ABI 103 UC Davis

Lipids and Biological Membranes *Lipid Classification*

Lipids 3 biological Functions

1) essetial to membranes (lipid bilayer)

2) energy storage (hydrocarbon chains)

3) cellular signaling

Are lipids polymeric?

No, but can form aggregates

Lipid Physical properties determined by:

1) Length (# of carbons)

2) Saturation (double bonds)

Lipids are soluble in what solvents?

organic

how are lipids seperated?

by extraction into organic solvents, easily

Fatty Acids

Carboxylic acids with long chain

Common C length of Fatty acids

C16 and C 18 in higher plants/animals

C14-C20 all possible others uncommon

Do Fatty acids have an even or odd amount of C’s? Why?

even, because they are put together in C2 units

Percent of Fatty acids that are unsaturated?

more than 50%

• many are polyunsaturated (multiple double bonds)

Saturated

No double bonds

Unsaturated

contains double bonds

Saturated Fatty Acids Characteristics

• highly felxible moleciles

  • free rotation of c-c bonds allows for many conformations

how is melting point affected by saturation (saturated)?

MP of saturated fatty acids increases with molecular mass (# of carbons)

Unsaturated Fatty Acids Characteristics

double bonds have cis configuration

pack together less effeciently

How is MP affected by saturation (unsaturated)?

MP decreases with number of double bonds

Triacylglycerols (TG’s)

nonpolar

water-insoluable

glcycerol+3 esterified fatty acids

Fucntions of Triacylglycerols

• energy reservoirs in animals

• MOST abundant class of lipids

• differ by placement and identity of fatty acid residues

common characteristics in MOST TG’s

• 2 or 3 different Fatty acid residues

  • named by placment on glycerol moieties

Fats

solid at room temp

highly effecient at storing metabolic energy

Oils

liquid at room temp

what leads to the lower melting points of oils?

plant oils richer in unsaturated residues than animal fats

Adipocytes

specialized for TGs synthesis and storage

Adipocytes composition

• may be all fat globules

Adipose Tissue

• abundant in SQ layer and in abdominal cavity

Adipocytes purpose

• fat of humans allows to survive starvation for 2-3 months

  • SQ fat layer provides thermal insulation

Thermal Insulation Importance

• for mammals living in cold water

Phosphoglycerides/ Glycerophospholipids (PGs)

major lipid components of biological membranes

• C1 and C2 positions are esterified w/ FAs

  • phophoryl group linked to group (usually polar)

PG Characteristics

amphiphilic molecules with nonpolar tails and polar heads

Simplest PG is ?

phosphoatidic acids

• present in small amounts in membranes

Common PG Classes

head groups often derived from polar alcohols

C1 usually has a saturated C16 or C18

C2 usually an unsaturated C16-C20

named by identities of FA residues

Phospholipases

Enzymes that cleave off lipids and different FA residues through hydrolytic reactions of phosphoglycerides

Lysophospholipases

powerful detergents that disrupt cell membranes (cell lysis)

• bee and snake venoms rich in these

Signal Molecules

products of membrane hydrolysis sometimes serve as intra and extracellular signal molecules when not destined for further degredation

Lysophosphatidic acid (LPA)

produced by hydrolysis of membrane lipids in blood platlets and injured cells

• stimulates cell growth as part of the wound repair process

1,2-Diacylglycerol

derived from membrane lipids by the action of phospholipace C

• intracellular signmal molecule that activated a protein kinase

protein kinase

stimulate/ enhances signals in cell

Plasmalogens

phosphoglyceride

• C1 substituent of the glycerol moiety linked via an alpha/beta-unsaturated ether linage in the cis configuration

Common feature of plasmalogens

• all have glycerol

Sphingolipids

derivatives of the C18 amino alcohol sphingosine (double bond with a trans configuration)

Ceramide

• N-acyl fatty acid derivatives of sphingosine

  • important for brain function and nerve transmission

parent compound of the more abundant sphingolipids

Abundant sphingolipids

1) sphingomyelins

2)cerebrosides

3)gangliosides

Sphingomyelins

MOST common sphingolipids

• ceramides baring phosphocholine/phosphoethanolamine head group

  • 10-20% of mol weight of plama membrane lipids

Phosphocholine

phosphoethanolamine

Sphingomyelins and phosphatidylcholine

differ chemically but conformations and charge distributions are similar

Sphingomyelins (myelin sheath)

surrounds and electrically insulates many nerve exon cells

• prevents nerve to leave the cell and signal

Cerebrosides

ceramides with head groups that consist of a SINGLE sugar residue

galacto and gluco are the most prevalent

lack phosphate groups (non ionic)

gangliosides

most complex glycosphingolipids

ceremides attached oligosaccharides that include at least ONE SIALIC ACID residue

