effects of vitamin D?

• hormone involved in mineral metabolism and bone growth

• facilitate intestinal absorption of calcium/phosphate/magnesium

What are some disease states of vitamin D?

• Rickets - deficiency in babies that results in bone deformities ex. bowed legs

• Osteomalacia - deficiency in adults that results in soft/weak bones