CHM 365 Chapter 7

What are the characteristics of lipids?

soluble in NP solvents

amphipathic

aggregate (driven by HE)

Function of lipids

structural, long term energy storage, signaling

What are the 5 major classes of lipids?

fatty acids

triacylglycerols

glycerophospholipids

sphingolipids (sphingomyelines, cerebrosides, gangliosides)

steroids

Fatty Acids

Carboxylic acids with long chain hydrocarbon

can be saturated (fats) or unsaturated (oils) (double bonds → cant pack as tightly and are easier to displace)

Melting point increases as the hydrocarbon chain gets longer due to increased LD forces

Triacylglycerols

fatty acid triesters of glycerol

NP/water insoluble and serve as energy reservoirs in animals

Form globules inside cells

Adipocytes

fat globule of triacylglycerols; synthesize TAGs

long term energy storage molecules (have higher energy density than carbs)

Glycerophospholipids

main lipid in biological membranes consists of glycerol-3-phosphate esterified with fatty acids at C1 and C2 with a phosphoryl group linked to a polar group

amphilic molecules

Plasmalogen

Glycerophospholipid with a/b unsaturated ether linkage at C1

Antioxidant- reacts with reactive oxygen/notrofen species preventing free-radical damage

Phospholipases

hydrolyze Glycerophospholipids (breaks off fatty acid tail)

Ceramides

1 sugar unit with a sphingosine backbone

tends to be stiffer than PG

contains an N-acyl fatty acid derivative

Sphingomyelin

has phosphocholine or phosphoethanolamine head group

makes up the myelin sheath insulating nerve cell axons

Gangliosides

oligosaccharides

Cholesterol

steroid that has polar OH group giving it weak amphiphilic character

biodirectional stabilizer of cell membrane

Vit D

Steroid that regulated Ca2+ metabolism (promotes absorption)

undergoes non-enzymatic ring breaking at the B ring by UV

can undergo two hydroxylations

deficiency-rickets

Ubiquinone

Isoprenoid (co-enzyme Q)

a part of the mitochondrial ETC

reversibly reduced and oxidized in the mitochondrial membrane

Vit A

isoprenoid (retinol)

precursor is B carotene

deficiency-blindness

Vitamin K

isoprenoid

fat soluble

essential for carboxylating Glu residues in clotting proteins

deficiency-excessive bleeding

Vit E

isoprenoid

Antioxidant and will react with reactive oxygen and nitrogen species to prevent oxidative damage to membrane proteins and lipids

Micelle

single-tailed lipids undergo HE to form spherical micelles

Lipid Bilayer

Formed by glycerophospholipids and sphingolipids to form two layers with hydrophobic tail interior and hydrophilic head group exterior

Kinks in Lipid bilayer

makes the membrane more fluid, helps to mitigate lower temperatures

Transverse Diffusion

flip-flop acriss the membrane

not spontaneous:

-flippase (cytosolic side); floppase (extracellular side); scramblase (both directions)

Lateral Diffusion

Within a leaflet

occurs rapidly (spontaneously)

Gelling of Membrane

occurs below transition temperature

What are the three types of membrane proteins?

Integral (intrinsic)

Lipid-linked

Peripheral (extrinsic)

Integral (intrinsic) proteins

tightly bound to membrane; amphipathic, mainly transmembrane proteins that cross membrane (a helicies and B sheets)

Lipid Linked

Membrane protein covalently attached to a lipid

Peripheral (extrinsic) proteins

not tightly bound to membrane and are easier to move

interactions are mostly due to electrostatics (charge-charge) and H-bonding

Human Epidermal Growth Factor Receptor

intrinsic protein

Bacteriorhodopsin

seven a-helical rods that span the lipid bilyer in directions almost perpendicular to the bilayer plane

OmpF

Integral Protein

Porin→ B Barrel Trimer that has a.a within to filter molecules

Prenylated Protein

lipid linked

C term tetra peptide: Cys-x-x-Y

(X is aliphatic A.A)

Cytochrome C

peripheral membrane protein

What are the three main factors that impact membrane fluidity?

1. phosphoglyceride composition: short f.a.=more fluid and higher unsaturation percentage=more fluid due to kinks

2. cholesterol - bidirectional regulator of membrane fluidity

3. temperature: higher temperature=more fluid; lower temperature=gelled membrane