Ganglioside purpose

primarily components of cell-surface membranes

(6%) of brain lipids

complex carb head group that acts as specific receptors for pituitary glycoprotein hormones

receptors for bacterial protein toxins

Steroids

eukaryotic origin

deriviatives of cyclopentanoperhydrophenanthrene

cyclopentanoperhydrophenanthrene

compound with four fused nonplanar rings

attachments can include open rings and hydrocarbon tails

Cholesterol

• most abundant steroid in animals

• major component of animal plasma membranes

• classified as a sterol because of its C3 OH group

Cholesterol purposes

• 30-40% mol weight of plasma membrane lipids

• polar OH group causes weak amphiphilic character

• fused ring system provides it greater rigidity

• can be esterifies to long chain FAs to form cholesterol ethers

Cholesterol in Plants

little (synthesize other sterols )

Cholesterol in yeast and fungi

synthesize sterols

• differ from cholesterol in their aliphatic side chains and number of double bonds

Cholesterol in prokaryotes

• little if any its sterol

Cholesterol role in Steroid Hormones in mammals

its a metabolic precursor of steroid hormones

Steroid Hormones

• regulate a variety of physiological functions

• classified according to the physiological responses they evoke

Steroid Hormone Classifications

1) glucocorticoids

2)mineralocorticoids

3)androgens and estrogens

Glucocorticoids

C21 compound (ex. Cortisol)

• affect carb, protein, and lipid metabolism

• influence variety of vital functions

Mineralocorticoids

regulate the excretion of salt and water by the kidneys

Androgens and Estrogens

affect sexual development and function

• testosterone Prototypic androgen

  • B-estradiol is an estrogen

Steroid Hormones transport through blood

water insoluble

bind to proteins

for blood transport to target tissues

• we generate them, local production, need to be transported

Vitamin D

sterol derivatives

disrupted steroid B ring between C9 and C10

Vitamin D2

Formed non-enzymatically

• animal skin

• photolytic actin of UV light on plant sterol

• precursor to vitamin D

Vitamin D role in Calcium Metabolism

Vitamins D 2 and 3 are inactive

Active forms are made through their enzymatic hydroylation, addition of OH

carried out by the liver at C25 and kidney at C1 to make (1alpha,25dihydroxycholecalciferol)

Active Vitamin D role in Calcium metabolism

promotes intestinal absorbtion of dietary calcium

• increased serum and deposition of calcium in bones and teeth

• water insoluble

• accumulate in fatty tissue

Excessive intake of Calcium

• results in Vitamin D intoxication

Increase in serum Calcium

leads to calcification of soft tissues

kidney stones

Skin Pigmentation (Vitamin D)

• increases with proximity to equator

  • filters excessive solar radiation to prevent vitamin D intoxication

Isoprenoids (other lipids)

soluble in the lipid bilayer

not structural components of the membrane

build from C5 units with same carbon skeleton as ISOPRENE

Coenzyme Q (isoprenoids)

reversible reduces and oxidized in the mitochondrial membrane

• mammalian ubiquinone consists of 10 ISOPRENE unts

Plants (isoprenoids)

rich in isoprenoid compounds

• act as pigments, molecular signals (hormones and pheremones), and defensive agents

  • 25k+ (mostly plant, fungal, bacterial origin)

Vertebrates (isoprenoids)

• some compounds fat soluble

  • vitamins are requires in small amounts but cannot be made must be consumed

Plant Isoprenoids Vitamin A

derived mainly from plant products (Beta-carotene)

Vitamin A (Retinol)

oxidized to its corresponding aldehyde (retinal)

Retinal

functions as the eye’s photoreceptor at low light intensities

Vitamin A deficiency

severe deficiency of vitamin A can lead to blindness

Retinoic Acid

hormone-like properties:

• stimulates tissue repair

• used to treat severe acne and skin ulcers

• cosmetically to eliminate wrinkles

Vitamin K (plant and bacterial isoprenoids)

lipid synthesized by plants and bacteria

Vitamin K synthesized in plants

phylloquinone

Vitamin K synthesized in bacteria

menaquinone

Vitamin K purpose

• half of daily requirements supplies by intestinal bacteria

  • participates in carboxylation of glutamic acis residues in some of the proteins involved in blood clotting

Vitamin K deficiency

• prevents carboxylation of Glu residues

• inactive clotting proteins

• excessive bleeding

Vitamin E

group of compounds with most abundant being alpha-tocopherol

• highly HYDROPHOBIC molecule

• incorporated into cell membranes

Vitamin E Functions

• functions as antioxidant preventing oxidative damage to membrane proteins and lipids

Prostaglandins (other lipids)

known as eicosanoids

ALL are C20 compounds

Eicosanoids

act at very low concentrations

Eicosanoids involved in:

production of pain and fever

regulation of blood pressure and blood coagulation

regulation of reproduction

Where do Ecoisanoids act?

act LOCALLY, close to cells that produce them

decompose within seconds/minutes

limits their effects on nearby tissues

Arachidonic Acid

MOST important eicosanoid precursor in humans

• polyunsaturated FA with FOUR double bonds

  • stored in cell membranes as C2 ester of phosphatidylinositol/other phospholipids

Arachdonic Acid Function

FA residue is released by the action of phospholipase A2

specific products of its metabolism are tissue dependent

Aspirin inhibits formation of prostaglandin H2

Arachdonic Acid —> Aspirin Inhibits —> no more pain/fever